Interface-driven spin-orbit torques in magnetic heterostructures

Abstract

The connection between charge and spin transport in solid state materials offers new techniques for generating and detecting spin currents and could potentially allow high-performance memory and logic devices. Simple multilayer thin films or "heterostructures" such as Pt/Co have broken inversion symmetry, so a charge current gives rise to net spin current. Electrical and optical measurements reveal the effect of spin current on the magnetization, including chiral spin textures such as domain walls (DWs) and skyrmions. The magnetic properties of an ultrathin magnetic film are strongly sensitive to interfacial effects such as interfacial anisotropy and the Dzyaloshinskii-Moriya Interaction (DMI), which stabilizes chiral spin textures. This thesis is motivated to systematically vary the layer structure of magnetic heterostructures to understand and quantify spin-orbit torques. I showed that switching efficiency is consistent with harmonic spin orbit torque measurements in Pt/Co/Ta. My automation software and improved electromagnet enabled a new experimental technique that highlights the role of DMI in spin-orbit torque switching. I showed that a gold spacer layer inserted between platinum and cobalt independently modulates the DMI and spin transport. I demonstrated SOT switching of a ferromagnetic insulator for the first time. I also developed a temperature-controlled, high-speed electrical and optical measuring system to observe record-breaking DW velocity in ferrimagnetic GdCo. This thesis focuses on building experimental apparatus and understanding spin-orbit torques.