Micro-focused Brillouin light scattering study of the magnetization dynamics driven by Spin Hall effect in a transversely magnetized NiFe nanowire

TL;DR

This study uses micro-focused Brillouin light scattering to analyze how spin currents generated by the spin-Hall effect amplify and modify magnetization dynamics in a transversely magnetized NiFe nanowire, revealing threshold behaviors and mode interactions.

Contribution

It provides new insights into the non-linear spin wave dynamics driven by the spin-Hall effect in nanowires, supported by experimental measurements and micromagnetic simulations.

Findings

Frequency redshift of spin wave modes with increasing current

Enhanced mode cross section at higher current

Emergence of an additional localized mode above threshold

Abstract

We employed micro-focused Brillouin light scattering to study the amplification of the thermal spin wave eigenmodes by means of a pure spin current, generated by the spin-Hall effect, in a transversely magnetized Pt(4nm)/NiFe(4nm)/SiO2(5nm) layered nanowire with lateral dimensions 500x2750 nm2. The frequency and the cross section of both the center (fundamental) and the edge spin wave modes have been measured as a function of the intensity of the injected dc electric current. The frequency of both modes exhibits a clear redshift while their cross section is greatly enhanced on increasing the intensity of the injected dc. A threshold-like behavior is observed for a value of the injected dc of 2.8 mA. Interestingly an additional mode, localized in the central part of the nanowire, appears at higher frequency on increasing the intensity of the injected dc above the threshold value. Micromagnetic simulations were used to quantitatively reproduce the experimental results and to investigate the complex non-linear dynamics induced by the spin-Hall effect, including the modification of the spatial profile of the spin wave modes and the appearance of the extra mode above the threshold.