Integración de láminas delgadas de materiales feromagnéticos medio-metálicos en silicio por medio de un contacto túnel

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Física de Materiales, leída el 08-07-2019The use of magnetic tunnel contacts have been proved as one of the most efficient methods for the efficient injection and detection of spin polarized currents on non-magnetic semiconductors. In this kind of systems, the spin polarized carriers of the ferromagnetic electrode are transferred by tunneling through an insulator barrier into the semiconductor. The diusive transport directly through the ferromagnet/semiconductor interface is limited by the large impedance mismatch between the two materials. The introduction of a tunnel barrier allows to improve the efficiency of the system and increase spin accumulation in the semiconductor. However, in order to achieve high spin rates the system needs to ful ll certain requirements. One of the fundamental conditions is the formation of at and abrupt interfaces. High interface roughness can induce the presence of magnetostatic elds that might induce spin precession and reduce spin polarization. Moreover, the presence of defects on the interface can act as scattering centers and reduce even more spin accumulation in the semiconductor...Se ha demostrado que el uso de contactos tunel magneticos es uno de los metodos mas eficientes para la inyeccion y deteccion de corrientes polarizadas en espín en semiconductores no magneticos. En este tipo de sistemas, los portadores de carga polarizados en espín del electrodo ferromagnetico se transfieren al semiconductor por efecto tunel a traves de una barrera aislante. La inyeccion de espín por transporte difusivo de forma directa a traves de la intercara ferromagnetico/aislante es muy poco eficiente en terminos de polarizacion debido a la gran diferencia de impedancia electrica entre los dos materiales. La introduccion de una barrera tunel permite mejorar la eficiencia del sistema y aumentar la acumulacion de espín en el semiconductor. Sin embargo, para poder obtener una inyeccion eficiente el sistema debe ademas cumplir ciertos requisitos. Una de las condiciones principales es que las heteroestructuras presenten intercaras abruptas tanto morfologicamente como desde el punto de vista qumico. Esto se debe a que una rugosidad alta puede generar campos magnetoestaticos en la intercara que induzcan la precesion de los espines y reduzcan la polarizacion en el semiconductor. Ademas, los defectos presentes en la intercara pueden funcionar como centros de dispersion y reducir a su vez la polarizacion en espín de los portadores...Fac. de Ciencias FísicasTRUEunpu

Isotropic spin and inverse spin Hall effect in epitaxial (111)-oriented Pt/Co bilayers

The spin-to-charge current interconversion in bilayers composed of ferromagnetic and nonmagnetic layers with strong spin-orbit coupling has garnered considerable attention due to its exceptional potential in advancing spintronics devices for data storage and logic applications. Platinum (Pt) stands out as one of the most effective materials for generating spin current. While the spin conversion efficiency is isotropic in polycrystalline Pt samples, an ongoing debate persists regarding its dependence on the crystalline direction in single crystalline samples. In this study, we aim to comprehensively evaluate the in-plane anisotropy of spin-charge interconversion using an array of complementary Spin Hall and inverse Spin Hall techniques with both incoherent and coherent excitation. Specifically, we investigate the spin-to-charge interconversion in epitaxial, (111)-oriented, Co/Pt bilayers with low surface roughness, as resulted from x-ray experiments. By varying the thickness of the Pt layer, we gain insights into the spin-charge interconversion in epitaxial Pt and highlight the effects of the interfaces. Our results demonstrate an isotropic behavior within the limits of our detection uncertainty. This finding significantly enhances our understanding of spin conversion in one of the most relevant systems in spintronics and paves the way for future research in this field.Comment: Article accepted for publication in Physical Review Materials, DOI not received ye

Improving the co and ch4 gas sensor response at room temperature of alpha-fe2o3(0001) epitaxial thin films grown on srtio3(111) incorporating au(111) islands

In this work, the functional character of complex -Fe2O3(0001)/SrTiO3(111) and Au(111) islands/ -Fe2O3(0001)/SrTiO3(111) heterostructures has been proven as gas sensors at room temperature. Epitaxial Au islands and -Fe2O3 thin film are grown by pulsed laser deposition on SrTiO3(111) substrates. Intrinsic parameters such as the composition, particle size and epitaxial character are investigated for their influence on the gas sensing response. Both Au and -Fe2O3 layer show an island-type growth with an average particle size of 40 and 62 nm, respectively. The epitaxial and incommensurate growth is evidenced, confirming a rotation of 30 between the in-plane crystallographic axes of -Fe2O3(0001) structure and those of SrTiO3(111) substrate and between the in-plane crystallographic axes of Au(111) and those of -Fe2O3(0001) structure. -Fe2O3 is the only phase of iron oxide identified before and after its functionalization with Au nanoparticles. In addition, its structural characteristics are also preserved after Au deposition, with minor changes at short-range order. Conductance measurements of Au(111)/ -Fe2O3(0001)/SrTiO3(111) system show that the incorporation of epitaxial Au islands on top of the -Fe2O3(0001) layer induces an enhancement of the gas-sensing activity of around 25% under CO and 35% under CH4 gas exposure, in comparison to a bare -Fe2O3(0001) layer grown on SrTiO3(111) substrates. In addition, the response of the heterostructures to CO gas exposure is around 5–10% higher than to CH4 gas in each case.This work has been supported by the Ministerio Español de Ciencia e Innovación (MICINN) and the Consejo Superior de Investigaciones Cientificas (CSIC) through the projects PIE-2010-OE-013- 200014, PIE 2021-60-E-030 and RTI2018-095303-A-C52. The ESRF, MICINN and CSIC are acknowledged for the provision of synchrotron radiation facilities. A.S. acknowledges financial support from Comunidad de Madrid for an “Atracción de Talento Investigador” Contract (2017-t2/IND5395)

Stabilization of Epitaxial α‑Fe₂O₃ Thin Films Grown by Pulsed Laser Deposition on Oxide Substrates

We have grown epitaxial incommensurate α-Fe₂O₃ thin films on α-Al₂O₃(0001), SrTiO₃(111), and LaAlO₃(001) substrates, identifying hematite as single iron oxide phase stabilized. We demonstrate that a different lattice coupling behavior as a function of the selected oxide substrate mediates the epitaxial character. Single-oriented α-Fe₂O₃(0001) layers are obtained on α-Al₂O₃(0001) and SrTiO₃(111) substrates, whereas on the LaAlO₃(001) substrate, the hematite layer is found to grow along the <i>r</i>-plane to adapt its hexagonal lattice on the cubic lattice of the substrate, evidencing a single-oriented (11̅02) layer. In the film plane, crystallographic axes of α-Fe₂O₃(0001) are collinear with the α-Al₂O₃(0001) ones, while a rotation of 30° is found between those of α-Fe₂O₃(0001) and SrTiO₃(111). On LaAlO₃(001), α-Fe₂O₃(11̅02) adopts an in-plane orthorhombic structure rotated 45° respect to the substrate lattice. The crystallographic domain size and the crystalline order are dependent on the incommensurate lattice coupling mechanism. Larger values are obtained for layers grown on α-Al₂O₃(0001), while lower values correspond to the hematite deposited on LaAlO₃(001). Moreover, an Fe–O elongation and Fe–Fe contraction of first neighbors distances as well as a dependency on surface flatness as a function of the substrate lattice parameter is also found

Toward nonvolatile spin-orbit devices: deposition of ferroelectric hafnia on monolayer graphene/Co/HM stacks

“This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Applied Materials and Interfaces, copyright © American Chemical Society after peer review and technical editing by the publisher. To acces final work see “Toward nonvolatile spin-orbit devices: deposition of ferroelectric hafnia on monolayer graphene/Co/HM stacks”, ACS Applied Materials and Interfaces 15.13 (2023): 16963-16974, DOI: 10.1021/acsami.2c22205“While technologically challenging, the integration of ferroelectric thin films with graphene spintronics potentially allows the realization of highly efficient, electrically tunable, nonvolatile memories through control of the interfacial spin-orbit driven interaction occurring at graphene/Co interfaces deposited on heavy metal supports. Here, the integration of ferroelectric Hf0.5Zr0.5O2 on graphene/Co/heavy metal epitaxial stacks is investigated via the implementation of several nucleation methods in atomic layer deposition. By employing in situ Al2O3 as a nucleation layer sandwiched between Hf0.5Zr0.5O2 and graphene, the Hf0.5Zr0.5O2 demonstrates a remanent polarization (2Pr) of 19.2 μC/cm2. Using an ex situ, naturally oxidized sputtered Ta layer for nucleation, we could control 2Pr via the interlayer thickness, reaching maximum values of 28 μC/cm2 with low coercive fields. Magnetic hysteresis measurements taken before and after atomic layer deposition show strong perpendicular magnetic anisotropy, with minimal deviations in the magnetization reversal pathways due to the Hf0.5Zr0.5O2 deposition process, thus pointing to a good preservation of the magnetic stack including single-layer graphene. X-ray diffraction measurements further confirm that the high-quality interfaces demonstrated in the stack remain unperturbed by the ferroelectric deposition and anneal. The proposed graphene-based ferroelectric/magnetic structures offer the strong advantages of ferroelectricity and ferromagnetism at room temperature, enabling the development of novel magneto-electric and nonvolatile in-memory spin-orbit logic architectures with low power switchingThis project has received funding from the FLAG-ERA JTC 2019 grant SOgraphMEM through the partner’s national research agencies AEI/MICINN (Spain, PCI2019-111867-2) and DFG (Germany, MI 1247/18-1). The IMDEA team acknowledges support by the Community of Madrid (CM) through project P2018/NMT-4321 (NANOMAGCOST), by MICINN through projects RTI2018-097895-B-C42, 43 (FUN-SOC), and PID2021-122980OB-C51,52 (ECLIPSE), and by the “Severo Ochoa” Programme for Centres of Excellence in R&D CEX2020-001039-S. A.G. and I.A. ackowledge support from CM (PEJD-2017-PREIND-4690 and PEJD-2019-POST/IND-15343) and JMD from MICINN (BES 2017-080617