Microscopic theory of the Coulomb based exchange coupling in magnetic tunnel junctions

TL;DR

This paper introduces a Coulomb interaction-based theory for interlayer exchange coupling in magnetic tunnel junctions, highlighting its dependence on dielectric properties and electric fields, and comparing it with traditional hopping mechanisms.

Contribution

It presents a novel Coulomb interaction-based model for IEC in MTJs, emphasizing its dependence on dielectric properties and electric fields, and its potential to surpass hopping-based coupling.

Findings

Coulomb-based IEC can exceed hopping-based exchange coupling.

IEC strongly depends on the dielectric constant of the insulating layer.

IEC varies significantly with temperature and electric field, especially near ferroelectric phase transitions.

Abstract

We study interlayer exchange coupling (IEC) based on the many-body Coulomb interaction between conduction electrons in magnetic tunnel junction (MTJ). This mechanism complements the known IEC based on virtual electron hopping (or spin currents). We find that these two mechanisms have different behavior on system parameters. The Coulomb based IEC may exceed the hopping based exchange coupling. We show that the Coulomb based exchange coupling, in contrast to the hopping based coupling, depends strongly on the dielectric constant of the insulating layer. The dependence of the IEC on the dielectric properties of the insulating layer in MTJ is similar to magneto-electric (ME) effect where electric and magnetic degrees of freedom are coupled. We calculate the IEC as a function of temperature and electric field for MTJ with ferroelectric (FE) layer and show that IEC has a sharp decrease in the vicinity of the FE phase transition and varies strongly with external electric field.