Direct observation of magnetization dynamics generated by nano-contact spin-torque vortex oscillators

TL;DR

This study uses time-resolved Kerr microscopy to directly visualize magnetization dynamics in nano-contact spin-torque vortex oscillators, revealing insights into phase-locking behavior and dynamics outside electrical detection.

Contribution

It provides the first direct imaging of magnetization dynamics in NC-STVOs during phase-locking, including partial locking states and interactions between multiple contacts.

Findings

Magnetization dynamics extend outside the nano-contact footprint.

Partial locking involves periodic core trajectory changes.

Multiple NCs show enhanced amplitude and reduced linewidth.

Abstract

Time-resolved scanning Kerr microscopy has been used to directly image the magnetization dynamics of nano-contact (NC) spin-torque vortex oscillators (STVOs) when phase-locked to an injected microwave (RF) current. The Kerr images reveal free layer magnetization dynamics that extend outside the NC footprint, where they cannot be detected electrically, but which are crucial to phase-lock STVOs that share common magnetic layers. For a single NC, dynamics were observed not only when the STVO frequency was fully locked to that of the RF current, but also for a partially locked state characterized by periodic changes in the core trajectory at the RF frequency. For a pair of NCs, images reveal the spatial character of dynamics that electrical measurements show to have enhanced amplitude and reduced linewidth. Insight gained from these images may improve understanding of the conditions required for mutual phase-locking of multiple STVOs, and hence enhanced microwave power emission.