Structure and dynamics of magnetic domain walls in multi-sublattice magnetic oxides
| Autor: | Huang, Siying |
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| Rok vydání: | 2024 |
| Druh dokumentu: | Diplomová práce |
| Popis: | Spintronics is a study that lies at the intersection of magnetics and electronics, which makes use of the electron spin in solid-state devices for data storage and manipulation. A promising future spintronic technology is racetrack memory, where magnetic domain walls (DWs) are encoded with bits of information and are translated by currents on thin-film racetrack devices. What enables the current-driven motion of the DW is its Néel character, generally stabilized by the Dzyaloshinskii–Moriya interaction (DMI). Fast DW motion of the order of km/s was shown in multi-sublattice metallic systems, overcoming the fundamental limits in ferromagnetic systems through angular momentum compensation of the sublattices. Recently, DMI and even faster DW motion have been observed in thin-film rare-earth iron garnets. However, the net angular momentum in such systems is shown to be far from angular momentum compensation. Moreover, the mechanism of the DMI in garnets is shown to be distinct from the metallic systems, thus requiring further understanding as well. In this thesis, we examine magnetic DWs in such multi-sublattice magnetic oxides. We demonstrate a strong tunability of the DMI by a factor of 7 through the substrate in Pt/garnet thin f ilms, providing further understanding of the DMI mechanism. For the anomalously fast DW motion, we present an explanation by the field-like torque counteracting the damping-like torque and increasing the spin Hall efficiency. We propose measuring the DW velocity with a transverse field applied to probe this field-like torque, and present experimental evidence. We investigated the DW depinning dynamics in Pt/BiYIG thin film, presenting a phase diagram of this pinning event, which proves the crucial role of minimizing the pinning effect in achieving fast DW velocity. In EuIG(110) thin film with strong in-plane anisotropy, we demonstrate bistable Néel DW states interchangeable by in-plane field pulse-driven incoherent DW reversal, from which we extract for the first time the Bloch line energetics. Besides the above DW Néel character stabilization, we also provide a DW position stabilization on the racetracks by the exchange bias effect in Pt/Co/Pt/Co₀.₈Ni₀.₂O thin films. This thesis provides a comprehensive understanding of the stability and dynamics of DWs on racetrack devices based on magnetic oxides, from the aspects of both scientific understanding and technical optimizations, paving a path to future innovation and optimization in racetrack memory device design. Ph.D. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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