Bangguo Xiong, UT-Austin

"Toward a Geometric Theory of Magnetization Dynamics: Electronic Contribution in the Semiclassical Approach"

Abstract: This dissertation presents theoretical studies of the magnetization dynamics in the presence of electric field in ferromagnetic materials. Our results provide methods for the field control of the magnetization status for both domain and domain walls of magnetic structures. We have developed a semiclassical theory for the magnetization implicitly coupled to electronic degrees of freedom. Static electric fields modify the magnetization dynamics as first-order perturbations, with which we were able to give a physically clear interpretation of the current-induced spin-orbit torques.

For inhomogeneous magnetic materials, the electronic spin dipole influences the magnetization dynamics in terms of Dzyaloshinskii-Mariya interaction. We obtained the field-induced spin dipole and discusses the non-equilibrium Dzyaloshinskii-Mariya interaction. In addition, the induced effective fields have a geometric contribution in terms of the Chern forms, providing driven force for the magnetization dynamics.

We used toy models mimicking a ferromagnet-topological-insulator interface to illustrate the various effects.