Open Access

Sebastian Tölle

• Spintronics is an emerging field with the central objective of utilizing simultaneously the spin and charge degrees of freedom. The exploitation of the spin, in addition to the charge, offers the opportunity to overcome limitations of traditional electronics, especially for data storage and transfer. In this context, the fundamental tasks are the generation, manipulation, and detection of spin densities and spin currents. Experimentally, an implementation of these tasks can be achieved by attaching a spin-orbit active material to a ferromagnet. Particularly interesting examples of spin-orbit active materials are systems with Rashba spin-orbit coupling. In this thesis, we theoretically investigate the spin-charge coupled dynamics in such systems for three special geometries. First, a quasi two-dimensional Rashba system with a proximity induced magnetization is considered. Due to a dynamical magnetic texture an effective force acting on the charge carriers is found. We identify eachSpintronics is an emerging field with the central objective of utilizing simultaneously the spin and charge degrees of freedom. The exploitation of the spin, in addition to the charge, offers the opportunity to overcome limitations of traditional electronics, especially for data storage and transfer. In this context, the fundamental tasks are the generation, manipulation, and detection of spin densities and spin currents. Experimentally, an implementation of these tasks can be achieved by attaching a spin-orbit active material to a ferromagnet. Particularly interesting examples of spin-orbit active materials are systems with Rashba spin-orbit coupling. In this thesis, we theoretically investigate the spin-charge coupled dynamics in such systems for three special geometries. First, a quasi two-dimensional Rashba system with a proximity induced magnetization is considered. Due to a dynamical magnetic texture an effective force acting on the charge carriers is found. We identify each contribution by its origin, spin density or spin current, highlighting a novel 'inverse-spin-filter' contribution. The latter arises from a spin current polarized parallel to the magnetization as a result of a consistent treatment of spin-orbit contributions to the Elliott-Yafet spin relaxation mechanism. In the second geometry, a two-dimensional Rashba system laterally attached to a ferromagnet, the boundary conditions at the interface are significantly affected by current-induced spin polarizations. Therefore, the magnetization-dependence of the magnetoresistance is non-trivial and asymmetric, and, in particular, features a characteristic magnetization angle where the ferromagnetic contribution to the magnetoresistance vanishes. The thermal analogue of the magnetoresistance, the magnetothermopower, turns out to be very small due to a cancellation of electrical and thermal contributions. The Rashba system in the third setup is extended to the third dimension, and placed on top of a ferromagnetic insulator. Due to the spin-transfer torque, the current-induced spin polarization acquires a characteristic magnetization dependence which manifests itself in the signal of the magnetoresistance. Our theoretical results reproduce several features of the experiments, at least qualitatively. In particular, the anisotropy of the spin relaxation, enhanced due to the mass anisotropy, plays a major role for the interpretation of the observed signals.…