Bipolar High Field Excitations in Co/Cu/Co Nanopillars

TL;DR

This study investigates current-induced magnetic excitations in Co/Cu/Co nanopillars at low temperatures, revealing bipolar excitations at high current densities likely caused by spin-wave instabilities due to asymmetrical spin accumulation.

Contribution

It introduces a new explanation for bipolar excitations in bilayer nanopillars, attributing them to transverse spin-wave instabilities caused by asymmetric spin accumulation.

Findings

Bipolar excitations observed at high current densities.

Excitations lead to decreased differential resistance.

Proposed mechanism involves spin-wave instabilities due to asymmetry.

Abstract

Current-induced magnetic excitations in Co/Cu/Co bilayer nanopillars ($\sim$50 nm in diameter) have been studied experimentally at low temperatures for large applied fields perpendicular to the layers. At sufficiently high current densities excitations, which lead to a decrease in differential resistance, are observed for both current polarities. Such bipolar excitations are not expected in a single domain model of spin-transfer. We propose that at high current densities strong asymmetries in the longitudinal spin accumulation cause spin-wave instabilities transverse to the current direction in bilayer samples, similar to those we have reported for single magnetic layer junctions.