Nonmonotonic inelastic tunneling spectra due to surface spin excitations in ferromagnetic junctions

TL;DR

This paper explains the bias-voltage dependence of inelastic tunneling spectra in ferromagnetic junctions through electron-magnon interaction matrix elements, using nonequilibrium Green's function calculations within an itinerant-electron model.

Contribution

It introduces a model where bias-voltage dependence arises from tunneling matrix elements derived from Coulomb exchange, advancing understanding of inelastic tunneling spectra.

Findings

Bias-voltage dependence explained by tunneling matrix elements.

Calculated spectra match experimental bias dependence.

Model applies to both parallel and antiparallel magnetizations.

Abstract

The paper addresses inelastic spin-flip tunneling accompanied by surface spin excitations (magnons) in ferromagnetic junctions. The inelastic tunneling current is proportional to the magnon density of states which is energy-independent for the surface waves and, for this reason, cannot account for the bias-voltage dependence of the observed inelastic tunneling spectra. This paper shows that the bias-voltage dependence of the tunneling spectra can arise from the tunneling matrix elements of the electron-magnon interaction. These matrix elements are derived from the Coulomb exchange interaction using the itinerant-electron model of magnon-assisted tunneling. The results for the inelastic tunneling spectra, based on the nonequilibrium Green's function calculations, are presented for both parallel and antiparallel magnetizations in the ferromagnetic leads.