DYNAMICS OF CURRENT-INDUCED SWITCHING IN SPIN-ORBIT TORQUE MAGNETIC DEVICES

Abstract

Spin-orbit torques in heavy metal/ferromagnet bilayers are expected to overcome spin-transfer torques for application to magnetic memories, in terms of power-efficiency, endurance and speed. However, switching nanomagnets by spin-orbit torques is hindered by a limited understanding of the switching dynamics as well as by the requirement that an external assist field must be applied to the systems to ensure deterministic switching. This thesis addresses these two emergent issues of spin-orbit-torque induced dynamics. The non-linear behaviour of the magnetization under a combination of the different spin-orbit torques is first analysed and reveals a regime of dynamic switching that does not require any external assist field. This study is then extended to the thermal regime where the switching requirements and the roles of the different torques are investigated using the Lagrangian field theory. Finally, switching is analysed in triaxial anisotropy devices where the additional shape anisotropy of ellipses can advantageously replace the assist field for deterministic spin-orbit torque switching. These simple and efficient switching schemes may greatly contribute to the realization of spin-orbit-torque-based memories.