Nanocontact vortex oscillators based on Co$_2$MnGe pseudo-spin valves

TL;DR

This paper experimentally investigates vortex dynamics in Co$_2$MnGe-based nanocontact spin valves, revealing various spin-transfer induced vortex modes and their complex behaviors, advancing understanding of magnetic vortex oscillators.

Contribution

It demonstrates the fabrication and analysis of vortex oscillators using Co$_2$MnGe pseudo-spin valves, highlighting new dynamic modes and their interactions in nanoscale devices.

Findings

Observation of self-sustained vortex gyration above a current threshold

Identification of multiple vortex dynamic modes including hopping and coexistence

Demonstration of complex mode behaviors in spin-transfer vortex oscillators

Abstract

We present an experimental study of vortex dynamics in magnetic nanocontacts based on pseudo spin valves comprising the Co$_2$MnGe Heusler compound. The films were grown by molecular beam epitaxy, where precise stoichiometry control and tailored stacking order allowed us to define the bottom ferromagnetic layer as the reference layer, with minimal coupling between the free and reference layers. 20-nm diameter nanocontacts were fabricated using a nano-indentation technique, leading to self-sustained gyration of the vortex generated by spin-transfer torques above a certain current threshold. By combining frequency- and time-domain measurements, we show that different types of spin-transfer induced dynamics related to different modes associated to the magnetic vortex configuration can be observed, such as mode hopping, mode coexistence and mode extinction appear in addition to the usual gyration mode.