Spin-current mediated exchange coupling in MgO-based magnetic tunnel junctions

TL;DR

This study demonstrates the existence of spin-current mediated exchange coupling in MgO-based magnetic tunnel junctions through layer-resolved ferromagnetic resonance and theoretical modeling.

Contribution

It provides the first clear experimental and theoretical evidence of spin pumping-mediated interlayer coupling in MgO-based magnetic tunnel junctions.

Findings

Strong interlayer interaction observed via ferromagnetic resonance

Theoretical model confirms spin pumping as the coupling mechanism

Statistical analysis unambiguously proves spin-current mediation

Abstract

Heterostructures composed of ferromagnetic layers that are mutually interacting through a nonmagnetic spacer are at the core of magnetic sensor and memory devices. In the present study, layer-resolved ferromagnetic resonance was used to investigate the coupling between the magnetic layers of a Co/MgO/Permalloy magnetic tunnel junction. Two magnetic resonance peaks were observed for both magnetic layers, as probed at the Co and Ni L3 x-ray absorption edges, showing a strong interlayer interaction through the insulating MgO barrier. A theoretical model based on the Landau-Lifshitz-Gilbert-Slonczewski equation was developed, including exchange coupling and spin pumping between the magnetic layers. Fits to the experimental data were carried out, both with and without a spin pumping term, and the goodness of the fit was compared using a likelihood ratio test. This rigorous statistical approach provides an unambiguous proof of the existence of interlayer coupling mediated by spin pumping.