Current direction dependent spin Hall magnetoresistance in epitaxial Pt/Co bilayers on MgO(110)

Abstract

We demonstrate that the spin Hall magnetoresistance (SMR) of epitaxial Pt/Co bilayers on MgO(110) single crystal substrates is strongly anisotropic and depends on the applied current direction with respect to the two primary in-plane crystal directions [001] and $[1\overline{1}0]$, in the Pt layer. SMR results at different temperatures qualitatively suggest the D'yakonov-Perel spin relaxation mechanism through the invariance of the spin diffusion length ${\ensuremath{\lambda}}_{sf}$ for a given current direction, while also suggesting an anisotropic Rashba-Edelstein effect from the ratio of ${\ensuremath{\lambda}}_{sf}^{[001]}$ to ${\ensuremath{\lambda}}_{sf}^{[1\overline{1}0]}$. Finally, deviation from the standard SMR model spurs the need for new theory that properly characterizes and quantifies the anisotropies in such epitaxial systems.