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 \{ 0.3,0.75\} $, detected via the ferromagnetic resonance of a permalloy (Py = Ni$_{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 ${\theta _{{\text{SH}}}} \approx 1$, spin diffusion length ${\lambda _{\text{s}}}$, spin mixing conductance $G_{ \uparrow \downarrow }^{}$, and damping due to spin memory loss ${\alpha _{{\text{SML}}}}$. We compare our results with similar experiments on Py/Pt bilayers measured using the same method.