Magnetic Droplet Soliton Nucleation in Oblique Fields

TL;DR

This study investigates how the nucleation of magnetic droplets and spin-wave dynamics in spin torque nano-oscillators depend on the out-of-plane magnetic field angle, revealing the influence of magnetic anisotropy and nonlinear effects.

Contribution

It demonstrates the angle-dependent transition from droplet nucleation to propagating spin waves and highlights the role of perpendicular magnetic anisotropy in these dynamics.

Findings

Droplet nucleation occurs at angles down to ~50 degrees.

Below 50 degrees, propagating spin waves dominate.

Perpendicular magnetic anisotropy reverses the angular dependence of spin-wave nonlinearity.

Abstract

We study the auto-oscillating magnetodynamics in orthogonal spin torque nano-oscillators (STNOs) as a function of the out-of-plane (OOP) magnetic field angle. In perpendicular fields and at OOP field angles down to approximately 50 degrees we observe the nucleation of a droplet. However, for field angles below 50 degrees, experiments indicate that the droplet gives way to propagating spin waves, in agreement with our micromagnetic simulations. Theoretical calculations show that the physical mechanism behind these observations is the sign changing of spin-wave nonlinearity (SWN) by angle. In addition, we show that the presence of a strong perpendicular magnetic anisotropy (PMA) free layer in the system reverses the angular dependence of the SWN and dynamics in STNOs with respect to the known behavior determined for the in-plane magnetic anisotropy free layer. Our results are of fundamental interest in understanding the rich dynamics of nanoscale solitons and spin-wave dynamics in STNOs.