I-V curves of Fe/MgO (001) single- and double-barrier tunnel junctions

TL;DR

This study uses ab initio calculations to analyze the current-voltage behavior of Fe/MgO magnetic tunnel junctions, revealing enhanced magnetoresistance and resonant tunneling effects in double-barrier configurations.

Contribution

First ab initio study of I-V characteristics in Fe/MgO (001) tunnel junctions, highlighting differences between single- and double-barrier structures and identifying resonant tunneling phenomena.

Findings

Double-barrier junctions show larger magnetoresistance.

Magnetoresistance decays slower with bias in double barriers.

Resonant tunneling peak at 0.1 V in double barriers.

Abstract

In this work, we calculate with ab initio methods the current-voltage characteristics for ideal single- and double-barrier Fe/MgO (001) magnetic tunnel junctions. The current is calculated in the phase-coherent limit by using the recently developed SMEAGOL code, combining the nonequilibrium Green function formalism with density-functional theory. In general we find that double-barrier junctions display a larger magnetoresistance, which decays with bias at a slower pace than their single-barrier counterparts. This is explained in terms of enhanced spin filtering from the middle Fe layer sandwiched in between the two MgO barriers. In addition, for double-barrier tunnel junctions, we find a well defined peak in the magnetoresistance at a voltage of V=0.1 V. This is the signature of resonant tunneling across a majority quantum well state. Our findings are discussed in relation to recent experiments.