UC Berkeley

This dissertation presents a systematic study on spin-orbit torque generation and manipulation in all oxide model systems consisting of ferromagnet La0.7Sr0.3MnO3, SrRuO3, multiferroic BiFeO3 and spin-orbit coupled SrIrO3. Efficient spin-orbit torque generation is crucial in the field of spintronics for the applications of spintronics-based memory and logic devices that requires the writing of magnetic states (i.e., switching the magnetization orientations). The development in efficient spin-orbit torque generation is staggered by the scarce of material candidates and the lack of extra degrees of freedom for spin current manipulation. The primary aim of this dissertation is to demonstrate how complex oxides can be utilized to generate spin currents efficiently and provide a viable pathway to control spin currents. In this dissertation, I will identify a complex oxide model system for spin current generation, with specific interest to investigate and understand the influence of electronic interaction enabled by the epitaxial interface on the spin-orbit torque generation. I will demonstrate that an epitaxial interface is able to facilitate spin current transmission and enable electronic interaction in the heterostructure; and the heterostructure interface, which is overlooked in the field of spintronics, is of vital importance for enhancing spin-orbit torque efficiency. Furthermore, the capability of BiFeO3 of transmitting spin current via antiferromagnet magnons is demonstrated with various techniques. Two pathways-modifying interface termination and using electric fields to control the ferroelectric polarization in BiFeO3, which in turn changes the spin current transmission, are demonstrated. Strikingly, bistable high/low spin transmission states are observed when reversing the ferroelectric polarization of BiFeO3, suggesting a coupling between spin propagation and ferroelectric polarization. In summary, the work presented in this dissertation reveals the important role that epitaxial interface plays in spin-orbit torque generation and demonstrates that multiferroic BiFeO3 is a good candidate for spin current transmission and manipulation. Additionally, the ferroelectric polarization controllable spin propagation in multiferroics offers an alternative to realize spintronics-based memory devices and the introduction of multiferroic materials to the field of spintronics opens up a new avenue for electrical control of spin currents.