Complex Oxide Heterostructures for Spin Electronics
[eng] The direct manipulation of spin currents with no charges involved along with the delicate interplay between charge, spin and orbital degrees of freedom in materials and structures has attracted a renewed interest in the last few years. Technologically speaking, one of the most attractive featu...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2022 |
| País: | España |
| Institución: | Universidad de Barcelona |
| Repositorio: | Dipòsit Digital de la UB |
| OAI Identifier: | oai:diposit.ub.edu:2445/189856 |
| Acceso en línea: | https://hdl.handle.net/2445/189856 http://hdl.handle.net/10803/675683 |
| Access Level: | acceso abierto |
| Palabra clave: | Espintrònica Òxids Pel·lícules fines Spintronics Oxides Thin films |
| Sumario: | [eng] The direct manipulation of spin currents with no charges involved along with the delicate interplay between charge, spin and orbital degrees of freedom in materials and structures has attracted a renewed interest in the last few years. Technologically speaking, one of the most attractive features of pure spin currents is the disappearance of Joule heating, which is directly linked to the amazing problem of heat dissipation in today’s microelectronic devices. As such, the generation, manipulation, and detection of pure spin currents is still one of the major challenges in spintronics nowadays. In this regard, the charge-to-spin current interconversion processes play a very relevant role and having the set of materials and structures that maximize these processes is of paramount importance. In this Thesis, the generation, manipulation, and detection of pure spin currents in ferromagnetic/normal metal bilayers is addressed. The use of manganese-based complex oxide perovskites is especially relevant: complex oxide materials are very appealing from the technological viewpoint due to their inherent multifunctional nature. The capabilities and versatility of ferromagnetic resonance (FMR) spectroscopy for disclosing the crucial magnetodynamical parameters of our samples are foreseen by first studying the archetypal bilayer composed by Ni80Fe20/Pt. Simultaneously, since the generation of pure spin currents by means of spin pumping is also triggered by microwave absorption during FMR, the effective generation of pure spin currents is demonstrated via ISHE in ferromagnetic/normal metal bilayers. The generated pure spin current is converted to a transverse charge current (via ISHE) in the high spin-orbit coupling (SOC) Pt capping layer and detected as a transverse voltage difference across the film. In this Thesis, the dual nature of FMR spectroscopy is highlighted and a novel method for suppressing parasitic voltage contributions to the overall ISHE voltage signal is presented. Finally, in order to gain insight into the behavior of these parasitic effects, a numerical study based on our actual experimental system is performed. The suitability as spin current injectors/detectors of three different complex oxide heterostructures, namely La0.92MnO3 (LMO)/Pt, La2/3Sr1/3MnO3 (LSMO)/Pt and LSMO/SrIrO3 (SIO), is also investigated. The latter is especially relevant in the context of this Thesis for it is the only all-oxide complex structure evaluated. Unlike any other film studied, LMO films were prepared by polymer assisted deposition. In this regard, there has been some concerns regarding the suitability of chemically deposited thin films for challenging applications which require microstructural quality and sharp interfaces, as in spintronics. Nevertheless, the structural high-quality and efficient spin injection capabilities of chemically deposited LMO films for a wide range of temperatures are demonstrated. Similarly, the spin injection performance of sputtered LSMO films in LSMO/Pt bilayer systems is shown. In a second step, a material with presumably large SOC, such as SIO, is introduced as spin detector, and the spin injection/detection processes in the all-oxide heterostructure LSMO/SIO are addressed. In this case, it is demonstrated the promising role of SIO as an efficient spin-to-charge converter, thus opening the door to the development of high-quality spin-to-charge conversion devices based on all-oxide heterostructures. Finally, this Thesis also focuses on the measurement of a rather different spintronic effect: spin Hall magnetoresistance (SMR). In this magnetoresistive effect, a pure spin current is generated via spin Hall effect (SHE) in Pt and directed towards the La2CoMnO6 (LCMO)/Pt interface. The interaction between this spin current and the magnetization of the ferromagnetic insulating thin LCMO film is at the heart of SMR. The experimental observations exemplify the exceptional role played by the interface. Additionally, a theoretical model is employed for interpreting the results and it is inferred that the magnetic state of the uppermost layers of the LCMO film are actually magnetically decoupled from the rest of the film, exhibiting a behavior compatible with a 2D Heisenberg ferromagnet, with no long-range magnetic order nor transition temperature. |
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