Staff directory Adriana Isabel Figueroa García

Adriana Isabel Figueroa García

Postdoctoral Researcher
Physics and Engineering of Nanodevices



  • Absence of Magnetic Proximity Effect at the Interface of Bi2Se3 and (Bi,Sb)2Te3 with EuS

    Figueroa A.I., Bonell F., Cuxart M.G., Valvidares M., Gargiani P., Van Der Laan G., Mugarza A., Valenzuela S.O. Physical Review Letters; 125 (22, 226801) 2020. 10.1103/PhysRevLett.125.226801. IF: 8.385

    We performed X-ray magnetic circular dichroism (XMCD) measurements on heterostructures comprising topological insulators (TIs) of the (Bi,Sb)2(Se,Te)3 family and the magnetic insulator EuS. XMCD measurements allow us to investigate element-selective magnetic proximity effects at the very TI/EuS interface. A systematic analysis reveals that there is neither significant induced magnetism within the TI nor an enhancement of the Eu magnetic moment at such interface. The induced magnetic moments in Bi, Sb, Te, and Se sites are lower than the estimated detection limit of the XMCD measurements of ∼10-3 μB/at. © 2020 American Physical Society.

  • Control of Spin-Orbit Torques by Interface Engineering in Topological Insulator Heterostructures

    Bonell F., Goto M., Sauthier G., Sierra J.F., Figueroa A.I., Costache M.V., Miwa S., Suzuki Y., Valenzuela S.O. Nano Letters; 20 (8): 5893 - 5899. 2020. 10.1021/acs.nanolett.0c01850. IF: 11.238

    (Bi1-xSbx)2Te3 topological insulators (TIs) are gathering increasing attention owing to their large charge-to-spin conversion efficiency and the ensuing spin-orbit torques (SOTs) that can be used to manipulate the magnetization of a ferromagnet (FM). The origin of the torques, however, remains elusive, while the implications of hybridized states and the strong material intermixing at the TI/FM interface are essentially unexplored. By combining interface chemical analysis and spin-transfer ferromagnetic resonance (ST-FMR) measurements, we demonstrate that intermixing plays a critical role in the generation of SOTs. By inserting a suitable normal metal spacer, material intermixing is reduced and the TI properties at the interface are largely improved, resulting in strong variations in the nature of the SOTs. A dramatic enhancement of a field-like torque, opposing and surpassing the Oersted-field torque, is observed, which can be attributed to the non-equilibrium spin density in Rashba-split surface bands and to the suppression of spin memory loss. These phenomena can play a relevant role at other interfaces, such as those comprising transition metal dichalcogenides. © 2020 American Chemical Society.

  • Element- and Time-Resolved Measurements of Spin Dynamics Using X-ray Detected Ferromagnetic Resonance

    Klewe C., Li Q., Yang M., N’Diaye A.T., Burn D.M., Hesjedal T., Figueroa A.I., Hwang C., Li J., Hicken R.J., Shafer P., Arenholz E., van der Laan G., Qiu Z. Synchrotron Radiation News; 33 (2): 12 - 19. 2020. 10.1080/08940886.2020.1725796. IF: 0.000

    [No abstract available]

  • Magnetic order in 3D topological insulators-Wishful thinking or gateway to emergent quantumeffects?

    Figueroa A.I., Hesjedal T., Steinke N.-J. Applied Physics Letters; 117 (15, 0027987) 2020. 10.1063/5.0027987. IF: 3.597

    Three-dimensional topological insulators (TIs) are a perfectly tuned quantum-mechanical machinery in which counterpropagating and oppositely spin-polarized conduction channels balance each other on the surface of the material. This topological surface state crosses the bandgap of the TI and lives at the interface between the topological and a trivial material, such as vacuum. Despite its balanced perfection, it is rather useless for any practical applications. Instead, it takes the breaking of time-reversal symmetry (TRS) and the appearance of an exchange gap to unlock hidden quantum states. The quantum anomalous Hall effect, which has first been observed in Cr-doped (Sb,Bi)2Te3, is an example of such a state in which two edge channels are formed at zero field, crossing the magnetic exchange gap. The breaking of TRS can be achieved by magnetic doping of the TI with transition metal or rare earth ions, modulation doping to keep the electronically active channel impurity free, or proximity coupling to a magnetically ordered layer or substrate in heterostructures or superlattices. We review the challenges these approaches are facing in the famous 3D TI (Sb,Bi)2(Se,Te)3 family and try to answer the question whether these materials can live up to the hype surrounding them. © 2020 BMJ Publishing Group. All rights reserved.


  • A brief discussion of the magnetocaloric effect in thin films of manganite doped with chromium

    Campillo G., Figueroa A.I., Arnache O., Osorio J., Marin Ramirez J.M., Fallarino L. Journal of Physics: Conference Series; 1247 (1, 012013) 2019. 10.1088/1742-6596/1247/1/012013.

    In this work we report on the magnetocaloric effect of La2/3Ca1/3MnO3 (LCMO) and La2/3Ca1/3Mn0.94Cr0.06O3 (LCMCrO) manganite thin films grown by DC magnetron sputtering on LaAlO3 (100) substrates. X-ray diffraction shows that both doped and undoped films crystallize in the orthorhombic structure. Magnetic measurements show a decrease in both the Curie temperature, TC , and the saturation magnetization, MS , for the LCMCrO sample. The change in the magnetic entropy (ΔSm ) was extracted from hysteresis loops at different temperatures around the ferromagnetic to paramagnetic transition, displaying a maximum of entropy change (ΔSm ) max near TC in both films. Moreover, a shift in (ΔSm ) max toward temperatures above TC with increasing magnetic field and a broadening of the entropy change curve were observed. Results of refrigeration cooling power show a lower efficiency for LCMCrO. In order to obtain a local insight into the magnetic interactions of these films, measurements of X-ray absorption spectroscopy and X-ray magnetic circular dichroism (XMCD) were performed. XMCD suggests that an antiferromagnetic coupling between Mn4+ - Mn3+ is favored with Cr3+ incorporation, which reduces the Mn L 2,3 XMCD signal and results in a decrease of MS and (ΔSm ) max in LCMCrO films. © Published under licence by IOP Publishing Ltd.

  • Cr2Te3 Thin Films for Integration in Magnetic Topological Insulator Heterostructures

    Burn D.M., Duffy L.B., Fujita R., Zhang S.L., Figueroa A.I., Herrero-Martin J., van der Laan G., Hesjedal T. Scientific Reports; 9 (1, 10793) 2019. 10.1038/s41598-019-47265-7. IF: 4.011

    Chromium telluride compounds are promising ferromagnets for proximity coupling to magnetic topological insulators (MTIs) of the Cr-doped (Bi,Sb)2(Se,Te)3 class of materials as they share the same elements, thus simplifying thin film growth, as well as due to their compatible crystal structure. Recently, it has been demonstrated that high quality (001)-oriented Cr2Te3 thin films with perpendicular magnetic anisotropy can be grown on c-plane sapphire substrate. Here, we present a magnetic and soft x-ray absorption spectroscopy study of the chemical and magnetic properties of Cr2Te3 thin films. X-ray magnetic circular dichroism (XMCD) measured at the Cr L2,3 edges gives information about the local electronic and magnetic structure of the Cr ions. We further demonstrate the overgrowth of Cr2Te3 (001) thin films by high-quality Cr-doped Sb2Te3 films. The magnetic properties of the layers have been characterized and our results provide a starting point for refining the physical models of the complex magnetic ordering in Cr2Te3 thin films, and their integration into advanced MTI heterostructures for quantum device applications. © 2019, The Author(s).