Large spin Hall conductivity in Pt as measured with non-contact microwave spectroscopy

By use of microwave spectroscopy, we have measured the spin Hall effect (SHE) and spin transparency in bilayers of Ni80Fe20/Pt. The method uses a phase-sensitive amplitude analysis of FMR spectra with unpatterned thin films that are proximate to, but not electrically connected with a coplanar waveguide [1]. Both SHE and iSHE are measured simultaneously, as mandated by Onsager reciprocity. The method does not require the samples to have an easy axis, nor knowledge of the precession angle. Damping is simultaneously measured, permitting self-consistent fitting of the SHE and spin pumping signals [2]. In agreement with previous reports [3], the spin transport efficiency between Ni80Fe20 and Pt is << 1, presumably due to interfacial spin memory loss. Also, the transparency is a strong function of deposition order, with a 3x reduction when Ni80Fe20 is grown on Pt. While the effective SHE signal and spin diffusion length are comparable to previous reports [4], substantial spin memory loss implies a larger value for the intrinsic SHE ratio of Pt (~ 0.4) than previously reported. [1] Berger, A. J., et al. (2018). PRB 97 094407. [2] Berger, A. J., et al. (2018). PRB 98 024402. [3] Rojas-Sánchez, J.-C., et al. (2014). PRL 112 106602. [4] Nguyen, M.-H., et al. (2016). PRL 116 126601