Staff directory Josep Nogués Sanmiquel

Josep Nogués Sanmiquel

ICREA Research Professor and Group Leader
josep.nogues(ELIMINAR)@icn2.cat
Magnetic Nanostructures

ORCID: 0000-0003-4616-1371
Researcher ID: D-7791-2012
Google Scholar: Visit

Publications

2024

Elucidating the Lithiation Process in Fe3-δO4 Nanoparticles by Correlating Magnetic and Structural Properties
Ulusoy, Seda; Feygenson, Mikhail; Thersleff, Thomas; Uusimaeki, Toni; Valvo, Mario; Roca, Alejandro G; Nogues, Josep; Svedlindh, Peter; Salazar-Alvarez, German Acs Applied Materials & Interfaces; 16 (12): 14799 - 14808. 2024. 10.1021/acsami.3c18334.
Fe/Au galvanic nanocells to generate self-sustained Fenton reactions without additives at neutral pH
Shahnazarova, Gubakhanim; Al Bast, Nour Al Hoda; Ramirez, Jessica C; Nogues, Josep; Esteve, Jaume; Fraxedas, Jordi; Serra, Albert; Esplandiu, Maria J; Sepulveda, Borja Materials Horizons; 11 (9): 2206 - 2216. 2024. 10.1039/d3mh01935g.
The efficient magneto-mechanical actuation of cancer cells using a very low concentration of non-interacting ferrimagnetic hexaferrite nanoplatelets
Gorsak, T; Jovicic, EJ; Tratnjek, L; Krizaj, I; Sepulveda, B; Nogues, J; Kreft, ME; Petan, T; Kralj, S; Makovec, D Journal Of Colloid And Interface Science; 657: 778 - 787. 2024. 10.1016/j.jcis.2023.12.019.

2023

Elucidating Individual Magnetic Contributions in Bi-Magnetic Fe3O4/Mn3O4 Core/Shell Nanoparticles by Polarized Powder Neutron Diffraction
Golosovsky, IV; Kibalin, IA; Gukasov, A; Roca, AG; López-Ortega, A; Estrader, M; Vasilakaki, M; Trohidou, KN; Hansen, TC; Puente-Orench, I; Lelièvre-Berna, E; Nogués, J Small Methods; 7 (10): e2201725. 2023. 10.1002/smtd.202201725. IF: 12.400
Enhanced Proliferation and Differentiation of Human Osteoblasts by Remotely Controlled Magnetic-Field-Induced Electric Stimulation Using Flexible Substrates
Careta, O; Nicolenco, A; Perdikos, F; Blanquer, A; Ibañez, E; Pellicer, E; Stefani, C; Sepúlveda, B; Nogués, J; Sort, J; Nogués, C Acs Applied Materials & Interfaces; 15 (50): 58054 - 58066. 2023. 10.1021/acsami.3c09428. IF: 9.500
Iron oxide nanoparticles (Fe3O4, γ-Fe2O3 and FeO) as photothermal heat mediators in the first, second and third biological windows
Roca, AG; Lopez-Barbera, JF; Lafuente, A; Özel, F; Fantechi, E; Muro-Cruces, J; Hémadi, M; Sepulveda, B; Nogues, J Physics Reports; 1043: 1 - 35. 2023. 10.1016/j.physrep.2023.10.003. IF: 29.900
Modular Drug-Loaded Nanocapsules with Metal Dome Layers as a Platform for Obtaining Synergistic Therapeutic Biological Activities
Fluksman, A; Lafuente, A; Braunstein, R; Steinberg, E; Friedman, N; Yekhin, Z; Roca, AG; Nogues, J; Hazan, R; Sepulveda, B; Benny, O Acs Applied Materials & Interfaces; 15 (43): 50330 - 50343. 2023. 10.1021/acsami.3c07188. IF: 9.500
Soft Optomechanical Systems for Sensing, Modulation, and Actuation
Pujol-Vila, F; Guell-Grau, P; Nogues, J; Alvarez, M; Sepulveda, B Advanced Functional Materials; 33 (14) 2023. 10.1002/adfm.202213109. IF: 19.000

2022

Crossover From Individual to Collective Magnetism in Dense Nanoparticle Systems: Local Anisotropy Versus Dipolar Interactions
Sánchez E.H., Vasilakaki M., Lee S.S., Normile P.S., Andersson M.S., Mathieu R., López-Ortega A., Pichon B.P., Peddis D., Binns C., Nordblad P., Trohidou K., Nogués J., De Toro J.A. Small; 18 (28, 2106762) 2022. 10.1002/smll.202106762.

Dense systems of magnetic nanoparticles may exhibit dipolar collective behavior. However, two fundamental questions remain unsolved: i) whether the transition temperature may be affected by the particle anisotropy or it is essentially determined by the intensity of the interparticle dipolar interactions, and ii) what is the minimum ratio of dipole–dipole interaction (Edd) to nanoparticle anisotropy (KefV, anisotropy⋅volume) energies necessary to crossover from individual to collective behavior. A series of particle assemblies with similarly intense dipolar interactions but widely varying anisotropy is studied. The Kef is tuned through different degrees of cobalt-doping in maghemite nanoparticles, resulting in a variation of nearly an order of magnitude. All the bare particle compacts display collective behavior, except the one made with the highest anisotropy particles, which presents “marginal” features. Thus, a threshold of KefV/Edd ≈ 130 to suppress collective behavior is derived, in good agreement with Monte Carlo simulations. This translates into a crossover value of ≈1.7 for the easily accessible parameter TMAX(interacting)/TMAX(non-interacting) (ratio of the peak temperatures of the zero-field-cooled magnetization curves of interacting and dilute particle systems), which is successfully tested against the literature to predict the individual-like/collective behavior of any given interacting particle assembly comprising relatively uniform particles. © 2022 The Authors. Small published by Wiley-VCH GmbH.

View abstract
Elastic Plasmonic-Enhanced Fabry–Pérot Cavities with Ultrasensitive Stretching Tunability
Güell-Grau P., Pi F., Villa R., Eskilson O., Aili D., Nogués J., Sepúlveda B., Alvarez M. Advanced Materials; 34 (7, 2106731) 2022. 10.1002/adma.202106731. IF: 30.849

The emerging stretchable photonics field faces challenges, like the robust integration of optical elements into elastic matrices or the generation of large optomechanical effects. Here, the first stretchable plasmonic-enhanced and wrinkled Fabry–Pérot (FP) cavities are demonstrated, which are composed of self-embedded arrays of Au nanostructures at controlled depths into elastomer films. The novel self-embedding process is triggered by the Au nanostructures’ catalytic activity, which locally increases the polymer curing rate, thereby inducing a mechanical stress that simultaneously pulls the Au nanostructures into the polymer and forms a wrinkled skin layer. This geometry yields unprecedented optomechanical effects produced by the coupling of the broad plasmonic modes of the Au nanostructures and the FP modes, which are modulated by the wrinkled optical cavity. As a result, film stretching induces drastic changes in both the spectral position and intensity of the plasmonic-enhanced FP resonances due to the simultaneous cavity thickness reduction and cavity wrinkle flattening, thus increasing the cavity finesse. These optomechanical effects are exploited to demonstrate new strain-sensing approaches, achieving a strain detection limit of 0.006%, i.e., 16-fold lower than current optical strain-detection schemes. © 2022 Wiley-VCH GmbH

View abstract

2021

Direct Evidence of a Graded Magnetic Interface in Bimagnetic Core/Shell Nanoparticles Using Electron Magnetic Circular Dichroism (EMCD)
Del-Pozo-Bueno D., Varela M., Estrader M., López-Ortega A., Roca A.G., Nogués J., Peiró F., Estradé S. Nano Letters; 21 (16): 6923 - 6930. 2021. 10.1021/acs.nanolett.1c02089. IF: 11.189

Interfaces play a crucial role in composite magnetic materials and particularly in bimagnetic core/shell nanoparticles. However, resolving the microscopic magnetic structure of these nanoparticles is rather complex. Here, we investigate the local magnetization of antiferromagnetic/ferrimagnetic FeO/Fe3O4 core/shell nanocubes by electron magnetic circular dichroism (EMCD). The electron energy-loss spectroscopy (EELS) compositional analysis of the samples shows the presence of an oxidation gradient at the interface between the FeO core and the Fe3O4 shell. The EMCD measurements show that the nanoparticles are composed of four different zones with distinct magnetic moment in a concentric, onion-type, structure. These magnetic areas correlate spatially with the oxidation and composition gradient with the magnetic moment being largest at the surface and decreasing toward the core. The results show that the combination of EELS compositional mapping and EMCD can provide very valuable information on the inner magnetic structure and its correlation to the microstructure of magnetic nanoparticles. © 2021 The Authors. Published by American Chemical Society.

View abstract
Mechanochromic Detection for Soft Opto-Magnetic Actuators
Güell-Grau P., Escudero P., Perdikos F.G., López-Barbera J.F., Pascual-Izarra C., Villa R., Nogués J., Sepúlveda B., Alvarez M. ACS Applied Materials and Interfaces; 13 (40): 47871 - 47881. 2021. 10.1021/acsami.1c11710. IF: 9.229

New multi-stimuli responsive materials are required in smart systems applications to overcome current limitations in remote actuation and to achieve versatile operation in inaccessible environments. The incorporation of detection mechanisms to quantify in real time the response to external stimuli is crucial for the development of automated systems. Here, we present the first wireless opto-magnetic actuator with mechanochromic response. The device, based on a nanostructured-iron (Fe) layer transferred onto suspended elastomer structures with a periodically corrugated backside, can be actuated both optically (in a broadband spectral range) and magnetically. The combined opto-magnetic stimulus can accurately modulate the mechanical response (strength and direction) of the device. The structural coloration generated at the corrugated back surface enables to easily map and quantify, in 2D, the mechanical deflections by analyzing in real time the hue changes of images taken using a conventional RGB smartphone camera, with a precision of 0.05°. We demonstrate the independent and synergetic optical and magnetic actuation and detection with a detection limit of 1.8 mW·cm-2 and 0.34 mT, respectively. The simple operation, versatility, and cost-effectiveness of the wireless multiactuated device with highly sensitive mechanochromic mapping paves the way to a new generation of wirelessly controlled smart systems. © 2021 American Chemical Society.

View abstract
Probing the meta-stability of oxide core/shell nanoparticle systems at atomic resolution
Roldan M.A., Mayence A., López-Ortega A., Ishikawa R., Salafranca J., Estrader M., Salazar-Alvarez G., Dolors Baró M., Nogués J., Pennycook S.J., Varela M. Chemical Engineering Journal; 405 (126820) 2021. 10.1016/j.cej.2020.126820. IF: 13.273

Hybrid nanoparticles allow exploiting the interplay of confinement, proximity between different materials and interfacial effects. However, to harness their properties an in-depth understanding of their (meta)stability and interfacial characteristics is crucial. This is especially the case of nanosystems based on functional oxides working under reducing conditions, which may severely impact their properties. In this work, the in-situ electron-induced selective reduction of Mn3O4 to MnO is studied in magnetic Fe3O4/Mn3O4 and Mn3O4/Fe3O4 core/shell nanoparticles by means of high-resolution scanning transmission electron microscopy combined with electron energy-loss spectroscopy. Such in-situ transformation allows mimicking the actual processes in operando environments. A multi-stage image analysis using geometric phase analysis combined with particle image velocity enables direct monitoring of the relationship between structure, chemical composition and strain relaxation during the Mn3O4 reduction. In the case of Fe3O4/Mn3O4 core/shell the transformation occurs smoothly without the formation of defects. However, for the inverse Mn3O4/Fe3O4 core/shell configuration the electron beam-induced transformation occurs in different stages that include redox reactions and void formation followed by strain field relaxation via formation of defects. This study highlights the relevance of understanding the local dynamics responsible for changes in the particle composition in order to control stability and, ultimately, macroscopic functionality. © 2020 Elsevier B.V.

View abstract
Ultrabroadband light absorbing Fe/polymer flexible metamaterial for soft opto-mechanical devices
Güell-Grau P., Pi F., Villa R., Nogués J., Alvarez M., Sepúlveda B. Applied Materials Today; 23 (101052) 2021. 10.1016/j.apmt.2021.101052. IF: 10.041

Ultrabroadband light absorbers are attracting increasing interest for applications in energy harvesting, photodetection, self-regulated devices or soft robotics. However, current absorbers show detrimental insufficient absorption spectral range, or light angle and polarization dependence. Here we show that the unexplored optical properties of highly-damped plasmonic materials combined with the infrared absorption of thin polymer films enable developing ultrabroadband light-absorbing soft metamaterials. The developed metamaterial, composed of a nanostructured Fe layer mechanically coupled to a thin polydimethylsiloxane (PDMS) film, shows unprecedented ultrabroadband and angle-independent optical absorption (averaging 84% within 300–18000 nm). The excellent photothermal efficiency and large thermal-expansion mismatch of the metamaterial is efficiently transformed into large mechanical deflections, which we exploit to show an artificial iris that self-regulates the transmitted light power from the ultraviolet to the long-wave infrared, an untethered light-controlled mechanical gripper and a light-triggered electrical switch. © 2021 The Authors

View abstract

2020

Highly reduced ecotoxicity of ZnO-based micro/nanostructures on aquatic biota: Influence of architecture, chemical composition, fixation, and photocatalytic efficiency
Serrà A., Zhang Y., Sepúlveda B., Gómez E., Nogués J., Michler J., Philippe L. Water Research; 169 (115210) 2020. 10.1016/j.watres.2019.115210. IF: 9.130

Developing efficient sunlight photocatalysts with enhanced photocorrosion resistance and minimal ecotoxicological effects on aquatic biota is critical to combat water contamination. Here, the role of chemical composition, architecture, and fixation on the ecotoxicological effects on microalgae of different ZnO and ZnO@ZnS based water decontamination photocatalysts was analyzed in depth. In particular, the ecotoxicological effects of films, nanoparticles and biomimetic micro/nano-ferns were carefully assessed by correlating the algae's viability to the Zn(II) release, the photocatalyst–microalgae interaction, and the production of reactive oxygen species (ROS). The results showed a drastic improvement in algal viability for supported ZnO@ZnS core@shell micro/nanoferns, as their ecotoxicity after 96 h light exposure was significantly lower (3.7–10.0% viability loss) compared to the ZnO films (18.4–35.5% loss), ZnO micro/nanoferns (28.5–53.5% loss), ZnO nanoparticles (48.3–91.7% loss) or ZnO@ZnS nanoparticles (8.6–19.2% loss) for catalysts concentrations ranging from 25 mg L−1 to 400 mg L−1. In particular, the ZnO@ZnS micro/nanoferns with a concentration of 400 mg L−1 exhibited excellent photocatalytic efficiency to mineralize a multi-pollutant solution (81.4 ± 0.3% mineralization efficiency after 210 min under UV-filtered visible light irradiation) and minimal photocorrosion (<5% of photocatalyst dissolution after 96 h of UV-filtered visible light irradiation). Remarkably, the ZnO@ZnS micro/nanoferns showed lower loss of algal viability (9.8 ± 1.1%) after 96 h of light exposure, with minimal reduction in microalgal biomass (9.1 ± 1.0%), as well as in the quantity of chlorophyll-a (9.5 ± 1.0%), carotenoids (8.6 ± 0.9%) and phycocyanin (5.6 ± 0.6%). Altogether, the optimized ZnO@ZnS core@shell micro/nanoferns represent excellent ecofriendly photocatalysts for water remediation in complex media, as they combine enhanced sunlight remediation efficiency, minimal adverse effects on biological microorganisms, high reusability and easy recyclability. © 2019 Elsevier Ltd

View abstract
Hybrid Ni@ZnO@ZnS-Microalgae for Circular Economy: A Smart Route to the Efficient Integration of Solar Photocatalytic Water Decontamination and Bioethanol Production
Serrà A., Artal R., García-Amorós J., Sepúlveda B., Gómez E., Nogués J., Philippe L. Advanced Science; 7 (3, 1902447) 2020. 10.1002/advs.201902447. IF: 15.840

Water remediation and development of carbon-neutral fuels are a priority for the evermore industrialized society. The answer to these challenges should be simple, sustainable, and inexpensive. Thus, biomimetic-inspired circular and holistic processes combing water remediation and biofuel production can be an appealing concept to deal with these global issues. A simple circular approach using helical Spirulina platensis microalgae as biotemplates to synthesize Ni@ZnO@ZnS photocatalysts for efficient solar water decontamination and bioethanol production during the recycling process is presented. Under solar irradiation, the Ni@ZnO@ZnS-Spirulina photocatalyst exhibits enhanced activity (mineralization efficiency >99%) with minimal photocorrosion and excellent reusability. At the end of its effective lifetime for water remediation, the microalgae skeleton (mainly glycogen and glucose) of the photocatalyst is recycled to directly produce bioethanol by simultaneous saccharification and fermentation process. An outstanding ethanol yield of 0.4 L kg−1, which is similar to the highest yield obtained from oxygenic photosynthetic microorganisms, is obtained. Thus, the entire process allows effective solar photocatalytic water remediation and bioethanol production at room temperature using simple and easily scalable procedures that simultaneously fixes carbon dioxide, thereby constituting a zero-carbon-emission circular process. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

View abstract
Local manipulation of metamagnetism by strain nanopatterning
Foerster M., Menéndez E., Coy E., Quintana A., Gómez-Olivella C., Esqué De Los Ojos D., Vallcorba O., Frontera C., Aballe L., Nogués J., Sort J., Fina I. Materials Horizons; 7 (8): 2056 - 2062. 2020. 10.1039/d0mh00601g. IF: 12.319

Among metamagnetic materials, FeRh alloys are technologically appealing due to their uncommon antiferromagnetic-to-ferromagnetic metamagnetic transition which occurs at a temperature T∗ just above room temperature. Here, a controlled increase of T∗ (ΔT∗ ∼ 20 °C) is induced in pre-selected regions of FeRh films via mechanical strain nanopatterning. Compressive stresses generated at the vicinity of pre-defined nanoindentation imprints cause a local reduction of the FeRh crystallographic unit cell parameter, which leads to an increase of T∗ in these confined micro-/nanometric areas. This enhances the stability of the antiferromagnetic phase in these localized regions. Remarkably, generation of periodic arrays of nanopatterned features also allows modifying the overall magnetic and electric transport properties across large areas of the FeRh films. This approach is highly appealing for the design of new memory architectures or other AFM-spintronic devices. © The Royal Society of Chemistry.

View abstract
Simultaneous individual and dipolar collective properties in binary assemblies of magnetic nanoparticles
Sánchez E.H., Vasilakaki M., Lee S.S., Normile P.S., Muscas G., Murgia M., Andersson M.S., Singh G., Mathieu R., Nordblad P., Ricci P.C., Peddis D., Trohidou K.N., Nogués J., De Toro J.A. Chemistry of Materials; 32 (3): 969 - 981. 2020. 10.1021/acs.chemmater.9b03268. IF: 9.567

Applications based on aggregates of magnetic nanoparticles are becoming increasingly widespread, ranging from hyperthermia to magnetic recording. However, although some uses require collective behavior, others need a more individual-like response, the conditions leading to either of these behaviors are still poorly understood. Here, we use nanoscale-uniform binary random dense mixtures with different proportions of oxide magnetic nanoparticles with low/high anisotropy as a valuable tool to explore the crossover from individual to collective behavior. Two different anisotropy scenarios have been studied in two series of binary compacts: M1, comprising maghemite (γ-Fe2O3) nanoparticles of different sizes (9.0 nm/11.5 nm) with barely a factor of 2 between their anisotropy energies, and M2, mixing equally sized pure maghemite (low-anisotropy) and Co-doped maghemite (high-anisotropy) nanoparticles with a large difference in anisotropy energy (ratio > 8). Interestingly, while the M1 series exhibits collective behavior typical of strongly coupled dipolar systems, the M2 series presents a more complex scenario where different magnetic properties resemble either "individual-like"or "collective", crucially emphasizing that the collective character must be ascribed to specific properties and not to the system as a whole. The strong differences between the two series offer new insight (systematically ratified by simulations) into the subtle interplay between dipolar interactions, local anisotropy and sample heterogeneity to determine the behavior of dense assemblies of magnetic nanoparticles. © 2020 American Chemical Society.

View abstract
Voltage-driven motion of nitrogen ions: a new paradigm for magneto-ionics
de Rojas J., Quintana A., Lopeandía A., Salguero J., Muñiz B., Ibrahim F., Chshiev M., Nicolenco A., Liedke M.O., Butterling M., Wagner A., Sireus V., Abad L., Jensen C.J., Liu K., Nogués J., Costa-Krämer J.L., Menéndez E., Sort J. Nature Communications; 11 (1, 5871) 2020. 10.1038/s41467-020-19758-x. IF: 12.121

Magneto-ionics, understood as voltage-driven ion transport in magnetic materials, has largely relied on controlled migration of oxygen ions. Here, we demonstrate room-temperature voltage-driven nitrogen transport (i.e., nitrogen magneto-ionics) by electrolyte-gating of a CoN film. Nitrogen magneto-ionics in CoN is compared to oxygen magneto-ionics in Co3O4. Both materials are nanocrystalline (face-centered cubic structure) and show reversible voltage-driven ON-OFF ferromagnetism. In contrast to oxygen, nitrogen transport occurs uniformly creating a plane-wave-like migration front, without assistance of diffusion channels. Remarkably, nitrogen magneto-ionics requires lower threshold voltages and exhibits enhanced rates and cyclability. This is due to the lower activation energy for ion diffusion and the lower electronegativity of nitrogen compared to oxygen. These results may open new avenues in applications such as brain-inspired computing or iontronics in general. © 2020, The Author(s).

View abstract

2019

Highly active ZnO-based biomimetic fern-like microleaves for photocatalytic water decontamination using sunlight
Serrà A., Zhang Y., Sepúlveda B., Gómez E., Nogués J., Michler J., Philippe L. Applied Catalysis B: Environmental; 248: 129 - 146. 2019. 10.1016/j.apcatb.2019.02.017. IF: 14.229

Here we present the highly enhanced sunlight photocatalytic efficiency and photocorrosion resistance of biomimetic ZnO-modified micro/nanofern fractal architectures, which are synthesized by using a novel, simple, inexpensive and green electrochemical deposition approach in high stirring conditions. Such fern-like hierarchical structures simultaneously combine enhanced angle independent light trapping and surface/bulk modifications of the ZnO morphology to drastically increase: i) the light trapping and absorption in the visible near-infrared range, and ii) the surface to volume ratio of the architecture. This combination is crucial for boosting the sunlight photocatalytic efficiency. To modulate the electronic properties for extending the operation of the ZnO photocatalysts into the visible domain we have used three different modification approaches: sulfidation (leading to a ZnS shell), Ag decoration, and Ni-doping. The different ZnO-modified bioinspired fern-like fractal structures have been used to demonstrate their efficiency in the photodegradation and photoremediation of three different persistent organic pollutants –methylene blue, 4-nitrophenol, and Rhodamine B – under UV light, simulated and natural UV-filtered sunlight. Remarkably, the ZnO@ZnS core@shell structures exhibited an outstanding photocatalytic activity compared to the pristine ZnO catalyst, with over 6-fold increase in the pollutant degradation rate when using solar light. In fact, the catalytic performance of the ZnO@ZnS micro/nanoferns for the photoremediation of persistent organic pollutants is comparable to or better than the most competitive state-of-the-art ZnO photocatalysts, but showing a negligible photocorrosion. Ag-decorated ZnO, and Ni-doped ZnO exhibited similar excellent visible-sunlight photodegradation efficiency. Although the Ni-doped photocatalysts showed a relatively poor photocorrosion resistance, it was acceptable for Ag-decorated ZnO. Therefore, the easy fabrication and the capacity to drastically enhance the sunlight photocatalytic efficiency of the ZnO@ZnS bioinspired micro/nanoferns, together with their practically negligible photocorrosion and simple recyclability in terms of non-catalyst poisoning, makes them very promising photocatalysts for water remediation. © 2019 Elsevier B.V.

View abstract
Precise Size Control of the Growth of Fe3O4 Nanocubes over a Wide Size Range Using a Rationally Designed One-Pot Synthesis
Muro-Cruces J., Roca A.G., López-Ortega A., Fantechi E., Del-Pozo-Bueno D., Estradé S., Peiró F., Sepúlveda B., Pineider F., Sangregorio C., Nogues J. ACS Nano; 2019. 10.1021/acsnano.9b01281. IF: 13.903

The physicochemical properties of spinel oxide magnetic nanoparticles depend critically on both their size and shape. In particular, spinel oxide nanocrystals with cubic morphology have shown superior properties in comparison to their spherical counterparts in a variety of fields, like, for example, biomedicine. Therefore, having an accurate control over the nanoparticle shape and size, while preserving the crystallinity, becomes crucial for many applications. However, despite the increasing interest in spinel oxide nanocubes there are relatively few studies on this morphology due to the difficulty to synthesize perfectly defined cubic nanostructures, especially below 20 nm. Here we present a rationally designed synthesis pathway based on the thermal decomposition of iron(III) acetylacetonate to obtain high quality nanocubes over a wide range of sizes. This pathway enables the synthesis of monodisperse Fe3O4 nanocubes with edge length in the 9-80 nm range, with excellent cubic morphology and high crystallinity by only minor adjustments in the synthesis parameters. The accurate size control provides evidence that even 1-2 nm size variations can be critical in determining the functional properties, for example, for improved nuclear magnetic resonance T2 contrast or enhanced magnetic hyperthermia. The rationale behind the changes introduced in the synthesis procedure (e.g., the use of three solvents or adding Na-oleate) is carefully discussed. The versatility of this synthesis route is demonstrated by expanding its capability to grow other spinel oxides such as Co-ferrites, Mn-ferrites, and Mn3O4 of different sizes. The simplicity and adaptability of this synthesis scheme may ease the development of complex oxide nanocubes for a wide variety of applications. © 2019 American Chemical Society.

View abstract
Zinc blende and wurtzite CoO polymorph nanoparticles: Rational synthesis and commensurate and incommensurate magnetic order
Golosovsky I.V., Estrader M., López-Ortega A., Roca A.G., López-Conesa L., Del Corro E., Estradé S., Peiró F., Puente-Orench I., Nogués J. Applied Materials Today; 16: 322 - 331. 2019. 10.1016/j.apmt.2019.06.005. IF: 8.013

On the nanoscale, CoO can have different polymorph crystal structures, zinc blende and wurtzite, apart from rock salt, which is the stable one in bulk. However, the magnetic structures of the zinc blende and wurtzite phases remain virtually unexplored. Here we discuss some of the main parameters controlling the growth of the CoO wurtzite and zinc blende polymorphs by thermal decomposition of cobalt (II) acetylacetonate. In addition, we present a detailed neutron diffraction study of oxygen deficient CoO (CoO0.70–0.75) nanoparticles with zinc blende (∼15 nm) and wurtzite (∼30 nm) crystal structures to unravel their magnetic order and its temperature evolution. The magnetic order of the zinc blende nanoparticles is antiferromagnetic and appears at the Néel temperature TN ∼ 203 K. It corresponds to the 3rd type of magnetic ordering in a face-centered cubic lattice with magnetic moments aligned along a cube edge. The magnetic structure in the wurtzite nanoparticles turned out to be rather complex with two perpendicular components. One component is incommensurate, of the longitudinal spin wave type, with the magnetic moments confined in the ab-plane. In the perpendicular direction, this magnetic order is uncorrelated, forming quasi-two-dimensional magnetic layers. The component of the magnetic moment, aligned along the hexagonal axis, is commensurate and corresponds to the antiferromagnetic order known as the 2nd type in a wurtzite structure. The Néel temperature of wurtzite phase is estimated to be ∼109 K. The temperature dependence of the magnetic reflections confirms the reduced dimensionality of the incommensurate magnetic order. Incommensurate magnetic structures in nanoparticles are an unusual phenomenon and in the case of wurtzite CoO it is probably caused by structural defects (e.g., vacancies, strains and stacking faults). © 2019 Elsevier Ltd

View abstract

2018

Atomic-Scale Determination of Cation Inversion in Spinel-Based Oxide Nanoparticles
Torruella P., Ruiz-Caridad A., Walls M., Roca A.G., López-Ortega A., Blanco-Portals J., López-Conesa L., Nogués J., Peiró F., Estradé S. Nano Letters; 18 (9): 5854 - 5861. 2018. 10.1021/acs.nanolett.8b02524. IF: 12.080

The atomic structure of nanoparticles can be easily determined by transmission electron microscopy. However, obtaining atomic-resolution chemical information about the individual atomic columns is a rather challenging endeavor. Here, crystalline monodispersed spinel Fe3O4/Mn3O4 core-shell nanoparticles have been thoroughly characterized in a high-resolution scanning transmission electron microscope. Electron energy-loss spectroscopy (EELS) measurements performed with atomic resolution allow the direct mapping of the Mn2+/Mn3+ ions in the shell and the Fe2+/Fe3+ in the core structure. This enables a precise understanding of the core-shell interface and of the cation distribution in the crystalline lattice of the nanoparticles. Considering how the different oxidation states of transition metals are reflected in EELS, two methods of performing a local evaluation of the cation inversion in spinel lattices are introduced. Both methods allow the determination of the inversion parameter in the iron oxide core and manganese oxide shell, as well as detecting spatial variations in this parameter, with atomic resolution. X-ray absorption measurements on the whole sample confirm the presence of cation inversion. These results present a significant advance toward a better correlation of the structural and functional properties of nanostructured spinel oxides. © 2018 American Chemical Society.

View abstract
Coercivity Modulation in Fe–Cu Pseudo-Ordered Porous Thin Films Controlled by an Applied Voltage: A Sustainable, Energy-Efficient Approach to Magnetoelectrically Driven Materials
Dislaki E., Robbennolt S., Campoy-Quiles M., Nogués J., Pellicer E., Sort J. Advanced Science; 5 (8, 1800499) 2018. 10.1002/advs.201800499. IF: 12.441

Fe–Cu films with pseudo-ordered, hierarchical porosity are prepared by a simple, two-step procedure that combines colloidal templating (using sub-micrometer-sized polystyrene spheres) with electrodeposition. The porosity degree of these films, estimated by ellipsometry measurements, is as high as 65%. The resulting magnetic properties can be controlled at room temperature using an applied electric field generated through an electric double layer in an anhydrous electrolyte. This material shows a remarkable 25% voltage-driven coercivity reduction upon application of negative voltages, with excellent reversibility when a positive voltage is applied, and a short recovery time. The pronounced reduction of coercivity is mainly ascribed to electrostatic charge accumulation at the surface of the porous alloy, which occurs over a large fraction of the electrodeposited material due to its high surface-area-to-volume ratio. The emergence of a hierarchical porosity is found to be crucial because it promotes the infiltration of the electrolyte into the structure of the film. The observed effects make this material a promising candidate to boost energy efficiency in magnetoelectrically actuated devices. © 2018 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

View abstract
Combining X-Ray Whole Powder Pattern Modeling, Rietveld and Pair Distribution Function Analyses as a Novel Bulk Approach to Study Interfaces in Heteronanostructures: Oxidation Front in FeO/Fe3O4 Core/Shell Nanoparticles as a Case Study
Ichikawa R.U., Roca A.G., López-Ortega A., Estrader M., Peral I., Turrillas X., Nogués J. Small; 14 (30, 1800804) 2018. 10.1002/smll.201800804. IF: 9.598

Understanding the microstructure in heterostructured nanoparticles is crucial to harnessing their properties. Although microscopy is ideal for this purpose, it allows for the analysis of only a few nanoparticles. Thus, there is a need for structural methods that take the whole sample into account. Here, a novel bulk-approach based on the combined analysis of synchrotron X-ray powder diffraction with whole powder pattern modeling, Rietveld and pair distribution function is presented. The microstructural temporal evolution of FeO/Fe3O4 core/shell nanocubes is studied at different time intervals. The results indicate that a two-phase approach (FeO and Fe3O4) is not sufficient to successfully fit the data and two additional interface phases (FeO and Fe3O4) are needed to obtain satisfactory fits, i.e., an onion-type structure. The analysis shows that the Fe3O4 phases grow to some extent (≈1 nm) at the expense of the FeO core. Moreover, the FeO core progressively changes its stoichiometry to accommodate more oxygen. The temporal evolution of the parameters indicates that the structure of the FeO/Fe3O4 nanocubes is rather stable, although the exact interface structure slightly evolves with time. This approach paves the way for average studies of interfaces in different kinds of heterostructured nanoparticles, particularly in cases where spectroscopic methods have some limitations. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

View abstract
Enhanced Ultrafast Nonlinear Optical Response in Ferrite Core/Shell Nanostructures with Excellent Optical Limiting Performance
Perumbilavil S., López-Ortega A., Tiwari G.K., Nogués J., Endo T., Philip R. Small; 14 (6, 1701001) 2018. 10.1002/smll.201701001. IF: 9.598

Nonlinear optical nanostructured materials are gaining increased interest as optical limiters for various applications, although many of them suffer from reduced efficiencies at high-light fluences due to photoinduced deterioration. The nonlinear optical properties of ferrite core/shell nanoparticles showing their robustness for ultrafast optical limiting applications are reported. At 100 fs ultrashort laser pulses the effective two-photon absorption (2PA) coefficient shows a nonmonotonic dependence on the shell thickness, with a maximum value obtained for thin shells. In view of the local electric field confinement, this indicates that core/shell is an advantageous morphology to improve the nonlinear optical parameters, exhibiting excellent optical limiting performance with effective 2PA coefficients in the range of 10−12 cm W−1 (100 fs excitation), and optical limiting threshold fluences in the range of 1.7 J cm−2. These values are comparable to or better than most of the recently reported optical limiting materials. The quality of the open aperture Z-scan data recorded from repeat measurements at intensities as high as 35 TW cm−2, indicates their considerably high optical damage thresholds in a toluene dispersion, ensuring their robustness in practical applications. Thus, the high photostability combined with the remarkable nonlinear optical properties makes these nanoparticles excellent candidates for ultrafast optical limiting applications. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

View abstract
Large Magnetoelectric Effects in Electrodeposited Nanoporous Microdisks Driven by Effective Surface Charging and Magneto-Ionics
Navarro-Senent C., Fornell J., Isarain-Chávez E., Quintana A., Menéndez E., Foerster M., Aballe L., Weschke E., Nogués J., Pellicer E., Sort J. ACS Applied Materials and Interfaces; 10 (51): 44897 - 44905. 2018. 10.1021/acsami.8b17442. IF: 8.097

A synergetic approach to enhance magnetoelectric effects (i.e., control of magnetism with voltage) and improve energy efficiency in magnetically actuated devices is presented. The investigated material consists of an ordered array of Co-Pt microdisks, in which nanoporosity and partial oxidation are introduced during the synthetic procedure to synergetically boost the effects of electric field. The microdisks are grown by electrodeposition from an electrolyte containing an amphiphilic polymeric surfactant. The bath formulation is designed to favor the incorporation of oxygen in the form of cobalt oxide. A pronounced reduction of coercivity (88%) and a remarkable increase of Kerr signal amplitude (60%) are observed at room temperature upon subjecting the microdisks to negative voltages through an electrical double layer. These large voltage-induced changes in the magnetic properties of the microdisks are due to (i) the high surface-area-to-volume ratio with ultranarrow pore walls (sub-10 nm) that promote enhanced electric charge accumulation and (ii) magneto-ionic effects, where voltage-driven O 2- migration promotes a partial reduction of CoO to Co at room temperature. This simple and versatile procedure to fabricate patterned "nano-in-micro" magnetic motifs with adjustable voltage-driven magnetic properties is very appealing for energy-efficient magnetic recording systems and other magnetoelectronic devices. © Copyright © 2018 American Chemical Society.

View abstract
Magnetically amplified photothermal therapies and multimodal imaging with magneto-plasmonic nanodomes
Li Z., Aranda-Ramos A., Güell-Grau P., Tajada J.L., Pou-Macayo L., Lope Piedrafita S., Pi F., G. Roca A., Baró M.D., Sort J., Nogués C., Nogués J., Sepúlveda B. Applied Materials Today; 12: 430 - 440. 2018. 10.1016/j.apmt.2018.07.008. IF: 0.000

Nanotherapies require new ways for controlling and improving the delivery of the therapeutic agents to the site of action to maximize their efficacy and minimize the side effects. This control is particularly relevant in photothermal treatments to reduce the required light intensity and amount of injected nanoparticles, and to minimize necrotic cell deaths. Here we present a novel concept for multifunctional nanobiomedical agents: magneto-plasmonic (MP) nanodomes for magnetically guided and amplified photothermal therapies and as contrast agents for multimodal imaging. The MP nanodomes are composed of a Fe/Au bilayer semi-shell deposited on a 100 nm diameter fluorescent polystyrene nanosphere, which gather a unique combination of straightforward functionalization, high colloidal stability, very strong ferromagnetic behavior and intense optical absorption efficiency in the near infrared. We show that the photothermal conversion efficiency of the Fe/Au nanodomes with high Fe ratios is substantially larger than pure plasmonic Au nanodomes and the state-of-art plasmonic nanoheaters, i.e. Au nanorods and nanoshells, by merging strong optical absorption, minimized scattering and low optical anisotropy. Remarkably, the effective magnetophoretic concentration of the Fe/Au nanodomes at the illumination region enables large local increase of the optically induced temperature rise. The Fe semishell also provides very intense T2 contrast in nuclear magnetic resonance, which is at least 15-fold larger per particle than commercial iron oxide contrast agents. Moreover, the fluorescent polystyrene nanosphere and the Au semishell integrate valuable fluorescent and X-ray contrasts, respectively, which we have used to assess the nanodomes internalization by cancer cells. The MP nanodomes are nontoxic to cells even in the case of magnetophoretic local enrichment with initially high particle concentration (100 μg/mL). Remarkably, we demonstrate amplified local photothermal treatments by the magnetic enrichment of the nanodomes at the illumination region, which enables reaching nearly 100% reduction of cell viability with low particle concentration (10 μg/mL) and mild NIR laser intensity (5 W/cm2). These results highlight the high potential of MP nanodomes for magnetically guided and amplified photothermal therapies. © 2018 Elsevier Ltd

View abstract
Simultaneous Local Heating/Thermometry Based on Plasmonic Magnetochromic Nanoheaters
Li Z., Lopez-Ortega A., Aranda-Ramos A., Tajada J.L., Sort J., Nogues C., Vavassori P., Nogues J., Sepulveda B. Small; 14 (24, 1800868) 2018. 10.1002/smll.201800868. IF: 9.598

A crucial challenge in nanotherapies is achieving accurate and real-time control of the therapeutic action, which is particularly relevant in local thermal therapies to minimize healthy tissue damage and necrotic cell deaths. Here, a nanoheater/thermometry concept is presented based on magnetoplasmonic (Co/Au or Fe/Au) nanodomes that merge exceptionally efficient plasmonic heating and simultaneous highly sensitive detection of the temperature variations. The temperature detection is based on precise optical monitoring of the magnetic-induced rotation of the nanodomes in solution. It is shown that the phase lag between the optical signal and the driving magnetic field can be used to detect viscosity variations around the nanodomes with unprecedented accuracy (detection limit 0.0016 mPa s, i.e., 60-fold smaller than state-of-the-art plasmonic nanorheometers). This feature is exploited to monitor the viscosity reduction induced by optical heating in real-time, even in highly inhomogeneous cell dispersions. The magnetochromic nanoheater/thermometers show higher optical stability, much higher heating efficiency and similar temperature detection limits (0.05 °C) compared to state-of-the art luminescent nanothermometers. The technological interest is also boosted by the simpler and lower cost temperature detection system, and the cost effectiveness and scalability of the nanofabrication process, thereby highlighting the biomedical potential of this nanotechnology. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

View abstract
Tunable Magnetism in Nanoporous CuNi Alloys by Reversible Voltage-Driven Element-Selective Redox Processes
Quintana A., Menéndez E., Isarain-Chávez E., Fornell J., Solsona P., Fauth F., Baró M.D., Nogués J., Pellicer E., Sort J. Small; 14 (21, 1704396) 2018. 10.1002/smll.201704396. IF: 9.598

Voltage-driven manipulation of magnetism in electrodeposited 200 nm thick nanoporous single-phase solid solution Cu20Ni80 (at%) alloy films (with sub 10 nm pore size) is accomplished by controlled reduction-oxidation (i.e., redox) processes in a protic solvent, namely 1 m NaOH aqueous solution. Owing to the selectivity of the electrochemical processes, the oxidation of the CuNi film mainly occurs on the Cu counterpart of the solid solution, resulting in a Ni-enriched alloy. As a consequence, the magnetic moment at saturation significantly increases (up to 33% enhancement with respect to the as-prepared sample), while only slight changes in coercivity are observed. Conversely, the reduction process brings Cu back to its metallic state and, remarkably, it becomes alloyed to Ni again. The reported phenomenon is fully reversible, thus allowing for the precise adjustment of the magnetic properties of this system through the sign and amplitude of the applied voltage. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

View abstract
Unravelling the Elusive Antiferromagnetic Order in Wurtzite and Zinc Blende CoO Polymorph Nanoparticles
Roca A.G., Golosovsky I.V., Winkler E., López-Ortega A., Estrader M., Zysler R.D., Baró M.D., Nogués J. Small; 14 (15, 1703963) 2018. 10.1002/smll.201703963. IF: 9.598

Although cubic rock salt-CoO has been extensively studied, the magnetic properties of the main nanoscale CoO polymorphs (hexagonal wurtzite and cubic zinc blende structures) are rather poorly understood. Here, a detailed magnetic and neutron diffraction study on zinc blende and wurtzite CoO nanoparticles is presented. The zinc blende-CoO phase is antiferromagnetic with a 3rd type structure in a face-centered cubic lattice and a Néel temperature of TN (zinc-blende) ≈225 K. Wurtzite-CoO also presents an antiferromagnetic order, TN (wurtzite) ≈109 K, although much more complex, with a 2nd type order along the c-axis but an incommensurate order along the y-axis. Importantly, the overall magnetic properties are overwhelmed by the uncompensated spins, which confer the system a ferromagnetic-like behavior even at room temperature. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

View abstract
Voltage-Controlled ON-OFF Ferromagnetism at Room Temperature in a Single Metal Oxide Film
Quintana A., Menéndez E., Liedke M.O., Butterling M., Wagner A., Sireus V., Torruella P., Estradé S., Peiró F., Dendooven J., Detavernier C., Murray P.D., Gilbert D.A., Liu K., Pellicer E., Nogues J., Sort J. ACS Nano; 2018. 10.1021/acsnano.8b05407. IF: 13.709

Electric-field-controlled magnetism can boost energy efficiency in widespread applications. However, technologically, this effect is facing important challenges: mechanical failure in strain-mediated piezoelectric/magnetostrictive devices, dearth of room-temperature multiferroics, or stringent thickness limitations in electrically charged metallic films. Voltage-driven ionic motion (magneto-ionics) circumvents most of these drawbacks while exhibiting interesting magnetoelectric phenomena. Nevertheless, magneto-ionics typically requires heat treatments and multicomponent heterostructures. Here we report on the electrolyte-gated and defect-mediated O and Co transport in a Co3O4 single layer which allows for room-temperature voltage-controlled ON-OFF ferromagnetism (magnetic switch) via internal reduction/oxidation processes. Negative voltages partially reduce Co3O4 to Co (ferromagnetism: ON), resulting in graded films including Co- and O-rich areas. Positive bias oxidizes Co back to Co3O4 (paramagnetism: OFF). This electric-field-induced atomic-scale reconfiguration process is compositionally, structurally, and magnetically reversible and self-sustained, since no oxygen source other than the Co3O4 itself is required. This process could lead to electric-field-controlled device concepts for spintronics. © 2018 American Chemical Society.

View abstract

2017

Lateral Magnetically Modulated Multilayers by Combining Ion Implantation and Lithography
Menéndez E., Modarresi H., Petermann C., Nogués J., Domingo N., Liu H., Kirby B.J., Mohd A.S., Salhi Z., Babcock E., Mattauch S., Van Haesendonck C., Vantomme A., Temst K. Small; 13 (11, 1603465) 2017. 10.1002/smll.201603465. IF: 8.643

The combination of lithography and ion implantation is demonstrated to be a suitable method to prepare lateral multilayers. A laterally, compositionally, and magnetically modulated microscale pattern consisting of alternating Co (1.6 µm wide) and Co-CoO (2.4 µm wide) lines has been obtained by oxygen ion implantation into a lithographically masked Au-sandwiched Co thin film. Magnetoresistance along the lines (i.e., current and applied magnetic field are parallel to the lines) reveals an effective positive giant magnetoresistance (GMR) behavior at room temperature. Conversely, anisotropic magnetoresistance and GMR contributions are distinguished at low temperature (i.e., 10 K) since the O-implanted areas become exchange coupled. This planar GMR is principally ascribed to the spatial modulation of coercivity in a spring-magnet-type configuration, which results in 180° Néel extrinsic domain walls at the Co/Co-CoO interfaces. The versatility, in terms of pattern size, morphology, and composition adjustment, of this method offers a unique route to fabricate planar systems for, among others, spintronic research and applications. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

View abstract
Magnetically-actuated mesoporous nanowires for enhanced heterogeneous catalysis
Serrà A., Grau S., Gimbert-Suriñach C., Sort J., Nogués J., Vallés E. Applied Catalysis B: Environmental; 217: 81 - 91. 2017. 10.1016/j.apcatb.2017.05.071. IF: 9.446

We study the optimization of the catalytic properties of entirely magnetic Co–Pt compact and mesoporous nanowires of different diameters (25–200 nm) by using magnetic actuation. The nanowires are a single-entity, robust, magnetic-catalyst with a huge catalytically-active surface area. We show that apart from conventional parameters, like the size and morphology of the nanowires, other factors can be optimized to enhance their catalytic activity. In particular, given the magnetic character of the nanowires, rotating magnetic fields are a very powerful approach to boost the performance of the catalyst. In particular, the magnetic field induces them to act as nano-stirrers, improving the local flow of material towards the active sites of the catalyst. We demonstrate the versatility of the procedure by optimizing (i) the degradation of different types of pollutants (4-nitrophenol and methylene blue) and (ii) hydrogen production. For example, by using as little as 0.1 mg mL−1 of 25 nm wide Co–Pt mesoporous nanowires (with ∼3 nm pore size) as catalysts, kinetic normalized constants knor as high as 20,667 and 21,750 s−1 g−1 for 4-nitrophenol and methylene blue reduction, respectively, are obtained. In addition, activity values for hydrogen production from borohydride are as high as 25.0 L H2 g−1 min−1, even at room temperature. These values outperform any current state-of-the-art proposed catalysis strategies for water remediation reactions by at least 10-times and are superior to most advanced approaches to generate hydrogen from borohydride. The recyclability of the nanowires together with the simplicity of the synthetic method makes this approach (using not only Co–Pt, but also other mesoporous magnetic catalysts) very appealing for very diverse types of catalytic applications. © 2017 Elsevier B.V.

View abstract
Maximizing Exchange Bias in Co/CoO Core/Shell Nanoparticles by Lattice Matching between the Shell and the Embedding Matrix
González J.A., Andrés J.P., López Antón R., De Toro J.A., Normile P.S., Muniz P., Riveiro J.M., Nogués J. Chemistry of Materials; 29 (12): 5200 - 5206. 2017. 10.1021/acs.chemmater.7b00868. IF: 9.466

The exchange bias properties of 5 nm Co/CoO ferromagnetic/antiferromagnetic core/shell nanoparticles, highly dispersed in a CuxO matrix, have been optimized by matching the lattice parameter of the matrix with that of the CoO shell. Exchange bias and coercivity fields as large as HE = 7780 Oe and HC = 6950 Oe are linked to the presence of a Cu2O matrix (0.3% lattice mismatch with respect to the shells). The small mismatch between Cu2O and CoO plays a dual role: it (i) structurally stabilizes the CoO and (ii) favors the existence of a large amount of uncompensated moments in the shell that enhance the exchange bias effects. The results indicate that lattice matching may be a very efficient way to improve the exchange bias properties of core/shell nanoparticles, paving the way to novel approaches to tune their magnetic properties. © 2017 American Chemical Society.

View abstract
Novel Ba-hexaferrite structural variations stabilized on the nanoscale as building blocks for epitaxial bi-magnetic hard/soft sandwiched maghemite/hexaferrite/maghemite nanoplatelets with out-of-plane easy axis and enhanced magnetization
Belec B., Dražić G., Gyergyek S., Podmiljšak B., Goršak T., Komelj M., Nogués J., Makovec D. Nanoscale; 9 (44): 17551 - 17560. 2017. 10.1039/c7nr05894b. IF: 7.367

Atomic-resolution scanning-transmission electron microscopy showed that barium hexaferrite (BHF) nanoplatelets display a distinct structure, which represents a novel structural variation of hexaferrites stabilized on the nanoscale. The structure can be presented in terms of two alternating structural blocks stacked across the nanoplatelet: a hexagonal (BaFe6O11)2- R block and a cubic (Fe6O8)2+ spinel S block. The structure of the BHF nanoplatelets comprises only two, or rarely three, R blocks and always terminates at the basal surfaces with the full S blocks. The structure of a vast majority of the nanoplatelets can be described with a SR∗S∗RS stacking order, corresponding to a BaFe15O23 composition. The nanoplatelets display a large, uniaxial magnetic anisotropy with the easy axis perpendicular to the platelet, which is a crucial property enabling different novel applications based on aligning the nanoplatelets with applied magnetic fields. However, the BHF nanoplatelets exhibit a modest saturation magnetization, MS, of just over 30 emu g-1. Given the cubic S block termination of the platelets, layers of maghemite, γ-Fe2O3, (M), with a cubic spinel structure, can be easily grown epitaxially on the surfaces of the platelets, forming a sandwiched M/BHF/M platelet structure. The exchange-coupled composite nanoplatelets exhibit a remarkably uniform structure, with an enhanced MS of more than 50 emu g-1 while essentially maintaining the out-of-plane easy axis. The enhanced MS could pave the way for their use in diverse platelet-based magnetic applications. © 2017 The Royal Society of Chemistry.

View abstract
Remanence plots as a probe of spin disorder in magnetic nanoparticles
De Toro J.A., Vasilakaki M., Lee S.S., Andersson M.S., Normile P.S., Yaacoub N., Murray P., Sánchez E.H., Muñiz P., Peddis D., Mathieu R., Liu K., Geshev J., Trohidou K.N., Nogués J. Chemistry of Materials; 29 (19): 8258 - 8268. 2017. 10.1021/acs.chemmater.7b02522. IF: 9.466

Remanence magnetization plots (e.g., Henkel or δM plots) have been extensively used as a straightforward way to determine the presence and intensity of dipolar and exchange interactions in assemblies of magnetic nanoparticles or single domain grains. Their evaluation is particularly important in functional materials whose performance is strongly affected by the intensity of interparticle interactions, such as patterned recording media and nanostructured permanent magnets, as well as in applications such as hyperthermia and magnetic resonance imaging. Here, we demonstrate that δM plots may be misleading when the nanoparticles do not have a homogeneous internal magnetic configuration. Substantial dips in the M plots of γ-Fe2O3 nanoparticles isolated by thick SiO2 shells indicate the presence of demagnetizing interactions, usually identified as dipolar interactions. Our results, however, demonstrate that it is the inhomogeneous spin structure of the nanoparticles, as most clearly evidenced by Mössbauer measurements, that has a pronounced effect on the δM plots, leading to features remarkably similar to those produced by dipolar interactions. X-ray diffraction results combined with magnetic characterization indicate that this inhomogeneity is due to the presence of surface structural (and spin) disorder. Monte Carlo simulations unambiguously corroborate the critical role of the internal magnetic structure in the δM plots. Our findings constitute a cautionary tale on the widespread use of remanence plots to assess interparticle interactions as well as offer new perspectives in the use of Henkel and δM plots to quantify the rather elusive inhomogeneous magnetization states in nanoparticles. © 2017 American Chemical Society.

View abstract
Seeded Growth Synthesis of Au-Fe3O4 Heterostructured Nanocrystals: Rational Design and Mechanistic Insights
Fantechi E., Roca A.G., Sepúlveda B., Torruella P., Estradé S., Peiró F., Coy E., Jurga S., Bastús N.G., Nogués J., Puntes V. Chemistry of Materials; 29 (9): 4022 - 4035. 2017. 10.1021/acs.chemmater.7b00608. IF: 9.466

Multifunctional hybrid nanoparticles comprising two or more entities with different functional properties are gaining ample significance in industry and research. Due to its combination of properties, a particularly appealing example is Au-Fe3O4 composite nanoparticles. Here we present an in-depth study of the synthesis of Au-Fe3O4 heterostructured nanocrystals (HNCs) by thermal decomposition of iron precursors in the presence of preformed 10 nm Au seeds. The role of diverse reaction parameters on the HNCs formation was investigated using two different precursors: iron pentacarbonyl (Fe(CO)5) and iron acetylacetonate (Fe(acac)3). The reaction conditions promoting the heterogeneous nucleation of Fe3O4 onto Au seeds were found to significantly differ depending on the precursor chosen, where Fe(acac)3 is considerably more sensitive to the variation of the parameters than Fe(CO)5 and more subject to homogeneous nucleation processes with the consequent formation of isolated iron oxide nanocrystals (NCs). The role of the surfactants was also crucial in the formation of well-defined and monodisperse HNCs by regulating the access to the Au surface. Similarly, the variations of the [Fe]/[Au] ratio, temperature, and employed solvent were found to act on the mean size and the morphology of the obtained products. Importantly, while the optical properties are rather sensitive to the final morphology, the magnetic ones are rather similar for the different types of obtained HNCs. The surface functionalization of dimer-like HNCs with silica allows their dispersion in aqueous media, opening the path to their use in biomedical applications. © 2017 American Chemical Society.

View abstract
Tri-segmented magnetic nanowires with antiparallel alignment: Suitable platforms for biomedical applications with minimized agglomeration?
Sort J., Zhang J., Agramunt S., Del-Valle N., Navau C., Estradé S., Peiró F., Pané S., Sánchez A., Pellicer E., Nogues J. 2017 IEEE International Magnetics Conference, INTERMAG 2017; (8007843) 2017. 10.1109/INTMAG.2017.8007843.

Materials structured in the form of one-dimensional nanoarchitectures, such as nanorods and nanowires (NWs), have found widespread applications in several technological areas, such as optoelectronics, magnetism, catalysis, piezo- and thermo-electricity, biosensing, or micro-/nanoelectromechanical systems (MEMS/NEMS), among others. © 2017 IEEE.

View abstract
Unveiling a New High-Temperature Ordered Magnetic Phase in ϵ-Fe2O3
García-Muñoz J.L., Romaguera A., Fauth F., Nogués J., Gich M. Chemistry of Materials; 29 (22): 9705 - 9713. 2017. 10.1021/acs.chemmater.7b03417. IF: 9.466

Iron oxides are among the most abundant materials on Earth, and yet there are some of their basic properties which are still not well-established. Here, we present temperature-dependent magnetic, X-ray, and neutron diffraction measurements refuting the current belief that the magnetic ordering temperature of ϵ-Fe2O3 is ∼500 K, i.e., well below that of other iron oxides such as hematite, magnetite, or maghemite. Upon heating from room temperature, the ϵ-Fe2O3 nanoparticles' saturation magnetization undergoes a monotonic decrease while the coercivity and remanence sharply drop, virtually vanishing around ∼500 K. However, above that temperature the hysteresis loops present a nonlinear response with finite coercivity, making evident signs of ferrimagnetic order up to temperatures as high as 850 K (TN1). The neutron diffraction study confirms the presence of ferrimagnetic order well above 500 K with Pna'21' magnetic symmetry, but only involving two of the four Fe3+ sublattices which are ordered below TN2 ≈ 480 K, and with a reduced net ferromagnetic component, that vanishes at above 850 K. The results unambiguously show the presence of a high-temperature magnetic phase in ϵ-Fe2O3 with a critical temperature of TN1 ∼ 850 K. Importantly, this temperature is similar to the Curie point in other iron oxides, indicating comparable magnetic coupling strengths. The presence of diverse magnetic phases is further supported by the nonmonotonic evolution of the thermal expansion. The existence of a high-temperature ferrimagnetic phase in ϵ-Fe2O3 may open the door to further expand the working range of this multifunctional iron oxide. © 2017 American Chemical Society.

View abstract
Voltage-Induced Coercivity Reduction in Nanoporous Alloy Films: A Boost toward Energy-Efficient Magnetic Actuation
Quintana A., Zhang J., Isarain-Chávez E., Menéndez E., Cuadrado R., Robles R., Baró M.D., Guerrero M., Pané S., Nelson B.J., Müller C.M., Ordejón P., Nogués J., Pellicer E., Sort J. Advanced Functional Materials; 27 (32, 1701904) 2017. 10.1002/adfm.201701904. IF: 12.124

Magnetic data storage and magnetically actuated devices are conventionally controlled by magnetic fields generated using electric currents. This involves significant power dissipation by Joule heating effect. To optimize energy efficiency, manipulation of magnetic information with lower magnetic fields (i.e., lower electric currents) is desirable. This can be accomplished by reducing the coercivity of the actuated material. Here, a drastic reduction of coercivity is observed at room temperature in thick (≈600 nm), nanoporous, electrodeposited Cu–Ni films by simply subjecting them to the action of an electric field. The effect is due to voltage-induced changes in the magnetic anisotropy. The large surface-area-to-volume ratio and the ultranarrow pore walls of the system allow the whole film, and not only the topmost surface, to effectively contribute to the observed magnetoelectric effect. This waives the stringent “ultrathin-film requirement” from previous studies, where small voltage-driven coercivity variations were reported. This observation expands the already wide range of applications of nanoporous materials (hitherto in areas like energy storage or catalysis) and it opens new paradigms in the fields of spintronics, computation, and magnetic actuation in general. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

View abstract

2016

3D Visualization of the Iron Oxidation State in FeO/Fe3O4 Core-Shell Nanocubes from Electron Energy Loss Tomography
Torruella P., Arenal R., De La Peña F., Saghi Z., Yedra L., Eljarrat A., López-Conesa L., Estrader M., López-Ortega A., Salazar-Alvarez G., Nogués J., Ducati C., Midgley P.A., Peiró F., Estradé S. Nano Letters; 16 (8): 5068 - 5073. 2016. 10.1021/acs.nanolett.6b01922. IF: 13.779

The physicochemical properties used in numerous advanced nanostructured devices are directly controlled by the oxidation states of their constituents. In this work we combine electron energy-loss spectroscopy, blind source separation, and computed tomography to reconstruct in three dimensions the distribution of Fe2+ and Fe3+ ions in a FeO/Fe3O4 core/shell cube-shaped nanoparticle with nanometric resolution. The results highlight the sharpness of the interface between both oxides and provide an average shell thickness, core volume, and average cube edge length measurements in agreement with the magnetic characterization of the sample. © 2016 American Chemical Society.

View abstract
Effective ionic-liquid microemulsion based electrodeposition of mesoporous Co-Pt films for methanol oxidation catalysis in alkaline media
Serrà A., Gómez E., Golosovsky I.V., Nogués J., Vallés E. Journal of Materials Chemistry A; 4 (20): 7805 - 7814. 2016. 10.1039/c6ta02035f. IF: 8.262

Pt-based direct methanol fuel cells are attracting increasing interest as environmentally friendly alternative energy sources. However, the high price of Pt and the difficulty to prepare favourable morphologies for catalysis (e.g., mesoporous materials) are hampering their development into feasible products. Here, we demonstrate a novel approach to efficiently grow mesoporous films of Pt-poor alloys (Co3Pt and CoPt3), based on electrodeposition in ionic liquid-in-water (IL/W) microemulsions. The high proportion of the electrolytic aqueous solution in the IL/W microemulsion favors a significant deposition rate, while the presence of IL drops induces the formation of highly mesoporous films. The mesoporous alloys, with pores in the 8-11 nm range, exhibit excellent durability in acidic and alkaline aggressive media, maintaining their peculiar morphology. The structures are very efficient for the catalysis of methanol electro-oxidation in alkaline media, with minimal poisoning of the catalysts. These results pave the way to develop simple, versatile environmentally friendly fuel cell catalysts to commercialize new viable ecological alternative energy sources. © 2016 The Royal Society of Chemistry.

View abstract
Electrochemically synthesized amorphous and crystalline nanowires: Dissimilar nanomechanical behavior in comparison with homologous flat films
Zeeshan M.A., Esqué-De Los Ojos D., Castro-Hartmann P., Guerrero M., Nogués J., Suriñach S., Baró M.D., Nelson B.J., Pané S., Pellicer E., Sort J. Nanoscale; 8 (3): 1344 - 1351. 2016. 10.1039/c5nr04398k. IF: 7.760

The effects of constrained sample dimensions on the mechanical behavior of crystalline materials have been extensively investigated. However, there is no clear understanding of these effects in nano-sized amorphous samples. Herein, nanoindentation together with finite element simulations are used to compare the properties of crystalline and glassy CoNi(Re)P electrodeposited nanowires (φ ≈ 100 nm) with films (3 μm thick) of analogous composition and structure. The results reveal that amorphous nanowires exhibit a larger hardness, lower Young's modulus and higher plasticity index than glassy films. Conversely, the very large hardness and higher Young's modulus of crystalline nanowires are accompanied by a decrease in plasticity with respect to the homologous crystalline films. Remarkably, proper interpretation of the mechanical properties of the nanowires requires taking the curved geometry of the indented surface and sink-in effects into account. These findings are of high relevance for optimizing the performance of new, mechanically-robust, nanoscale materials for increasingly complex miniaturized devices. © 2016 The Royal Society of Chemistry.

View abstract
Galvanic Replacement onto Complex Metal-Oxide Nanoparticles: Impact of Water or Other Oxidizers in the Formation of either Fully Dense Onion-like or Multicomponent Hollow MnOx/FeOx Structures
López-Ortega A., Roca A.G., Torruella P., Petrecca M., Estradé S., Peiró F., Puntes V., Nogués J. Chemistry of Materials; 28 (21): 8025 - 8031. 2016. 10.1021/acs.chemmater.6b03765. IF: 9.407

Multicomponent metal-oxide nanoparticles are appealing structures from applied and fundamental viewpoints. The control on the synthetic parameters in colloidal chemistry allows the growth of complex nanostructures with novel morphologies. In particular, the synthesis of biphase metal-oxide hollow nanoparticles has been reported based on galvanic replacement using an organic-based seeded-growth approach, but with the presence of H2O. Here we report a novel route to synthesize either fully dense or hollow core/shell metal-oxide nanoparticles (MnOx/FeOx) by simply adding or not oxidants in the reaction. We demonstrate that the presence of oxidants (e.g., O2 carried by the not properly degassed H2O or (CH3)3NO) allows the formation of hollow structures by a galvanic reaction between the MnOx and FeOx phases. In particular, the use of (CH3)3NO as oxidant allows for the first time a very reliable all-organic synthesis of hollow MnOx/FeOx nanoparticles without the need of water (with a somewhat unreliable oxidation role). Oxidants permit the formation of MnOx/FeOx hollow nanoparticles by an intermediate step where the MnO/Mn3O4 seeds are oxidized into Mn3O4, thus allowing the Mn3+ → Mn2+ reduction by the Fe2+ ions. The lack of proper oxidative conditions leads to full-dense onion-like core/shell MnO/Mn3O4/Fe3O4 particles. Thus, we show that the critical step for galvanic replacement is the proper seed oxidation states so that their chemical reduction by the shell ions is thermodynamically favored. © 2016 American Chemical Society.

View abstract
Highly efficient electrochemical and chemical hydrogenation of 4-nitrophenol using recyclable narrow mesoporous magnetic CoPt nanowires
Serrà A., Alcobé X., Sort J., Nogués J., Vallés E. Journal of Materials Chemistry A; 4 (40): 15676 - 15687. 2016. 10.1039/c6ta07149j. IF: 8.262

Toxic nitro-compounds, such as 4-nitrophenol, are one of the most common wastewater industrial pollutants. Thus, efficient ways to neutralize them are actively pursued. Here novel procedures to degrade these types of compounds based on the use of mesoporous magnetic nanowires are demonstrated. Fully-mesoporous magnetic narrow (25 nm) CoPt nanowires with an extraordinary effective area are grown using ionic liquid-in-water microemulsions in alumina templates. These mesoporous nanowires are shown to be efficient catalysts for the hydrogenation of 4-nitrophenol by electrocatalysis. Additionally, these nanowires also present exceptional conventional catalytic activity when used in conjunction with NaBH4, particularly when magnetic stirring is utilized. In fact, magnetically actuated mesoporous CoPt nanowires drastically outperform all state-of-the-art 4-nitrophenol catalysts. Additionally, given their magnetic character, these nanowires can be easily recycled and reused. Thus, the outstanding catalytic performance of mesoporous CoPt nanowires makes them excellent candidates for wastewater treatment agents. © 2016 The Royal Society of Chemistry.

View abstract
Modeling the collective magnetic behavior of highly-packed arrays of multi-segmented nanowires
Agramunt-Puig S., Del-Valle N., Pellicer E., Zhang J., Nogués J., Navau C., Sanchez A., Sort J. New Journal of Physics; 18 (1, 013026) 2016. 10.1088/1367-2630/18/1/013026. IF: 3.570

A powerful model to evaluate the collective magnetic response of large arrays of segmented nanowires comprising two magnetic segments of dissimilar coercivity separated by a non-magnetic spacer is introduced. The model captures the essential aspects of the underlying physics in these systems while being at the same time computationally tractable for relatively large arrays. The minimum lateral and vertical distances rendering densely packed weakly-interacting nanowires and segments are calculated for optimizing their performance in applications like magnetic sensors or recording media. The obtained results are appealing for the design of multifunctional miniaturized devices actuated by external magnetic fields, whose successful implementation relies on achieving a delicate balance between two opposing technological demands: the need for an ultra-high density of nanowires per unit area and the minimization of inter-wire and inter-segment dipolar interactions. © 2016 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

View abstract
Spontaneous formation of spiral-like patterns with distinct periodic physical properties by confined electrodeposition of Co-In disks
Golvano-Escobal I., Gonzalez-Rosillo J.C., Domingo N., Illa X., López-Barberá J.F., Fornell J., Solsona P., Aballe L., Foerster M., Surinãch S., Baró M.D., Puig T., Pané S., Nogués J., Pellicer E., Sort J. Scientific Reports; 6 ( 30398) 2016. 10.1038/srep30398. IF: 5.228

Spatio-temporal patterns are ubiquitous in different areas of materials science and biological systems. However, typically the motifs in these types of systems present a random distribution with many possible different structures. Herein, we demonstrate that controlled spatio-temporal patterns, with reproducible spiral-like shapes, can be obtained by electrodeposition of Co-In alloys inside a confined circular geometry (i.e., in disks that are commensurate with the typical size of the spatio-temporal features). These patterns are mainly of compositional nature, i.e., with virtually no topographic features. Interestingly, the local changes in composition lead to a periodic modulation of the physical (electric, magnetic and mechanical) properties. Namely, the Co-rich areas show higher saturation magnetization and electrical conductivity and are mechanically harder than the In-rich ones. Thus, this work reveals that confined electrodeposition of this binary system constitutes an effective procedure to attain template-free magnetic, electric and mechanical surface patterning with specific and reproducible shapes.

View abstract
Tailoring Staircase-like Hysteresis Loops in Electrodeposited Trisegmented Magnetic Nanowires: A Strategy toward Minimization of Interwire Interactions
Zhang J., Agramunt-Puig S., Del-Valle N., Navau C., Baró M.D., Estradé S., Peiró F., Pané S., Nelson B.J., Sanchez A., Nogués J., Pellicer E., Sort J. ACS Applied Materials and Interfaces; 8 (6): 4109 - 4117. 2016. 10.1021/acsami.5b11747. IF: 7.145

A new strategy to minimize magnetic interactions between nanowires (NWs) dispersed in a fluid is proposed. Such a strategy consists of preparing trisegmented NWs containing two antiparallel ferromagnetic segments with dissimilar coercivity separated by a nonmagnetic spacer. The trisegmented NWs exhibit a staircase-like hysteresis loop with tunable shape that depends on the relative length of the soft- and hard-magnetic segments and the respective values of saturation magnetization. Such NWs are prepared by electrodepositing CoPt/Cu/Ni in a polycarbonate (PC) membrane. The antiparallel alignment is set by applying suitable magnetic fields while the NWs are still embedded in the PC membrane. Analytic calculations are used to demonstrate that the interaction magnetic energy from fully compensated trisegmented NWs with antiparallel alignment is reduced compared to a single-component NW with the same length or the trisegmented NWs with the two ferromagnetic counterparts parallel to each other. The proposed approach is appealing for the use of magnetic NWs in certain biological or catalytic applications where the aggregation of NWs is detrimental for optimized performance. © 2016 American Chemical Society.

View abstract
Tunable High-Field Magnetization in Strongly Exchange-Coupled Freestanding Co/CoO Core/Shell Coaxial Nanowires
Salazar-Alvarez G., Geshev J., Agramunt-Puig S., Navau C., Sanchez A., Sort J., Nogués J. ACS Applied Materials and Interfaces; 8 (34): 22477 - 22483. 2016. 10.1021/acsami.6b05588. IF: 7.145

The exchange bias properties of Co/CoO coaxial core/shell nanowires were investigated with cooling and applied fields perpendicular to the wire axis. This configuration leads to unexpected exchange-bias effects. First, the magnetization value at high fields is found to depend on the field-cooling conditions. This effect arises from the competition between the magnetic anisotropy and the Zeeman energies for cooling fields perpendicular to the wire axis. This allows imprinting predefined magnetization states to the antiferromagnetic (AFM) shell, as corroborated by micromagnetic simulations. Second, the system exhibits a high-field magnetic irreversibility, leading to open hysteresis loops attributed to the AFM easy axis reorientation during the reversal (effect similar to athermal training). A distinct way to manipulate the high-field magnetization in exchange-biased systems, beyond the archetypical effects, was thus experimentally and theoretically demonstrated. © 2016 American Chemical Society.

View abstract

2015

A new reversal mode in exchange coupled antiariomagnetic/ferromagnetic disks: Distorted viscous vortex
Gilbert D.A., Ye L., Varea A., Agramunt-Puig S., Del Valle N., Navau C., Lopez-Barbera J.F., Buchanan K.S., Hoffmann A., Sanchez A., Sort J., Liu K., Nogues J. Nanoscale; 7 (21): 9878 - 9885. 2015. 10.1039/c5nr01856k. IF: 7.394

Magnetic vortices have generated intense interest in recent years due to their unique reversal mechanisms, fascinating topological properties, and exciting potential applications. In addition, the exchange coupling of magnetic vortices to antiferromagnets has also been shown to lead to a range of novel phenomena and functionalities. Here we report a new magnetization reversal mode of magnetic vortices in exchange coupled Ir20Mn80/Fe20Ni80 microdots: distorted viscous vortex reversal. In contrast to the previously known or proposed reversal modes, the vortex is distorted close to the interface and viscously dragged due to the uncompensated spins of a thin antiferromagnet, which leads to unexpected asymmetries in the annihilation and nucleation fields. These results provide a deeper understanding of the physics of exchange coupled vortices and may also have important implications for applications involving exchange coupled nanostructures. This journal is © The Royal Society of Chemistry.

View abstract
Applications of exchange coupled bi-magnetic hard/soft and soft/hard magnetic core/shell nanoparticles
López-Ortega A., Estrader M., Salazar-Alvarez G., Roca A.G., Nogués J. Physics Reports; 553: 1 - 32. 2015. 10.1016/j.physrep.2014.09.007. IF: 20.033

The applications of exchange coupled bi-magnetic hard/soft and soft/hard ferromagnetic core/shell nanoparticles are reviewed. After a brief description of the main synthesis approaches and the core/shell structural-morphological characterization, the basic static and dynamic magnetic properties are presented. Five different types of prospective applications, based on diverse patents and research articles, are described: permanent magnets, recording media, microwave absorption, biomedical applications and other applications. Both the advantages of the core/shell morphology and some of the remaining challenges are discussed. © 2014 Elsevier B.V.

View abstract
Enhanced magnetic properties in antiferromagnetic-core/ferrimagnetic-shell nanoparticles
Vasilakaki M., Trohidou K.N., Nogués J. Scientific Reports; 5 ( 9609) 2015. 10.1038/srep09609. IF: 5.578

Bi-magnetic core/shell nanoparticles are gaining increasing interest due to their foreseen applications. Inverse antiferromagnetic(AFM)/ferrimagnetic(FiM) core/shell nanoparticles are particularly appealing since they may overcome some of the limitations of conventional FiM/AFM systems. However, virtually no simulations exist on this type of morphology. Here we present systematic Metropolis Monte Carlo simulations of the exchange bias properties of such nanoparticles. The coercivity, H C, and loop shift, H ex, present a non-monotonic dependence with the core diameter and the shell thickness, in excellent agreement with the available experimental data. Additionally, we demonstrate novel unconventional behavior in FiM/AFM particles. Namely, while H C and H ex decrease upon increasing FiM thickness for small AFM cores (as expected), they show the opposite trend for large cores. This presents a counterintuitive FiM size dependence for large AFM cores that is attributed to the competition between core and shell contributions, which expands over a wider range of core diameters leading to non-vanishing H ex even for very large cores. Moreover, the results also hint different possible ways to enhance the experimental performance of inverse core/shell nanoparticles for diverse applications.

View abstract
High Temperature Magnetic Stabilization of Cobalt Nanoparticles by an Antiferromagnetic Proximity Effect
De Toro J.A., Marques D.P., Muñiz P., Skumryev V., Sort J., Givord D., Nogués J. Physical Review Letters; 115 (5, 057201) 2015. 10.1103/PhysRevLett.115.057201. IF: 7.512

Thermal activation tends to destroy the magnetic stability of small magnetic nanoparticles, with crucial implications for ultrahigh density recording among other applications. Here we demonstrate that low-blocking-temperature ferromagnetic (FM) Co nanoparticles (TB<70K) become magnetically stable above 400 K when embedded in a high-Néel-temperature antiferromagnetic (AFM) NiO matrix. The origin of this remarkable TB enhancement is due to a magnetic proximity effect between a thin CoO shell (with low Néel temperature, TN, and high anisotropy, KAFM) surrounding the Co nanoparticles and the NiO matrix (with high TN but low KAFM). This proximity effect yields an effective antiferromagnet with an apparent TN beyond that of bulk CoO, and an enhanced anisotropy compared to NiO. In turn, the Co core FM moment is stabilized against thermal fluctuations via core-shell exchange-bias coupling, leading to the observed TB increase. Mean-field calculations provide a semiquantitative understanding of this magnetic-proximity stabilization mechanism. © 2015 American Physical Society.

View abstract
Origin of the large dispersion of magnetic properties in nanostructured oxides: FexO/Fe3O4 nanoparticles as a case study
Estrader M., Lopez-Ortega A., Golosovsky I.V., Estrade S., Roca A.G., Salazar-Alvarez G., Lopez-Conesa L., Tobia D., Winkler E., Ardisson J.D., Macedo W.A.A., Morphis A., Vasilakaki M., Trohidou K.N., Gukasov A., Mirebeau I., Makarova O.L., Zysler R.D., Peiro F., Baro M.D., Bergstrom L., Nogues J. Nanoscale; 7 (7): 3002 - 3015. 2015. 10.1039/c4nr06351a. IF: 7.394

The intimate relationship between stoichiometry and physicochemical properties in transition-metal oxides makes them appealing as tunable materials. These features become exacerbated when dealing with nanostructures. However, due to the complexity of nanoscale materials, establishing a distinct relationship between structure-morphology and functionalities is often complicated. In this regard, in the FexO/Fe3O4 system a largely unexplained broad dispersion of magnetic properties has been observed. Here we show, thanks to a comprehensive multi-technique approach, a clear correlation between the magneto-structural properties in large (45 nm) and small (9 nm) FexO/Fe3O4 core/shell nanoparticles that can explain the spread of magnetic behaviors. The results reveal that while the FexO core in the large nanoparticles is antiferromagnetic and has bulk-like stoichiometry and unit-cell parameters, the FexO core in the small particles is highly non-stoichiometric and strained, displaying no significant antiferromagnetism. These results highlight the importance of ample characterization to fully understand the properties of nanostructured metal oxides. © 2015 The Royal Society of Chemistry.

View abstract

2014

A combinatorial study of the mechanical and magnetic properties of a gradually nitrided austenitic stainless steel single crystal
Menéndez, E.; Templier, C.; Abrasonis, G.; Lopez-Barbera, J.F.; Nogués, J.; Temst, K.; Sort, J. CrystEngComm; 16 (17): 3515 - 3520. 2014. 10.1039/c3ce42379d. IF: 3.858
Direct evidence for an interdiffused intermediate layer in bi-magnetic core-shell nanoparticles
Juhin A.; Lopez-Ortega A.; Sikora M.; Carvallo C.; Estrader M.; Estrade S.; Peiro F.; Baro M.D.; Sainctavit P.; Glatzel P.; Nogues J. Nanoscale; 6 (20): 11911 - 11920. 2014. . IF: 6.739
Green electrochemical template synthesis of CoPt nanoparticles with tunable size, composition, and magnetism from microemulsions using an ionic liquid (bmimPF6)
Serrà, A.; Gómez, E.; López-Barbera, J.F.; Nogués, J.; Vallés, E. ACS Nano; 8 (5): 4630 - 4639. 2014. 10.1021/nn500367q. IF: 12.033
Interdependence between training and magnetization reversal in granular Co-CoO exchange bias systems
Menendez E.; Dias T.; Geshev J.; Lopez-Barbera J.F.; Nogues J.; Steitz R.; Kirby B.J.; Borchers J.A.; Pereira L.M.C.; Vantomme A.; Temst K. Physical Review B - Condensed Matter and Materials Physics; 2014. 10.1103/PhysRevB.89.144407. IF: 3.664
One-pot electrosynthesis of multi-layered magnetic metallopolymer nanocomposites
Özkale, B.; Pellicer, E.; Zeeshan, M.A.; López-Barberá, J.F.; Nogués, J.; Sort, J.; Nelson, B.J.; Pané, S. Nanoscale; 6 (9): 4683 - 4690. 2014. 10.1039/c3nr06131k. IF: 6.739
Oxide wizard: An EELS application to characterize the white lines of transition metal edges
Yedra L.; Xuriguera E.; Estrader M.; Lopez-Ortega A.; Baro M.D.; Nogues J.; Roldan M.; Varela M.; Estrade S.; Peiro F. Microscopy and Microanalysis; 20 (3): 698 - 705. 2014. 10.1017/S1431927614000440. IF: 2.161

2013

Controlled 3D-coating of the pores of highly ordered mesoporous antiferromagnetic Co3O4 replicas with ferrimagnetic FexCo3-xO4 nanolayers
Pellicer, E.; Cabo, M.; López-Ortega, A.; Estrader, M.; Yedra, L.; Estradé, S.; Peiró, F.; Saghi, Z.; Midgley, P.; Rossinyol, E.; Golosovsky, I.V.; Mayoral, A.; Prades, J.D.; Suriñach, S.; Baró, M.D.; Sort, J.; Nogués, J. Nanoscale; 5: 5561 - 5567. 2013. 10.1039/c3nr00989k. IF: 6.233
Correlating material-specific layers and magnetic distributions within onion-like Fe3O4/MnO/¿¿Mn2O3 core/shell nanoparticles
Krycka, K. L.; Borchers, J. A.; Laver, M.; Salazar-Alvarez, G.; Lopez-Ortega, A.; Estrader, M.; Surinach, S.; Baro, M. D.; Sort, J.; Nogues, J. Journal of Applied Physics; 113 0 2013. 10.1063/1.4801423. IF: 2.210
Improving the magnetic properties of Co-CoO systems by designed oxygen implantation profiles
Menéndez, E.; Demeter, J.; Eyken, J.V.; Nawrocki, P.; Jedryka, E.; Wójcik, M.; Lopez-Barbera, J.F.; Nogués, J.; Vantomme, A.; Temst, K. ACS applied materials & interfaces; 5: 4320 - 4327. 2013. 10.1021/am400529r. IF: 5.008
Magnetic properties of single crystalline expanded austenite obtained by plasma nitriding of austenitic stainless steel single crystals
Menéndez, E.; Templier, C.; Garcia-Ramirez, P.; Santiso, J.; Vantomme, A.; Temst, K.; Nogués, J. ACS applied materials & interfaces; 5: 10118 - 10126. 2013. 10.1021/am402773w. IF: 5.008
Mesoporous oxide-diluted magnetic semiconductors prepared by co implantation in nanocast 3D-ordered In2O3-y materials
Pellicer, E.; Menéndez, E.; Fornell, J.; Nogués, J.; Vantomme, A.; Temst, K.; Sort, J. Journal of Physical Chemistry C; 117 (33): 17084 - 17091-17091. 2013. 10.1021/jp405376k. IF: 4.814
Optimizing the Refractive Index Sensitivity of Plasmonically Coupled Gold Nanoparticles
Varea, A.; Pané, S.; Gerstl, S.; Zeeshan, M.A.; Özkale, B.; Nelson, B.J.; Suriñach, S.; Baró, M.D.; Nogués, J.; Sort, J.; Pellicer, E. Plasmonics; 1: 1 - 8. 2013. 10.1007/s11468-013-9659-y. IF: 2.425
Ordered arrays of ferromagnetic, compositionally graded Cu 1-xNix alloy nanopillars prepared by template-assisted electrodeposition
Varea, A.; Pané, S.; Gerstl, S.; Zeeshan, M.A.; Özkale, B.; Nelson, B.J.; Suriñach, S.; Baró, M.D.; Nogués, J.; Sort, J.; Pellicer, E. Journal of Materials Chemistry C; 1 (43): 7215 - 7221. 2013. 10.1039/c3tc31310g. IF: 6.108
Polarizability and magnetoplasmonic properties of magnetic general nanoellipsoids
Maccaferri, N.; González-Diaz, J.B.; Bonetti, S.; Berger, A.; Kataja, M.; Van Dijken, S.; Nogués, J.; Bonanni, V.; Pirzadeh, Z.; Dmitriev, A.; Åkerman, J.; Vavassori, P. Optics Express; 21 (8): 9875 - 9889-9889. 2013. 10.1364/OE.21.009875. IF: 3.546
Resolving material-specific structures within Fe3O 4|γ-Mn2O3 core|shell nanoparticles using anomalous small-angle X-ray scattering
Krycka, K.L.; Borchers, J.A.; Salazar-Alvarez, G.; López-Ortega, A.; Estrader, M.; Estradé, S.; Winkler, E.; Zysler, R.D.; Sort, J.; Peiró, F.; Baró, M.D.; Kao, C.-C.; Nogués, J. ACS Nano; 7: 921 - 931. 2013. 10.1021/nn303600e. IF: 12.062
Robust antiferromagnetic coupling in hard-soft bi-magnetic core/shell nanoparticles
Estrader, M.; López-Ortega, A.; Estradé, S.; Golosovsky, I.V.; Salazar-Alvarez, G.; Vasilakaki, M.; Trohidou, K.N.; Varela, M.; Stanley, D.C.; Sinko, M.; Pechan, M.J.; Keavney, D.J.; Peiró, F.; Suriñach, S.; Baró, M.D.; Nogués, J. Nature Communications; 4 2013. 10.1038/ncomms3960. IF: 10.015
Tuning the magneto-optical response of nanosize ferromagnetic Ni disks using the phase of localized plasmons
Maccaferri, N.; Berger, A.; Bonetti, S.; Bonanni, V.; Kataja, M.; Qin, Q.H.; Van Dijken, S.; Pirzadeh, Z.; Dmitriev, A.; Nogués, J.; Åkerman, J.; Vavassori, P. Physical Review Letters; 2013. 10.1103/PhysRevLett.111.167401. IF: 7.943

2012

Cuando el desorden genera magnetismo
Menéndez, E. ; Sort, J. ; Varea, A. ; Concustell, A. ; Suriñach, S. ; Montserrat, J. ; Lora-Tamayo, E. ; Baró, M. D.; Nogués, J. Revista Española de Física; 26-gen.: 31 - 37. 2012. .
Distinguishing the core from the shell in MnO x/MnO y and FeO x/MnO x core/shell nanoparticles through quantitative electron energy loss spectroscopy (EELS) analysis
Estradé, S.; Yedra, L.; López-Ortega, A.; Estrader, M.; Salazar-Alvarez, G.; Baró, M.D.; Nogués, J.; Peiró, F. Micron; 43: 30 - 36. 2012. 10.1016/j.micron.2011.04.002.
Mesoscopic model for the simulation of large arrays of bi-magnetic core/shell nanoparticles
Margaris, G. ; Trohidou, K. N. ; Nogués, J. Advanced Materials; 24: 4331 - 4336. 2012. DOI: 10.1002/adma.201200615.
Strongly exchange coupled inverse ferrimagnetic soft/hard, Mn xFe 3-xO 4/Fe xMn 3-xO 4, core/shell heterostructured nanoparticles
López-Ortega, A.; Estrader, M.; Salazar-Alvarez, G.; Estradé, S.; Golosovsky, I.V.; Dumas, R.K.; Keavney, D.J.; Vasilakaki, M.; Trohidou, K.N.; Sort, J.; Peiró, F.; Suriñach, S.; Baró, M.D.; Nogués, J. Nanoscale; 4: 5138 - 5147. 2012. 10.1039/c2nr30986f.

2011

Designer magnetoplasmonics with nickel nanoferromagnets
Bonanni, V.; Bonetti, S.; Pakizeh, T.; Pirzadeh, Z.; Chen, J.; Nogués, J.; Vavassori, P.; Hillenbrand, R.; Åkerman, J.; Dmitriev, A. Nano Letters; 11: 5333 - 5338. 2011. 10.1021/nl2028443.
Graded Anisotropy FePtCu Films
Dumas, R.K.; Chaolin Zha; Yeyu Fang; Bonanni, V.; Lau, J.W.; Nogues, J.; Akerman, J. IEEE Transactions on Magnetics; 2011. .
Grain boundary segregation and interdiffusion effects in nickel-copper alloys: An effective means to improve the thermal stability of nanocrystalline nickel
Pellicer, E.; Varea, A.; Sivaraman, K.M.; Pané, S.; Surinach, S.; Baró, M.D.; Nogués, J.; Nelson, B.J.; Sort, J. ACS applied materials & interfaces; 3: 2265 - 2274. 2011. 10.1021/am2004587.
Nanostructured MnGa films on Si/SiO2 with 20.5 kOe room temperature coercivity
Zha, C.L.; Dumas, R.K.; Lau, J.W.; Mohseni, S.M.; Sani, S.R.; Golosovsky, I.V.; Monsen, Á.F.; Nogués, J.; Åkerman, J. Journal of Applied Physics; 110 2011. 10.1063/1.3656457.
Plasmonic nickel nanoantennas
Chen, J.; Albella, P.; Pirzadeh, Z.; Alonso-González, P.; Huth, F.; Bonetti, S.; Bonanni, V.; Åkerman, J.; Nogués, J.; Vavassori, P.; Dmitriev, A.; Aizpurua, J.; Hillenbrand, R. Small; 7: 2341 - 2347. 2011. 10.1002/smll.201100640.
Probing vertically graded anisotropy in FePtCu films
Dumas, R.K.; Fang, Y; Kirby, B.J.; Zha, C.; Bonanni, V.; Nogués, J.; Åkerman, J. Physical Review B; 2011. .
Role of anisotropy configuration in exchange-biased systems.
Jiménez, E.; Camarero, J.; Perna, P. ; Mikuszeit, N. ; Teran, F. J.; Sort, J. ; Nogués, J. ; García-Martín, J. M.; Hoffmann, A.; Dieny, B.; Miranda, R. Journal of Applied Physics; 109 (7): 07D730. 2011. 10.1063/1.3562507.
Role of the oxygen partial pressure in the formation of composite Co-CoO nanoparticles by reactive aggregation
De Toro, J.A.; Andrés, J.P.; González, J.A.; Riveiro, J.M.; Estrader, M.; López-Ortega, A.; Tsiaoussis, I.; Frangis, N.; Nogués, J. Journal of Nanoparticle Research; 13: 4583 - 4590. 2011. 10.1007/s11051-011-0418-8.
Tuneable magnetic patterning of paramagnetic Fe60Al40 (at.%) by consecutive ion irradiation through pre-lithographed shadow masks
Varea, A.; Menéndez, E.; Montserrat, J.; Lora-Tamayo, E.; Weber, A.; Heyderman, L.J.; Deevi, S.C.; Rao, K.V.; Suriñach, S.; Baró, M.D.; Buchanan, K.S.; Nogués, J.; Sort, J. Journal of Applied Physics; 109 2011. 10.1063/1.3590158.
Two-, Three-, and four-component magnetic multilayer onion nanoparticles based on iron oxides and manganese oxides
Salazar-Alvarez, G.; Lidbaum, H.; López-Ortega, A.; Estrader, M.; Leifer, K.; Sort, J.; Suriñach, S.; Baró, M.D.; Nogués, J. Journal of the American Chemical Society; 133: 16738 - 16741. 2011. 10.1021/ja205810t.

2010

983-991 Nanocrystalline electroplated Cu-Ni: Metallic thin films with enhanced mechanical properties and tunable magnetic behavior
Pellicer, E.; Varea, A.; Pané, S.; Nelson, B.J.; Menéndez, E.; Estrader, M.; Suriñach, S.; Baró, M.D.; Nogués, J.; Sort, J. Advanced Functional Materials; 20: 983 - 991. 2010. 10.1002/adfm.200901732.
Continuously graded anisotropy in single (Fe53 Pt 47)100-x Cux films
Zha, C.L.; Dumas, R.K.; Fang, Y.Y.; Bonanni, V.; Nogués, J.; Åkerman, J. Applied Physics Letters; 97 2010. 10.1063/1.3505521.
Exchange bias like effect in L10 (111) FePt-Based Pseudo Spin Valves
Zha, C.L.; Muduli, P.; Nogues, J.; Åkerman, J. Journal of Physics: Conference Series; 2010. .
First-order reversal curve analysis of graded anisotropy FePtCu films
Bonanni, V.; Fang, Y.; Dumas, R.K.; Zha, C.; Bonetti, S.; Nogués, J.; Åkerman, J. Applied Physics Letters; 97 2010. 10.1063/1.3515907.
Magnetic measurements as a sensitive tool for studying dehydrogenation processes in hydrogen storage materials
Menéndez, E.; Garroni, S.; López-Ortega, A.; Estrader, M.; Liedke, M.O.; Fassbender, J.; Solsona, P.; Suriñach, S.; Baró, M.D.; Nogués, J. Journal of Physical Chemistry C; 114: 16818 - 16822. 2010. 10.1021/jp105631z.
Making flexible magnetic aerogels and stiff magnetic nanopaper using cellulose nanofibrils as templates
Olsson, R.T.; Azizi Samir, M.A.S.; Salazar-Alvarez, G.; Belova, L.; Ström, V.; Berglund, L.A.; Ikkala, O.; Nogués, J.; Gedde, U.W. Nature Nanotechnology; 5: 584 - 588. 2010. 10.1038/nnano.2010.155.
Out-of-plane magnetic patterning based on indentation-induced nanocrystallization of a metallic glass
Sort, J.; Bonavina, L.F.; Varea, A.; Souza, C.; Botta, W.J.; Kiminami, C.S.; Bolfarini, C.; Suriñach, S.; Baró, M.D.; Nogués, J. Small; 6: 1543 - 1549. 2010. 10.1002/smll.201000510.
Pseudo spin valves using a (112)-textured D022 2.3-2.4Ga fixed layer
Zha, C.L.; Dumas, R.K.; Persson, J.; Mohseni, S.M.; Nogues, J.; Akerman, J. IEEE Magnetics Letters; 1 2010. 10.1109/LMAG.2009.2039774.
Size-dependent magnetic behavior and spin-wave gap in MnF2 epitaxial films with orthorhombic crystal structure
Golosovsky, I.V.; Sokolov, N.S.; Gukasov, A.; Bataille, A.; Boehm, M.; Nogués, J. Journal of Magnetism and Magnetic Materials; 322: 664 - 667. 2010. 10.1016/j.jmmm.2009.10.036.
Size-dependent passivation shell and magnetic properties in antiferromagnetic/ferrimagnetic core/shell MnO nanoparticles
Lopez-Ortega, A.; Tobia, D.; Winkler, E.; Golosovsky, I.V.; Salazar-Alvarez, G.; Estrade, S.; Estrader, M.; Sort, J.; González, M.A.; Suriñach, S.; Arbiol, J.; Peiró, F.; Zysler, R.D.; Baro, M.D.; Nogués, J. Journal of the American Chemical Society; 132: 9398 - 9407. 2010. 10.1021/ja1021798.
Synthesis of compositionally graded nanocast NiO/NiCo2O 4/Co3O4 mesoporous composites with tunable magnetic properties
Cabo, M.; Pellicer, E.; Rossinyol, E.; Estrader, M.; López-Ortega, A.; Nogués, J.; Castell, O.; Suriñach, S.; Baró, M.D. Journal of Materials Chemistry; 20: 7021 - 7028. 2010. 10.1039/c0jm00406e.

2009

Assessment of catalyst particle removal in multi-wall carbon nanotubes by highly sensitive magnetic measurements
Pellicer, E.; González-Guerrero, A.B.; Nogués, J.; Lechuga, L.M.; Mendoza, E. Carbon; 47: 758 - 763. 2009. 10.1016/j.carbon.2008.11.007.
Controlled generation of ferromagnetic martensite from paramagnetic austenite in AISI 316L austenitic stainless steel
Menéndez, E.; Sort, J .; Liedke, M.O.; Fassbender, J .; Suriñach, S.; Baró, M.D. ; Nogués, J. Journal of Materials Research; 24: 565 - 573. 2009. .
Direct evidence of imprinted vortex states in the antiferromagnet of exchange biased microdisks
Salazar-Alvarez, G.; Kavich, J.J.; Sort, J.; Mugarza, A.; Stepanow, S.; Potenza, A.; Marchetto, H.; Dhesi, S.S.; Baltz, V.; Dieny, B.; Weber, A.; Heyderman, L.J.; Nogués, J.; Gambardella, P. Applied Physics Letters; 95 2009. 10.1063/1.3168515.
Direct magnetic patterning due to the generation of ferromagnetism by selective ion irradiation of paramagnetic FeAl alloys
Menéndez, E.; Sort, J.; Liedke, M.O. ; Fassbender, J. ; Gemming, T.; Weber, A .; Heyderman, L.J.; Rao, K.V.; Deevi, S.C. ; Suriñach, S. ; Baró, M.D.; Nogués, J. Small; 5: 229 - 234. 2009. .
Emergence of noncollinear anisotropies from interfacial magnetic frustration in exchange-bias systems
Jiménez, E.; Camarero, J.; Sort, J.; Nogués, J.; Mikuszeit, N.; García-Martín, J.M.; Hoffmann, A.; Dieny, B.; Miranda, R. Physical Review B - Condensed Matter and Materials Physics; 80 2009. 10.1103/PhysRevB.80.014415.
Exchange bias in L10 (111)-oriented FePt-based pseudo spin valves
Zha, C.L.; Nogués, J.; Akerman, J. IEEE Transactions on Magnetics; 45: 3881 - 3884. 2009. .
Magnetic proximity effect features in antiferromagnetic/ferrimagnetic core-shell nanoparticles
Golosovsky, I.V.; Salazar-Alvarez, G.; López-Ortega, A.; González, M.A.; Sort, J.; Estrader, M.; Suriñach, S.; Baró, M.D.; Nogués, J. Physical Review Letters; 102 2009. 10.1103/PhysRevLett.102.247201.
Magnetization reversal in circularly exchange-biased ferromagnetic disks
Tanase, M.; Petford-Long, A.K.; Heinonen, O.; Buchanan, K.S.; Sort, J.; Nogués, J. Physical Review B - Condensed Matter and Materials Physics; 79 2009. 10.1103/PhysRevB.79.014436.
Nonzero orbital moment in high coercivity ε-Fe2O 3 and low-temperature collapse of the magnetocrystalline anisotropy
Tseng, Y.-C.; Souza-Neto, N.M.; Haskel, D.; Gich, M.; Frontera, C.; Roig, A.; Van Veenendaal, M.; Nogués, J. Physical Review B - Condensed Matter and Materials Physics; 79 2009. 10.1103/PhysRevB.79.094404.

2008

Cubic versus Spherical Magnetic Nanoparticles: The Role of Surface Anisotropy
G. Salazar-Alvarez; J. Qin; V. Sepelak; I. Bergmann; M. Vasilakaki; K. N. Trohidou; J. D. Ardisson; W. A. A. Macedo; M. Mikhaylova; M. Muhammed; M. D. Baro; J. Nogués Journal of the American Chemical Society; 130 (40): 13234 - 13239. 2008. 10.1021/ja0768744.
Direct measurement of depth-dependent Fe spin structure during magnetization reversal
W.A.A. Macedo; B. Sahoo; J. Eisenmenger; M.D. Martins; W. Keune; V. Kuncser; R. Röhlsberger; O. Leupold; R. Rüffer; J. Nogués; K. Liu; K. Schlage; I. K. Schuller Physical Review B; 78: 224401. 2008. 10.1103/PhysRevB.78.224401.
Enhanced exchange bias effects in a nanopatterned system consiting of two perpendicularly coupled ferromagnets
A. Bollero; B. Dieny; J. Sort; K.S. Buchanan; S. Landis; J. Nogués Applied Physics Letters; 92 (2): 22508. 2008. 10.1063/1.2833124 .
Exchange biased magnetic vortices
A. Hoffmann; J. Sort; K.S. Buchanan; J. Nogués IEEE Transactions on Magnetics; 44: 1968 - 1973. 2008. 10.1109/TMAG.2008.924547.
Ion mass dependence of irradiation-induced local creation of magnetism in Fe60Al40 alloys
J. Fassbender; M.O. Leidke; T. Strache; W. Möller; E. MEnéndez; J. Sort; K.V. Rao; S.C. Deevi; J. Nogués Physical Review B - Condensed Matter and Materials Physics; 77: 174430. 2008. 10.1103/PhysRevB.77.174430.
Magnetic properties of Ni-NiO (ferromagnetic-antiferromagnetic) nanocomposites obtained from partial mechanochemical reduction of NiO
J. Nogués; V. Langlais; J. Sort; S. Doppiu; S. Suriñach; M.D. Baró Journal of Nanoscience and Nanotechnology; 8: 2923 - 2928. 2008. 10.1166/jnn.2008.010.
Patterning of magnetic structures on austenitic stainless steel by local ion beam nitriding
E. Menendez; A. Martinavicius; M.O. Liedke; G. Abrasonis; J. Fassbender; J. Sommerlatte; K. Nielsch; S. Suriñach; M.D. Baro; J. Nogués; J. Sort Acta Materialia; 56: 4570. 2008. 10.1016/j.actamat.2008.05.014.
Tailoring the magnetization reversal of elliptical dots using exchange bias
J. Sort; K.S. Buchanan; J.E. Pearson; A. Hoffmann; E. Menendez; G. Salazar-Alvarez; M.D. Baró; M. Miron; B. Rodmacq; B. Dieny; J. Nogués Journal of Applied Physics; 103: 109. 2008. 10.1063/1.2840467.
Two-fold origin of the deformation-induced ferromagnetism in bulk Fe60Al40 (at%) alloys
E. Menéndez; J. Sort; M.O. Leidke; J. Fassbender; S. Surinach; M.D. Baró; J. Nogués New Journal of Physics; 19: 103030. 2008. 10.1088/1367-2630/10/10/103030.

2007

Cold compaction of metal¿ceramic (ferromagnetic¿antiferromagnetic) composites using high pressure torsion
E. Menéndez; J. Sort; V. Langlais; A. Zhilyaev; J. S. Muñoz; S. Suriñach; J. Nogués; M.D. Baró Journal of Alloys and Compounds; 434: 505 - 508. 2007. .
Enhanced coercivity in Co-rich non-stoichiometric CoxFe3-xO4+¿ nanoparticles prepared in large batches
G. Salazar-Alvarez; R.T. Olsson; J. Sort; W.A.A. Macedo; J.D. Ardison; M.D. Baró; U.W. Gedde; J. Nogués Chemistry of Materials; 2007. 10.1021/cm070827t.
Magnetic Instability Regions in Patterned Structures: Influence of Element Shape on Magnetization Reversal Dynamics
X. F. Han; M. Grimsditch; J. Meersschaut; A. Hoffmann; Y. Ji; J. Sort; J. Nogués; R. Divan; J. E. Pearson; D. J. Keavney Physical Review Letters; 2007. .
Microstructural evolution during solid state sintering of ball-milled nanocomposite WC-10 mass% Co powders
E Menéndez; J Sort; A Concustell; S Suriñach; J Nogués; M.D. Baró Nanotechnology; 2007. .
Reversible post-synthesis tuning of the superparamagnetic blocking temperature of ¿-Fe2O3 nanoparticles by adsorption and desorption of Co(II) ions
German Salazar-Alvarez; Jordi Sort; Abdusalam Uheida; Mamoun Muhammed; Santiago Suriñach; Maria Dolors Baró; Josep Nogués Journal of Medicinal Chemistry; 2007. .
Strong temperature dependence of antiferromagnetic coupling in CoFeB/Ru/CoFeB
N. Wiese; T. Dimopoulos; M. Rührig; J. Wecker; G. Reiss; J. Sort; J. Nogués Europhysics Letters; 78: 67002. 2007. doi:10.1209/0295-5075/78/67002.
Synthesis and size-dependent exchange bias in inverted core-shell MnO-Mn3O4 nanoparticles
G. Salazar-Alvarez; J. Sort; S. Suriñach; M.D. Baró; J. Nogués Journal of the American Chemical Society; 129: 9102 - 9108. 2007. 10.1021/ja0714282.
Tailoring deformation-induced effects in Co powders by milling them with ¿-Al2O3
E. Menéndez; J. Sort; S. Suriñach; M.D. Baró; J. Nogués Journal of Materials Research; 22: 2998 - 3005. 2007. .