A first-principles study of tunneling magnetoresistance in Fe/MgAl2O4/Fe(001) magnetic tunnel junctions

TL;DR

This study uses first-principles calculations to analyze spin-dependent transport in Fe/MgAl2O4/Fe(001) magnetic tunnel junctions, revealing factors affecting tunneling magnetoresistance ratios and the impact of band-folding effects.

Contribution

It provides a detailed first-principles analysis of the electronic structure and conductance in Fe/MgAl2O4/Fe(001) MTJs, highlighting the influence of band-folding on TMR ratios.

Findings

TMR ratio of Fe/MgAl2O4/Fe(001) MTJs is about 160%, much lower than Fe/MgO/Fe(001).

Evanescent delta 1 symmetry states suggest potential for high TMR.

Band-folding effects introduce conductive channels, reducing TMR.

Abstract

We investigated the spin-dependent transport properties of Fe/MgAl2O4/Fe(001) magnetic tunneling junctions (MTJs) on the basis of first-principles calculations of the electronic structures and the ballistic conductance. The calculated tunneling magnetoresistance (TMR) ratio of a Fe/MgAl2O4/Fe(001) MTJ was about 160%, which was much smaller than that of a Fe/MgO/Fe(001) MTJ (1600%) for the same barrier thickness. However, there was an evanescent state with delta 1 symmetry in the energy gap around the Fermi level of normal spinel MgAl2O4, indicating the possibility of a large TMR in Fe/MgAl2O4/Fe(001) MTJs. The small TMR ratio of the Fe/MgAl2O4/Fe(001) MTJ was due to new conductive channels in the minority spin states resulting from a band-folding effect in the two-dimensional (2-D) Brillouin zone of the in-plane wave vector (k//) of the Fe electrode. Since the in-plane cell size of MgAl2O4 is twice that of the primitive in-plane cell size of bcc Fe, the bands in the boundary edges are folded, and minority-spin states coupled with the delta 1 evanescent state in the MgAl2O4 barrier appear at k//=0, which reduces the TMR ratio of the MTJs significantly.