Efficient spin-orbit torque in magnetic trilayers using all three polarizations of a spin current

Abstract

Spin-orbit coupling can convert a charge current into a spin current, thereby generating a spin-orbit torque (SOT). Energy-efficient, commercially viable SOT technology requires field-free switching of perpendicular magnetization at low current. In heterostructures incorporating ferromagnets, the polarization of spin current consists, in general, of three vectors: ((z) over cap x (E) over cap), (m) over cap and (m) over cap x ((z) over cap x (E) over cap), where (z) over cap is the film normal, E is the electric-field direction and in is the magnetization direction. Previous studies on SOT have used only part of all the three polarizations, because the two in-dependent polarizations are mutually orthogonal. Here we show that all the three polarizations can be exploited in systems with ferromagnet/non-magnet/ferromagnet trilayers, having a bottom epitaxial ferromagnet layer with a tilted magnetic easy axis. The approach reduces the field-free SOT switching current compared with approaches that exploit only part of all the three polarizations. We also show that this technique can be used with a sputtered polycrystalline trilayer, illustrating its potential applicability to mass production.