Strain-induced enhancement of the Seebeck effect in magnetic tunneling junctions via interface resonant tunneling: Ab-initio study

TL;DR

This study demonstrates that applying tetragonal distortion and optimizing barrier thickness in Fe/MgO/Fe magnetic tunnel junctions significantly enhances their thermoelectric properties, especially the Seebeck coefficient, through interface resonant tunneling.

Contribution

It provides a first-principles analysis showing how strain and barrier thickness control can optimize thermoelectric performance in magnetic tunnel junctions.

Findings

Seebeck coefficient depends on barrier thickness and tetragonal distortion.

Compressive tetragonal distortion enhances the Seebeck coefficient via interface resonant states.

Resonant tunneling increases the power factor under compressive strain.

Abstract

We investigate the thermoelectric properties of Fe/MgO/Fe(001) magnetic tunnel junctions (MTJs) by means of the linear-response theory combined with a first-principles-based Landauer-B\"uttiker approach. We find that the Seebeck coefficient of Fe/MgO/Fe(001) MTJs strongly depends on the barrier thickness and the tetragonal distortion. A compressive tetragonal distortion of the in-plane lattice parameter in the MTJs provides interface resonant states just above the Fermi energy. This causes resonant tunneling in the MTJs and significantly enhances the Seebeck coefficient when the thickness of the MgO barrier is around 1 nm (four or five atomic layers of MgO). Moreover, an extensive tetragonal distortion of the in-plane lattice parameter pushes the interface states away from the Fermi energy, leading to a reduction of the Seebeck coefficient. Furthermore, we find that the interface resonant tunneling enhances the power factor of the MTJs for the compressive distortion. These results indicate that control of the barrier thickness and the tetragonal distortion will be effective for maximizing the thermoelectric properties of MTJs.