Temperature Dependence of Spin Pumping in Ni81Fe19/NbN Bilayer Thin Films

TL;DR

This study explores how temperature influences spin pumping and inverse spin Hall effect in Ni81Fe19/NbN bilayers, revealing temperature-dependent changes in spin Hall angle and voltage, especially near the superconducting transition.

Contribution

It provides the first detailed analysis of temperature effects on spin pumping and inverse spin Hall effect in Ni81Fe19/NbN bilayers over broad frequency and temperature ranges.

Findings

Spin Hall angle increases with temperature, exceeding previous reports.

Inverse spin Hall effect voltage decreases significantly below Tc.

FMR linewidth broadens as temperature drops below Tc.

Abstract

We present a comprehensive study of broadband spin pumping utilizing the inverse spin Hall effect phenomena in bilayer samples comprising Ni81Fe19 (15 nm) and NbN (with NbN thickness varying from 20 nm to 140 nm), conducted over a temperature and frequency range spanning from 300 K to 4 K and 2 GHz to 12 GHz, respectively. Our investigations reveal a systematic shift in ferromagnetic resonance fields, amplitude, and line widths as functions of both frequency and temperature. Notably, we observed a temperature-dependent increase in the spin Hall angle value, surpassing previously reported values. Furthermore, our results demonstrate a pronounced temperature dependence in the inverse spin Hall effect voltage, exhibiting a significant reduction below the Tc. This reduction in inverse spin Hall effect voltage is accompanied by an increase in the linewidth of the ferromagnetic resonance mode.