Strong Enhancement Of The Spin Hall Effect By Spin Fluctuations Near The Curie Point Of Fe_xPt_1-x Alloys

Robust spin Hall effects (SHE) in non-magnetic heavy metal systems are either attributed to an intrinsic band-structure effect or to extrinsic spin-dependent scattering from impurities, namely side-jump or skew scattering. Here we will report on extraordinarily strong skew scattering, attributable to spin fluctuations, in ferromagnetic Fe_xPt_1-x alloys near their Curie point, tunable with x. This results in a damping-like spin-orbit torque being exerted on an adjacent ferromagnetic layer that is strongly temperature dependent in this transition region, with a peak value that indicates a lower bound 0.34 ± 0.02 for the peak spin Hall ratio within the FePt. We also observe a pronounced peak in the effective spin-mixing conductance of the FM/FePt interface, and determine the spin diffusion length in these Fe_xPt_1-x alloys. These results establish new opportunities for fundamental studies of spin dynamics and transport in ferromagnetic systems with strong spin fluctuations, and a new pathway for efficiently generating strong spin currents for applications.