Excitation of self-localized spin-wave "bullets" by spin-polarized current in in-plane magnetized magnetic nano-contacts: a micromagnetic study

TL;DR

This micromagnetic study reveals that in-plane magnetized nano-contacts can support a nonlinear, self-localized spin wave 'bullet' mode with lower excitation thresholds and hysteretic switching, expanding understanding of spin wave dynamics.

Contribution

It demonstrates the existence and properties of a nonlinear spin wave 'bullet' mode in nano-contacts, highlighting its lower threshold and localized nature compared to linear modes.

Findings

The 'bullet' mode exists over a wider current range.

The 'bullet' mode frequency is below linear spin wave spectrum.

Hysteretic switching occurs between modes when current varies.

Abstract

It was shown by micromagnetic simulation that a current-driven in-plane magnetized magnetic nano-contact, besides a quasi-linear propagating ("Slonczewski") spin wave mode, can also support a nonlinear self-localized spin wave "bullet" mode that exists in a much wider range of bias currents. The frequency of the "bullet" mode lies below the spectrum of linear propagating spin waves, which makes this mode evanescent and determines its spatial localization. The threshold current for the excitation of the self-localized "bullet" is substantially lower than for the linear propagating mode, but finite-amplitude initial perturbations of magnetization are necessary to generate a "bullet" in our numerical simulations, where thermal fluctuations are neglected. Consequently, in these simulations the hysteretic switching between the propagating and localized spin wave modes is found when the bias current is varied.