We quantify the spin Hall angle ${\theta }_{\mathrm{SH}}$ and spin-diffusion length $l_{\mathrm{sd}}$ of $\mathrm{Nb}$ from inverse spin Hall effect (ISHE) measurements in $\mathrm{Nb}/{\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ bilayers under ferromagnetic resonance. By varying the $\mathrm{Nb}$ thickness $t_{\mathrm{Nb}}$ and comparing to a ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}/\mathrm{Pt}$ reference sample, room temperature values of ${\theta }_{\mathrm{SH}}$ and $l_{\mathrm{sd}}$ for $\mathrm{Nb}$ are estimated to be approximately −0.001 and 30 nm, respectively. We also investigate the ISHE as a function of temperature T for different $t_{\mathrm{Nb}}$. Above the superconducting transition temperature $T_c$ of $\mathrm{Nb}$ , a clear $t_{\mathrm{Nb}}$-dependent T evolution of the ISHE is observed whereas below $T_c$, the ISHE voltage drops rapidly and is below the sensitivity of our measurement setup at a lower T. This suggests the strong decay of the quasiparticle (QP) charge-imbalance relaxation length across $T_c$, as supported by an additional investigation of the ISHE in a different sample geometry along with model calculation. Our finding suggests careful consideration should be made when developing superconductor spin Hall devices that intend to utilize QP-mediated spin-to-charge interconversion.

• Received 26 March 2018
• Revised 28 May 2018

DOI:https://doi.org/10.1103/PhysRevApplied.10.014029