Spin-transfer-induced excitations in bilayer magnetic nanopillars at high fields: The effects of contact layers

TL;DR

This study investigates how contact layers influence high-field spin-transfer excitations in bilayer magnetic nanopillars, revealing that certain excitations depend on the contact configuration, confirming theoretical predictions.

Contribution

It demonstrates the critical role of contact layers in enabling high-field spin-wave excitations in bilayer nanopillars, providing experimental validation of recent theoretical models.

Findings

High-field bipolar excitations occur only in samples with specific contact layers.

Contact layers significantly affect spin-current-induced phenomena.

Experimental results confirm recent theoretical predictions on spin-wave excitations.

Abstract

Current-induced excitations in bilayer magnetic nanopillars have been studied with large magnetic fields applied perpendicular to the layers at low temperature. Junctions investigated all have Cu/Co/Cu/Co/Cu as core layer stacks. Two types of such junctions are compared, one with the core stack sandwiched between Pt layers (type A), the other with Pt only on one side of the stack (type B). Transport measurements show that these two types of junctions have similar magnetoresistance and slope of critical current with respect to field, while A samples have higher resistance. The high-field bipolar excitation, as was previously reported [Oezyilmaz et al., Phys. Rev. B 71, 140403(R) (2005)], is present in B samples only. This illustrates the importance of contact layers to spin-current-induced phenomena. This also confirms a recent prediction on such spin-wave excitations in bilayers.