Near-Unity Spin Hall Ratio in Ni$_x$Cu$_{1-x}$ Alloys

Abstract: We report a large spin Hall effect in the 3$d$ transition metal alloy Ni$x$Cu${1-x}$ for $x\in\left{ 0.3,0.75\right} $, detected via the ferromagnetic resonance of a Permalloy (Py = Ni${80}$Fe${20}$) film deposited in a bilayer with the alloy. A thickness series at $x$ = 0.6, for which the alloy is paramagnetic at room temperature, allows us to determine the spin Hall ratio $\theta_{\rm{SH}}\approx1$, spin diffusion length $\lambda_{\rm{s}}$, spin mixing conductance $G_{\uparrow\downarrow}$, and damping $\alpha_{\rm{SML}}$ due to spin memory loss . We compare our results with similar experiments on Py/Pt bilayers measured using the same method. Ab initio band structure calculations with disorder and spin-orbit coupling suggest an intrinsic spin Hall effect in Ni$x$Cu${1-x}$ alloys, although the experiments here cannot distinguish between extrinsic and intrinsic mechanisms.