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    Spin Orbit Torque in Ferromagnetic Semiconductors

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    Name:
    Hang Li - Dissertation - Final Draft.pdf
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    Type
    Dissertation
    Authors
    Li, Hang cc
    Advisors
    Manchon, Aurelien cc
    Committee members
    Schwingenschlögl, Udo cc
    Li, Xiaohang cc
    Duine, Rembert A.
    Program
    Materials Science and Engineering
    KAUST Department
    Physical Science and Engineering (PSE) Division
    Date
    2016-06-21
    Embargo End Date
    2017-06-15
    Permanent link to this record
    http://hdl.handle.net/10754/614071
    
    Metadata
    Show full item record
    Access Restrictions
    At the time of archiving, the student author of this dissertation opted to temporarily restrict access to it. The full text of this dissertation became available to the public after the expiration of the embargo on 2017-06-15.
    Abstract
    Electrons not only have charges but also have spin. By utilizing the electron spin, the energy consumption of electronic devices can be reduced, their size can be scaled down and the efficiency of `read' and `write' in memory devices can be significantly improved. Hence, the manipulation of electron spin in electronic devices becomes more and more appealing for the advancement of microelectronics. In spin-based devices, the manipulation of ferromagnetic order parameter using electrical currents is a very useful means for current-driven operation. Nowadays, most of magnetic memory devices are based on the so-called spin transfer torque, which stems from the spin angular momentum transfer between a spin-polarized current and the magnetic order parameter. Recently, a novel spin torque effect, exploiting spin-orbit coupling in non-centrosymmetric magnets, has attracted a massive amount of attention. This thesis addresses the nature of spin-orbit coupled transport and torques in non-centrosymmetric magnetic semiconductors. We start with the theoretical study of spin orbit torque in three dimensional ferromagnetic GaMnAs. Using the Kubo formula, we calculate both the current-driven field-like torque and anti-damping-like torque. We compare the numerical results with the analytical expressions in the model case of a magnetic Rashba two-dimensional electron gas. Parametric dependencies of the different torque components and similarities to the analytical results of the Rashba two-dimensional electron gas in the weak disorder limit are described. Subsequently we study spin-orbit torques in two dimensional hexagonal crystals such as graphene, silicene, germanene and stanene. In the presence of staggered potential and exchange field, the valley degeneracy can be lifted and we obtain a valley-dependent Berry curvature, leading to a tunable antidamping torque by controlling the valley degree of freedom. This thesis then addresses the influence of the quantum spin Hall effect on spin orbit torque in nanoribbons with a hexagonal lattice. We find a dramatic modification of the nature of the torque (field like and damping-like component) when crossing the topological phase transition. The relative agnitude of the two torque components can be significantly modifies by changing the magnetization direction. Finally, motivated by recent experimental results, we conclude by investigating the features of spin-orbit torque in magnetic transition metal dichalcogenides. We find the torque is associated with the valley polarization. By changing the magnetization direction, the torque can be changed from a finite value to zero when the valley polarization decreases from a finite value to zero.
    Citation
    Li, H. (2016). Spin Orbit Torque in Ferromagnetic Semiconductors. KAUST Research Repository. https://doi.org/10.25781/KAUST-S464K
    DOI
    10.25781/KAUST-S464K
    ae974a485f413a2113503eed53cd6c53
    10.25781/KAUST-S464K
    Scopus Count
    Collections
    PhD Dissertations; Physical Science and Engineering (PSE) Division; Material Science and Engineering Program

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