Effect of dynamical electron correlations on the tunnelling magnetoresistance of Fe/MgO/Fe(001) junctions

TL;DR

This study uses advanced theoretical methods to show how dynamical electron correlations affect the transport and tunneling magnetoresistance in Fe/MgO/Fe magnetic tunnel junctions, especially under finite bias conditions.

Contribution

It introduces a combined DFT+DMFT approach with a rigid shift approximation to efficiently analyze bias-dependent transport properties in MTJs, highlighting the role of electron correlations.

Findings

Dynamical correlations reduce spin splitting of Fe 3d orbitals.

Correlation effects are more pronounced in the antiparallel configuration.

DMFT predicts a lower bias threshold for TMR suppression, aligning better with experiments.

Abstract

We employ dynamical mean-field theory (DMFT) combined with density functional theory (DFT) and the non-equilibrium Green's function technique to investigate the steady-state transport properties of an Fe/MgO/Fe magnetic tunnel junction (MTJ), focusing on the impact of dynamical electron correlations on the Fe $3d$ orbitals. By applying the rigid shift approximation, we extend the calculations from zero- to finite-bias in a simple and computationally efficient manner, obtaining the bias-dependent electronic structure and current-versus-voltage characteristic curve in both the parallel and antiparallel configurations. In particular, we find that dynamical electron correlation manifests as a reduction in the spin splitting of the Fe $3d_{z^2}$ state compared to DFT predictions and introduces a finite relaxation time. The impact of these effects on the transport properties, however, varies significantly between magnetic configurations. In the parallel configuration, the characteristic curves obtained with DFT and DMFT are similar, as the transport is mostly due to the coherent transmission of spin-up electrons through the MgO barrier. Conversely, in the antiparallel configuration, correlation effects become more significant, with DMFT predicting a sharp current increase due to bias-driven inelastic electron-electron scattering. As a consequence, DMFT gives a lower bias threshold for the suppression of the tunneling magnetoresistance ratio compared to DFT, matching experimental data more closely.