Spectral Characteristics of the Microwave Emission by the Spin Hall Nano-Oscillator

TL;DR

This study uses microwave spectroscopy to analyze magnetization oscillations in a Permalloy film induced by spin Hall effect-generated spin currents, revealing self-localized spin-wave solitons with temperature-dependent spectral properties.

Contribution

It provides new insights into the spectral behavior of spin Hall nano-oscillators and compares their characteristics to traditional spin-torque nano-oscillators at various temperatures.

Findings

Oscillation frequency is below ferromagnetic resonance, indicating self-localized spin-wave solitons.

Spectral characteristics are similar to spin-torque nano-oscillators at cryogenic temperatures.

Linewidth increases exponentially with temperature, and a secondary spectral peak appears.

Abstract

We utilized microwave spectroscopy to study the magnetization oscillations locally induced in a Permalloy film by a pure spin current, which is generated due to the spin Hall effect in an adjacent Pt layer. The oscillation frequency is lower than the ferromagnetic resonance of Permalloy, indicating that the oscillation forms a self-localized nonpropagating spin-wave soliton. At cryogenic temperatures, the spectral characteristics are remarkably similar to the traditional spin-torque nano-oscillators driven by spin-polarized currents. However, the linewidth of the oscillation increases exponentially with temperature and an additional peak appears in the spectrum below the ferromagnetic resonance, suggesting that the spectral characteristics are determined by interplay between two localized dynamical states.