Time-Resolved X-ray Microscopy of Spin-Torque-Induced Magnetic Vortex Gyration

TL;DR

This study uses time-resolved X-ray microscopy to visualize how high-density alternating currents induce vortex gyration in ferromagnetic structures, revealing the roles of spin-transfer torque and Oersted fields.

Contribution

It provides the first detailed imaging of spin-torque-induced vortex dynamics with phase comparison to models, highlighting the combined effects of spin-transfer torque and Oersted fields.

Findings

Spin-torque accounts for about 70% of vortex excitation.

The phases of vortex gyration depend on chirality and current phase.

The results inform magnetic storage device design.

Abstract

Time-resolved X-ray microscopy is used to image the influence of alternating high-density currents on the magnetization dynamics of ferromagnetic vortices. Spin-torque induced vortex gyration is observed in micrometer-sized permalloy squares. The phases of the gyration in structures with different chirality are compared to an analytical model and micromagnetic simulations, considering both alternating spinpolarized currents and the current's Oersted field. In our case the driving force due to spin-transfer torque is about 70% of the total excitation while the remainder originates from the current's Oersted field. This finding has implications to magnetic storage devices using spin-torque driven magnetization switching and domain-wall motion.