Near-unity spin Hall ratio in Ni _x Cu_1-x alloys

We report a large spin Hall effect in the 3d transition metal alloy Ni _x Cu_1-x for x ∈ {0.3, 0.75}, detected via the ferromagnetic resonance of a permalloy (Py = Ni₈₀Fe₂₀) 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 θ _SH ≈ 1, spin diffusion length λ_s, spin mixing conductance G _⇅, and damping due to spin memory loss α_SML. 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.