Damping's effect on the magnetodynamics of spin Hall nano-oscillators

TL;DR

This study investigates how varying spin wave damping affects the auto-oscillation behavior of spin Hall nano-oscillators, revealing that damping influences threshold current, mode profile, and linewidth in different magnetic field regimes.

Contribution

It provides systematic experimental analysis of damping effects on SHNO magnetodynamics, highlighting the relationship between damping, threshold current, and linewidth.

Findings

Threshold current scales with damping.

Auto-oscillation mode profile evolves with field.

Lower linewidth observed in high-damping materials at low fields.

Abstract

We study the impact of spin wave damping ($\alpha$) on the auto-oscillation properties of nano-constriction based spin Hall nano-oscillators (SHNOs). The SHNOs are based on a 5 nm Pt layer interfaced to a 5 nm Py$_{100-x-y}$Pt$_{x}$Ag$_{y}$ magnetic layer, where the Pt and Ag contents are co-varied to keep the saturation magnetization constant (within 10 %), while $\alpha$ varies close to a factor of three. We systematically investigate the influence of the Gilbert damping on the magnetodynamics of these SHNOs by means of electrical microwave measurements. Under the condition of a constant field, the threshold current scales with the damping in the magnetic layer. The threshold current as a function of field shows a parabolic-like behavior, which we attribute to the evolution of the spatial profile of the auto-oscillation mode. The signal linewidth is smaller for the high-damping materials in low magnetic fields, although the lowest observed linewidth was measured for the alloy with least damping.