Intermediate state switching dynamics in magnetic double layer nanopillars grown by molecular beam epitaxy

TL;DR

This paper reports the discovery of a stable intermediate resistance state in Co/Cu/Co nanopillars, influenced by an additional magnetic easy axis, with implications for spin transfer torque switching and magnetic excitations.

Contribution

It introduces a novel intermediate resistance state in magnetic nanopillars grown by molecular beam epitaxy, linked to an extra in-plane magnetic easy axis.

Findings

Existence of a stable intermediate resistance state.

Observation of broad microwave emission spectrum.

Suppression of coherent large-angle precession due to the additional easy axis.

Abstract

We observe a stable intermediate resistance switching state in the current perpendicular to plane geometry for all Co/Cu/Co double layer nanopillar junctions grown by molecular beam epitaxy. This novel state has a resistance between the resistances of the parallel and antiparallel alignment of both Co-layer magnetizations. The state, which originates from an additional in-plane magnetic easy axis, can be reached by spin transfer torque switching or by an external magnetic field. In addition to spin torque-induced coherent small-angle spin wave modes we observe a broad microwave emission spectrum. The latter is attributed to incoherent magnetic excitations that lead to a switching between the intermediate state and the parallel or antiparallel alignment of both ferromagnetic layers. We conclude that the additional magnetic easy axis suppresses a stable trajectory of coherent large-angle precession, which is not observed in our samples.