Understanding spin-orbit torques in magnetic nanostructures

Spin-orbit torque allows electrical manipulation of magnetisation direction which has applications in future magnetic data-storage, and spintronic digital memory and information processing applications. It arises at the interface between a ferromagnet an non-magnetic heavy metal due to the spin-orbit interaction; this is thought to occur via two mechanisms - the spin-Hall effect due to spin-orbit scattering in the non-magnetic metal and the Rashba effect due to the breaking of structural inversion symmetry at the interface. The relative roles of these effects, and whether these are actually the primary cause of spin-orbit torques, remains unclear. Additionally, theoretical descriptions of spin-orbit torques neglect many factors that may be crucial - particularly the atomic scale crystal structure of the materials used and how this is impacted upon by the presence of an interface, and the possibility of proximity induced magnetism in the non-magnetic layer creating an equilibrium spin imbalance. These factors will be investigated by making devices from designed high-quality thin-film multilayer structures by lithographic microfabrication, and studying spin-orbit torques using a combination of laboratory-based magneto-electrical, magneto-optical, and microstructural measurements in conjunction with facilities-based work using polarised neutron and resonant x-ray scattering techniques.