Spin orbit torque nano-oscillators by dipole field-localized spin wave modes

Abstract

We demonstrate a high-quality spin orbit torque nano-oscillator comprised of spin wave modes confined by the magnetic field by the strongly inhomogeneous dipole field of a nearby micromagnet. This approach enables variable spatial confinement and systematic tuning of magnon spectrum and spectral separations for studying the impact of multi-mode interactions on auto-oscillations. We find these dipole field-localized spin wave modes exhibit good characteristic properties as autooscillators-narrow linewidth and large amplitude-while persisting up to room temperature. We find that the linewidth of the lowest-lying localized mode is approximately proportional to temperature in good agreement with theoretical analysis of the impact of thermal fluctuations. This demonstration of a clean oscillator with tunable properties provides a powerful tool for understanding the fundamental limitations and linewidth contributions to improve future spin-Hall oscillators.

Origin of Nonlinear Damping due to Mode Coupling in Auto-Oscillatory Modes Strongly Driven by Spin-Orbit Torque

“…However, additional damping channels arise in extended thin film structures through nonlinear magnon scattering that prevents auto-oscillation [4]. These damping channels can be suppressed by restricting the area of the AO by fabricating a nano-constriction [3,10] as well as other methods of spatial mode confinement such as dimensional reduction [4] and local dipolar field [15][16][17].…”