Solis , Melisa Lara
Aguirre Yaccuzzi, Myriam Haydee (dir.)
Universidad de Zaragoza,
2025
Resumen: Desde el descubrimiento de la Magnetorresistencia Gigante (GMR) en 1988, la espintrónica ha avanzado rápidamente como un campo destinado a superar las limitaciones de la electrónica tradicional en velocidad, eficiencia energética y densidad de almacenamiento. Su enfoque central es aprovechar el espín, además de la carga eléctrica, lo que exige comprender cómo se genera, transporta y detecta el momento angular de espín.
Dentro de esta rama, los materiales aislantes con orden magnético ofrecen un enfoque prometedor para generar corrientes puras de espín, libres de pérdidas por disipación Joule. En estos sistemas, el transporte se realiza a través de excitaciones magnéticas colectivas conocidas como magnones. Este trabajo se dedica al estudio de la generación y detección de corrientes de espín en materiales granates, relevantes por su baja amortiguación y su larga longitud de propagación de espines. Para ello, se requiere profundizar en los mecanismos que regulan su transporte y mejorar su reproducibilidad para reducir costos.
La tesis investiga la generación de corrientes de espín coherentes mediante Resonancia Ferromagnética (FMR) e incoherentes mediante el Efecto Espín Seebeck (SSE) en nanoestructuras basadas en granate de itrio-hierro Y3Fe5O12 (YIG), tanto puro como dopado con bismuto BixY3-xFe5O12 (Bi:YIG). El SSE, central en la caloritrónica de espín, permite inducir corrientes magnónicas aplicando gradientes térmicos. La detección se realizó en bicapas granate/metal no magnético mediante el Efecto Espín Hall Inverso (ISHE), donde la interacción espín-órbita del metal convierte la corriente de espín en una señal eléctrica medible.
Las estrategias planteadas para mejorar la eficiencia de los dispositivos espintrónicos incluyen: (1) optimizar las nanoestructuras a nivel estructural, composicional y magnético; (2) generar corrientes de espín mediante magnones o excitaciones coherentes y (3) analizar la conversión interfacial de espín en carga. La primera parte del trabajo se centra en la fabricación de películas delgadas de YIG y Bi:YIG, así como de sus bicapas con platino, estudiando la influencia de las tensiones inducidas por los sustratos y del dopaje con bismuto sobre las propiedades magnéticas.
En la parte experimental se implementaron dos métodos para detectar el ISHE: uno basado en bombeo de espín mediante FMR (SP-FMR) y otro en la generación térmica por SSE. La detección del SSE se optimizó con el equipamiento disponible, mientras que para mejorar la repetibilidad se fabricaron microdispositivos litografiados en los que el calentamiento se produce por corriente eléctrica en una capa de oro sobre la nanoestructura Pt/granate. Se comparó la equivalencia de ambos métodos y se evaluaron sus ventajas y limitaciones. Para el SP-FMR se estudiaron dos técnicas: el uso de una cavidad resonante y una guía de onda coplanar (CPW) litografiada sobre el material. Finalmente, se analizaron las variaciones observadas entre muestras fabricadas en distintos laboratorios, incluso bajo condiciones idénticas, lo que sugiere nuevas posibilidades para controlar la funcionalidad de dispositivos basados en el ISHE y optimizar su desempeño.
Resumen (otro idioma): Since its discovery, marked by Giant Magnetoresistance (GMR) in 1988, the field of spintronics has rapidly evolved, giving rise to new research areas. Its ultimate goal is to develop a new approach capable of overcoming the limitations of conventional electronics in terms of speed, energy efficiency, and storage density. This approach is based on taking advantage of the degree of freedom associated with spin, in addition to electric charge. The study of spintronics requires addressing three fundamental aspects: the generation, transport, and detection of spin angular momentum. In this context, spin dynamics is the focus of intense research aimed at improving the efficiency of modern electronic devices. In particular, spintronics based on insulating materials with magnetic order offers a promising approach to generating pure spin currents. These currents, which are not accompanied by a charge current, allow spin propagation without losses due to Joule dissipation. Along these lines, spin carriers are collective magnetic excitations known as magnons. This thesis focuses on the study of the generation and detection of spin currents in insulating materials with garnet crystal structures. These materials are fundamental for the development of this area due to their low spin damping and long propagation length. However, it is necessary to deepen the understanding of the fundamental mechanisms that govern spin transport in these materials. Likewise, the fabrication and optimization of the materials to ensure their reproducibility constitutes a crucial aspect for reducing costs. The generation of coherent spin currents through Ferromagnetic Resonance (FMR) and incoherent ones through the Spin Seebeck Effect (SSE) was investigated in lowdimensional nanostructures based on yttrium iron garnets, both pure and substituted. The SSE is one of the most relevant transport phenomena in the field of spin caloritronics since it allows the direct generation of a magnonic spin current by applying a thermal gradient in magnetic materials. The detection of the spin currents generated was carried out in bilayers of garnet and non-magnetic metal through the Inverse Spin Hall Effect (ISHE), which arises from the spin-orbit interaction present in the metal used. The strategies proposed in this work to improve the efficiency of spintronic devices can be summarized as follows: (1) optimization of nanostructures at the structural, compositional, and magnetic levels, in order to study the relevant parameters; (2) generation of spin currents in the magnetic material, either through magnons or coherent spin excitations; and (3) analysis of the interfacial conversion of spin currents into detectable charge currents. The first part of this thesis focuses on the fabrication of thin films of garnet materials. In particular, the preparation of high-quality thin films of YIG (Y3Fe5O12) and bismuth-doped YIG (BixY3−xFe5O12) is studied. Additionally, the bilayers formed by these materials and platinum were investigated for the detection of spin currents through ISHE. The influence of substrate-induced stresses, whose garnet crystal structure matches that of the deposited materials, was analyzed, as well as how bismuth doping affects the magnetic properties of the films. In the experimental part, two methods were implemented to detect ISHE through coherent generation by Spin pumping by Ferromagnetic Resonance (SP-FMR) or incoherent by SSE. In the first case, an experiment was optimized using the equipment available in the laboratory to detect SSE. In the second case, microdevices were fabricated using optical lithography with the goal of improving the reproducibility of the experiments and increasing experimental precision. This alternative method is based on current-induced heating in a gold layer deposited on the Pt/garnet heterostructure. Finally, the experimental equivalence between both methods was analyzed, listing their advantages and disadvantages. For SP-FMR detection, two different methods were evaluated: one using a resonant cavity in FMR and another based on the design of a coplanar waveguide (CPW) directly lithographed onto the material. Despite the significant progress achieved in recent years, the structural complexity of these materials and the limited understanding of spintronic mechanisms at the interfaces have generated dispersion in published results and bottlenecks in advancing this technology. Consequently, this thesis focuses on the study of ISHE in these samples and the factors that influence its optimization. Additionally, the notable differences observed in materials fabricated in different laboratories, even under the same fabrication parameters, were analyzed. These differences pose the promising possibility of controlling the functionality of devices based on the spin Hall effect in insulating materials.
Dentro de esta rama, los materiales aislantes con orden magnético ofrecen un enfoque prometedor para generar corrientes puras de espín, libres de pérdidas por disipación Joule. En estos sistemas, el transporte se realiza a través de excitaciones magnéticas colectivas conocidas como magnones. Este trabajo se dedica al estudio de la generación y detección de corrientes de espín en materiales granates, relevantes por su baja amortiguación y su larga longitud de propagación de espines. Para ello, se requiere profundizar en los mecanismos que regulan su transporte y mejorar su reproducibilidad para reducir costos.
La tesis investiga la generación de corrientes de espín coherentes mediante Resonancia Ferromagnética (FMR) e incoherentes mediante el Efecto Espín Seebeck (SSE) en nanoestructuras basadas en granate de itrio-hierro Y3Fe5O12 (YIG), tanto puro como dopado con bismuto BixY3-xFe5O12 (Bi:YIG). El SSE, central en la caloritrónica de espín, permite inducir corrientes magnónicas aplicando gradientes térmicos. La detección se realizó en bicapas granate/metal no magnético mediante el Efecto Espín Hall Inverso (ISHE), donde la interacción espín-órbita del metal convierte la corriente de espín en una señal eléctrica medible.
Las estrategias planteadas para mejorar la eficiencia de los dispositivos espintrónicos incluyen: (1) optimizar las nanoestructuras a nivel estructural, composicional y magnético; (2) generar corrientes de espín mediante magnones o excitaciones coherentes y (3) analizar la conversión interfacial de espín en carga. La primera parte del trabajo se centra en la fabricación de películas delgadas de YIG y Bi:YIG, así como de sus bicapas con platino, estudiando la influencia de las tensiones inducidas por los sustratos y del dopaje con bismuto sobre las propiedades magnéticas.
En la parte experimental se implementaron dos métodos para detectar el ISHE: uno basado en bombeo de espín mediante FMR (SP-FMR) y otro en la generación térmica por SSE. La detección del SSE se optimizó con el equipamiento disponible, mientras que para mejorar la repetibilidad se fabricaron microdispositivos litografiados en los que el calentamiento se produce por corriente eléctrica en una capa de oro sobre la nanoestructura Pt/granate. Se comparó la equivalencia de ambos métodos y se evaluaron sus ventajas y limitaciones. Para el SP-FMR se estudiaron dos técnicas: el uso de una cavidad resonante y una guía de onda coplanar (CPW) litografiada sobre el material. Finalmente, se analizaron las variaciones observadas entre muestras fabricadas en distintos laboratorios, incluso bajo condiciones idénticas, lo que sugiere nuevas posibilidades para controlar la funcionalidad de dispositivos basados en el ISHE y optimizar su desempeño.
Resumen (otro idioma): Since its discovery, marked by Giant Magnetoresistance (GMR) in 1988, the field of spintronics has rapidly evolved, giving rise to new research areas. Its ultimate goal is to develop a new approach capable of overcoming the limitations of conventional electronics in terms of speed, energy efficiency, and storage density. This approach is based on taking advantage of the degree of freedom associated with spin, in addition to electric charge. The study of spintronics requires addressing three fundamental aspects: the generation, transport, and detection of spin angular momentum. In this context, spin dynamics is the focus of intense research aimed at improving the efficiency of modern electronic devices. In particular, spintronics based on insulating materials with magnetic order offers a promising approach to generating pure spin currents. These currents, which are not accompanied by a charge current, allow spin propagation without losses due to Joule dissipation. Along these lines, spin carriers are collective magnetic excitations known as magnons. This thesis focuses on the study of the generation and detection of spin currents in insulating materials with garnet crystal structures. These materials are fundamental for the development of this area due to their low spin damping and long propagation length. However, it is necessary to deepen the understanding of the fundamental mechanisms that govern spin transport in these materials. Likewise, the fabrication and optimization of the materials to ensure their reproducibility constitutes a crucial aspect for reducing costs. The generation of coherent spin currents through Ferromagnetic Resonance (FMR) and incoherent ones through the Spin Seebeck Effect (SSE) was investigated in lowdimensional nanostructures based on yttrium iron garnets, both pure and substituted. The SSE is one of the most relevant transport phenomena in the field of spin caloritronics since it allows the direct generation of a magnonic spin current by applying a thermal gradient in magnetic materials. The detection of the spin currents generated was carried out in bilayers of garnet and non-magnetic metal through the Inverse Spin Hall Effect (ISHE), which arises from the spin-orbit interaction present in the metal used. The strategies proposed in this work to improve the efficiency of spintronic devices can be summarized as follows: (1) optimization of nanostructures at the structural, compositional, and magnetic levels, in order to study the relevant parameters; (2) generation of spin currents in the magnetic material, either through magnons or coherent spin excitations; and (3) analysis of the interfacial conversion of spin currents into detectable charge currents. The first part of this thesis focuses on the fabrication of thin films of garnet materials. In particular, the preparation of high-quality thin films of YIG (Y3Fe5O12) and bismuth-doped YIG (BixY3−xFe5O12) is studied. Additionally, the bilayers formed by these materials and platinum were investigated for the detection of spin currents through ISHE. The influence of substrate-induced stresses, whose garnet crystal structure matches that of the deposited materials, was analyzed, as well as how bismuth doping affects the magnetic properties of the films. In the experimental part, two methods were implemented to detect ISHE through coherent generation by Spin pumping by Ferromagnetic Resonance (SP-FMR) or incoherent by SSE. In the first case, an experiment was optimized using the equipment available in the laboratory to detect SSE. In the second case, microdevices were fabricated using optical lithography with the goal of improving the reproducibility of the experiments and increasing experimental precision. This alternative method is based on current-induced heating in a gold layer deposited on the Pt/garnet heterostructure. Finally, the experimental equivalence between both methods was analyzed, listing their advantages and disadvantages. For SP-FMR detection, two different methods were evaluated: one using a resonant cavity in FMR and another based on the design of a coplanar waveguide (CPW) directly lithographed onto the material. Despite the significant progress achieved in recent years, the structural complexity of these materials and the limited understanding of spintronic mechanisms at the interfaces have generated dispersion in published results and bottlenecks in advancing this technology. Consequently, this thesis focuses on the study of ISHE in these samples and the factors that influence its optimization. Additionally, the notable differences observed in materials fabricated in different laboratories, even under the same fabrication parameters, were analyzed. These differences pose the promising possibility of controlling the functionality of devices based on the spin Hall effect in insulating materials.
Pal. clave: espintrónica ; bombeo de espín ; efecto espín-hall inverso (ishe) ; efecto espín-seebeck (sse) ; granate de itrio-hierro (yig)
Titulación: Programa de Doctorado en Física
Plan(es): Plan 488
Área de conocimiento: Ciencias
Nota: Presentado: 18 12 2025
Nota: Tesis-Univ. Zaragoza, , 2025
Aportación del TFG/M a la Sostenibilidad: Desarrollar infraestructuras resilientes, promover la industrialización inclusiva y sostenible, y fomentar la innovación.
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