Staff directory Jordi Sort Viñas

Jordi Sort Viñas

Visiting Researcher
Universitat Autònoma de Barcelona (UAB)
Magnetic Nanostructures



  • Dynamic electric-field-induced magnetic effects in cobalt oxide thin films: Towards magneto-ionic synapses

    Martins S., De Rojas J., Tan Z., Cialone M., Lopeandia A., Herrero-Martin J., Costa-Kramer J.L., Menendez E., Sort J. Nanoscale; 14 (3): 842 - 852. 2022. 10.1039/d1nr06210g. IF: 7.790

    Voltage control of magnetism via electric-field-driven ion migration (magneto-ionics) has generated intense interest due to its potential to greatly reduce heat dissipation in a wide range of information technology devices, such as magnetic memories, spintronic systems or artificial neural networks. Among other effects, oxygen ion migration in transition-metal-oxide thin films can lead to the generation or full suppression of controlled amounts of ferromagnetism ('ON-OFF' magnetic transitions) in a non-volatile and fully reversible manner. However, oxygen magneto-ionic rates at room temperature are generally considered too slow for industrial applications. Here, we demonstrate that sub-second ON-OFF transitions in electrolyte-gated paramagnetic cobalt oxide films can be achieved by drastically reducing the film thickness from >200 nm down to 5 nm. Remarkably, cumulative magneto-ionic effects can be generated by applying voltage pulses at frequencies as high as 100 Hz. Neuromorphic-like dynamic effects occur at these frequencies, including potentiation (cumulative magnetization increase), depression (i.e., partial recovery of magnetization with time), threshold activation, and spike time-dependent magnetic plasticity (learning and forgetting capabilities), mimicking many of the biological synapse functions. The systems under investigation show features that could be useful for the design of artificial neural networks whose magnetic properties would be governed with voltage. This journal is © The Royal Society of Chemistry.

  • Full-bandwidth electrophysiology of seizures and epileptiform activity enabled by flexible graphene microtransistor depth neural probes

    Bonaccini Calia A., Masvidal-Codina E., Smith T.M., Schäfer N., Rathore D., Rodríguez-Lucas E., Illa X., De la Cruz J.M., Del Corro E., Prats-Alfonso E., Viana D., Bousquet J., Hébert C., Martínez-Aguilar J., Sperling J.R., Drummond M., Halder A., Dodd A., Barr K., Savage S., Fornell J., Sort J., Guger C., Villa R., Kostarelos K., Wykes R.C., Guimerà-Brunet A., Garrido J.A. Nature Nanotechnology; 17 (3): 301 - 309. 2022. 10.1038/s41565-021-01041-9. IF: 39.213

    Mapping the entire frequency bandwidth of brain electrophysiological signals is of paramount importance for understanding physiological and pathological states. The ability to record simultaneously DC-shifts, infraslow oscillations (<0.1 Hz), typical local field potentials (0.1–80 Hz) and higher frequencies (80–600 Hz) using the same recording site would particularly benefit preclinical epilepsy research and could provide clinical biomarkers for improved seizure onset zone delineation. However, commonly used metal microelectrode technology suffers from instabilities that hamper the high fidelity of DC-coupled recordings, which are needed to access signals of very low frequency. In this study we used flexible graphene depth neural probes (gDNPs), consisting of a linear array of graphene microtransistors, to concurrently record DC-shifts and high-frequency neuronal activity in awake rodents. We show here that gDNPs can reliably record and map with high spatial resolution seizures, pre-ictal DC-shifts and seizure-associated spreading depolarizations together with higher frequencies through the cortical laminae to the hippocampus in a mouse model of chemically induced seizures. Moreover, we demonstrate the functionality of chronically implanted devices over 10 weeks by recording with high fidelity spontaneous spike-wave discharges and associated infraslow oscillations in a rat model of absence epilepsy. Altogether, our work highlights the suitability of this technology for in vivo electrophysiology research, and in particular epilepsy research, by allowing stable and chronic DC-coupled recordings. © 2021, The Author(s), under exclusive licence to Springer Nature Limited.

  • Voltage control of magnetism with magneto-ionic approaches: Beyond voltage-driven oxygen ion migration

    De Rojas J., Quintana A., Rius G., Stefani C., Domingo N., Costa-Krämer J.L., Menéndez E., Sort J. Applied Physics Letters; 120 (7, 070501) 2022. 10.1063/5.0079762. IF: 3.791

    Magneto-ionics is an emerging field in materials science where voltage is used as an energy-efficient means to tune magnetic properties, such as magnetization, coercive field, or exchange bias, by voltage-driven ion transport. We first discuss the emergence of magneto-ionics in the last decade, its core aspects, and key avenues of research. We also highlight recent progress in materials and approaches made during the past few years. We then focus on the "structural-ion"approach as developed in our research group in which the mobile ions are already present in the target material and discuss its potential advantages and challenges. Particular emphasis is given to the energetic and structural benefits of using nitrogen as the mobile ion, as well as on the unique manner in which ionic motion occurs in CoN and FeN systems. Extensions into patterned systems and textures to generate imprinted magnetic structures are also presented. Finally, we comment on the prospects and future directions of magneto-ionics and its potential for practical realizations in emerging fields, such as neuromorphic computing, magnetic random-access memory, or micro- and nano-electromechanical systems. © 2022 Author(s).


  • Critical Role of Electrical Resistivity in Magnetoionics

    De Rojas J., Salguero J., Quintana A., Lopeandia A., Liedke M.O., Butterling M., Attallah A.G., Hirschman E., Wagner A., Abad L., Costa-Krämer J.L., Sort J., Menéndez E. Physical Review Applied; 16 (3, 034042) 2021. 10.1103/PhysRevApplied.16.034042. IF: 4.985

    The utility of electrical resistivity as an indicator of magnetoionic performance in stoichiometrically and structurally similar thin-film systems is demonstrated. A series of highly nanocrystalline cobalt nitride (Co-N) thin films (85 nm thick) with a broad range of electrical properties exhibit markedly different magnetoionic behaviors. Semiconducting, near stoichiometric CoN films show the best performance, better than their metallic and insulating counterparts. Resistivity reflects the interplay between atomic bonding, carrier localization, and structural defects, and in turn determines the strength and distribution of applied electric fields inside the actuated films. This fact, generally overlooked, reveals that resistivity can be used to quickly evaluate the potential of a system to exhibit optimal magnetoionic effects, while also opening interesting challenges. © 2021 American Physical Society.

  • Magneto-Ionics in Single-Layer Transition Metal Nitrides

    De Rojas J., Salguero J., Ibrahim F., Chshiev M., Quintana A., Lopeandia A., Liedke M.O., Butterling M., Hirschmann E., Wagner A., Abad L., Costa-Krämer J.L., Menéndez E., Sort J. ACS Applied Materials and Interfaces; 13 (26): 30826 - 30834. 2021. 10.1021/acsami.1c06138. IF: 9.229

    Magneto-ionics allows for tunable control of magnetism by voltage-driven transport of ions, traditionally oxygen or lithium and, more recently, hydrogen, fluorine, or nitrogen. Here, magneto-ionic effects in single-layer iron nitride films are demonstrated, and their performance is evaluated at room temperature and compared with previously studied cobalt nitrides. Iron nitrides require increased activation energy and, under high bias, exhibit more modest rates of magneto-ionic motion than cobalt nitrides. Ab initio calculations reveal that, based on the atomic bonding strength, the critical field required to induce nitrogen-ion motion is higher in iron nitrides (≈6.6 V nm-1) than in cobalt nitrides (≈5.3 V nm-1). Nonetheless, under large bias (i.e., well above the magneto-ionic onset and, thus, when magneto-ionics is fully activated), iron nitride films exhibit enhanced coercivity and larger generated saturation magnetization, surpassing many of the features of cobalt nitrides. The microstructural effects responsible for these enhanced magneto-ionic effects are discussed. These results open up the potential integration of magneto-ionics in existing nitride semiconductor materials in view of advanced memory system architectures. © 2021 American Chemical Society. All rights reserved.


  • 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.

  • 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).


  • Disentangling Highly Asymmetric Magnetoelectric Effects in Engineered Multiferroic Heterostructures

    Menéndez E., Sireus V., Quintana A., Fina I., Casals B., Cichelero R., Kataja M., Stengel M., Herranz G., Catalán G., Baró M.D., Suriñach S., Sort J. Physical Review Applied; 12 (1, 014041) 2019. 10.1103/PhysRevApplied.12.014041. IF: 4.532

    One of the main strategies to control magnetism by voltage is the use of magnetostrictive-piezoelectric hybrid materials, such as ferromagnetic-ferroelectric heterostructures. When such heterostructures are subjected to an electric field, piezostrain-mediated effects, electronic charging, and voltage-driven oxygen migration (magnetoionics) may simultaneously occur, making the interpretation of the magnetoelectric effects not straightforward and often leading to misconceptions. Typically, the strain-mediated magnetoelectric response is symmetric with respect to the sign of the applied voltage because the induced strain (and variations in the magnetization) depends on the square of the ferroelectric polarization. Conversely, asymmetric responses can be obtained from electronic charging and voltage-driven oxygen migration. By engineering a ferromagnetic-ferroelectric hybrid consisting of a magnetically soft 50-nm thick Fe75Al25 (at. %) thin film on top of a (110)-oriented Pb(Mg1/3Nb2/3)O3-32PbTiO3 ferroelectric crystal, a highly asymmetric magnetoelectric response is obtained and the aforementioned magnetoelectric effects can be disentangled. Specifically, the large thickness of the Fe75Al25 layer allows dismissing any possible charge accumulation effect, whereas no evidence of magnetoionics is observed experimentally, as expected from the high resistance to oxidation of Fe75Al25, leaving strain as the only mechanism to modulate the asymmetric magnetoelectric response. The origin of this asymmetric strain-induced magnetoelectric effect arises from the asymmetry of the polarization reversal in the particular crystallographic orientation of the ferroelectric substrate. These results are important to optimize the performance of artificial multiferroic heterostructures. © 2019 American Physical Society.

  • Flexoelectric Fracture-Ratchet Effect in Ferroelectrics

    Cordero-Edwards K., Kianirad H., Canalias C., Sort J., Catalan G. Physical Review Letters; 122 (13, 135502) 2019. 10.1103/PhysRevLett.122.135502. IF: 9.227

    The propagation front of a crack generates large strain gradients and it is therefore a strong source of gradient-induced polarization (flexoelectricity). Herein, we demonstrate that, in piezoelectric materials, a consequence of flexoelectricity is that crack propagation is helped or hindered depending on whether it is parallel or antiparallel to the piezoelectric polar axis. The discovery of crack propagation asymmetry proves that fracture physics cannot be assumed to be symmetric in polar materials, and indicates that flexoelectricity should be incorporated in any realistic model. © 2019 American Physical Society.


  • 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

  • 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.

  • 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

  • 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

  • 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

  • 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.


  • Carborane bis-pyridylalcohols as linkers for coordination polymers: Synthesis, crystal structures, and guest-framework dependent mechanical properties

    Tsang M.Y., Rodríguez-Hermida S., Stylianou K.C., Tan F., Negi D., Teixidor F., Viñas C., Choquesillo-Lazarte D., Verdugo-Escamilla C., Guerrero M., Sort J., Juanhuix J., Maspoch D., Planas J.G. Crystal Growth and Design; 17 (2): 846 - 857. 2017. 10.1021/acs.cgd.6b01682. IF: 4.055

    We report the synthesis and characterization of six novel coordination polymers (CPs) based on M(II) (M: Zn and Co), di-, tri-, and tetracarboxylate linkers and two novel bis-pyridylalcohol 1,7-bis{(pyridin-n′-yl)methanol}-1,7-dicarba-closo-dodecaboranes (n′ = 3, L1; n′ = 4, L2) ligands. The polycarboxylates are terephthalic acid (H2BDC), 1,3,5-benzenetricarboxylic acid (H3BTB), and 1,2,4,5-Tetrakis(4-carboxyphenyl)benzene (H4TCPB). Structural description of CPs reveals the flexibility of the carborane ligands and their ability to construct extended structures. The CP containing Co(II), BTB, and L2 behaves as a crystalline sponge for a variety of guests, showing a higher affinity for aromatic guest molecules. Single-crystal nanoindentation experiments indicate that a high number of specific interactions between the guests and the CP framework result in a high elastic modulus and hardness values. © 2016 American Chemical Society.

  • Electric-Field-Adjustable Time-Dependent Magnetoelectric Response in Martensitic FeRh Alloy

    Fina I., Quintana A., Padilla-Pantoja J., Martí X., Macià F., Sánchez F., Foerster M., Aballe L., Fontcuberta J., Sort J. ACS Applied Materials and Interfaces; 9 (18): 15577 - 15582. 2017. 10.1021/acsami.7b00476. IF: 7.504

    Steady or dynamic magnetoelectric response, selectable and adjustable by only varying the amplitude of the applied electric field, is found in a multiferroic FeRh/PMN-PT device. In-operando time-dependent structural, ferroelectric, and magnetoelectric characterizations provide evidence that, as in magnetic shape memory martensitic alloys, the observed distinctive magnetoelectric responses are related to the time-dependent relative abundance of antiferromagnetic-ferromagnetic phases in FeRh, unbalanced by voltage-controlled strain. This flexible magnetoelectric response can be exploited not only for energy-efficient memory operations but also in other applications, where multilevel and/or transient responses are required. © 2017 American Chemical Society.

  • Ferroelectrics as Smart Mechanical Materials

    Cordero-Edwards K., Domingo N., Abdollahi A., Sort J., Catalan G. Advanced Materials; 29 (37, 1702210) 2017. 10.1002/adma.201702210. IF: 19.791

    The mechanical properties of materials are insensitive to space inversion, even when they are crystallographically asymmetric. In practice, this means that turning a piezoelectric crystal upside down or switching the polarization of a ferroelectric should not change its mechanical response. Strain gradients, however, introduce an additional source of asymmetry that has mechanical consequences. Using nanoindentation and contact-resonance force microscopy, this study demonstrates that the mechanical response to indentation of a uniaxial ferroelectric (LiNbO3) does change when its polarity is switched, and use this mechanical asymmetry both to quantify its flexoelectricity and to mechanically read the sign of its ferroelectric domains. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  • Hidden Magnetic States Emergent under Electric Field, in A Room Temperature Composite Magnetoelectric Multiferroic

    Clarkson J.D., Fina I., Liu Z.Q., Lee Y., Kim J., Frontera C., Cordero K., Wisotzki S., Sanchez F., Sort J., Hsu S.L., Ko C., Aballe L., Foerster M., Wu J., Christen H.M., Heron J.T., Schlom D.G., Salahuddin S., Kioussis N., Fontcuberta J., Marti X., Ramesh R. Scientific Reports; 7 (1, 15460) 2017. 10.1038/s41598-017-13760-y. IF: 4.259

    The ability to control a magnetic phase with an electric field is of great current interest for a variety of low power electronics in which the magnetic state is used either for information storage or logic operations. Over the past several years, there has been a considerable amount of research on pathways to control the direction of magnetization with an electric field. More recently, an alternative pathway involving the change of the magnetic state (ferromagnet to antiferromagnet) has been proposed. In this paper, we demonstrate electric field control of the Anomalous Hall Transport in a metamagnetic FeRh thin film, accompanying an antiferromagnet (AFM) to ferromagnet (FM) phase transition. This approach provides us with a pathway to "hide" or "reveal" a given ferromagnetic region at zero magnetic field. By converting the AFM phase into the FM phase, the stray field, and hence sensitivity to external fields, is decreased or eliminated. Using detailed structural analyses of FeRh films of varying crystalline quality and chemical order, we relate the direct nanoscale origins of this memory effect to site disorder as well as variations of the net magnetic anisotropy of FM nuclei. Our work opens pathways toward a new generation of antiferromagnetic - ferromagnetic interactions for spintronics. © 2017 The Author(s).

  • 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.

  • 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.

  • 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


  • 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.

  • 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.

  • 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.

  • 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.

  • 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.

  • 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.


  • 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.

  • 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.