Strength of the symmetry spin filtering effect in magnetic tunnel junctions

TL;DR

This paper investigates the symmetry spin filtering effect in Fe/MgO/Fe magnetic tunnel junctions, predicting a linear increase in TMR with barrier thickness and confirming it through ab initio calculations, which suggest potential for high TMR in device applications.

Contribution

The study provides a theoretical and computational analysis linking band structure properties to the strength of symmetry spin filtering, enabling rapid identification of materials for high TMR applications.

Findings

TMR increases linearly with MgO barrier thickness for Fe/MgO/Fe MTJs.

Ab initio calculations confirm the predicted strength of the symmetry spin filtering effect.

Predicted TMR exceeds 10,000% for N ≥ 8 layers, indicating high efficiency.

Abstract

Strength of the the symmetry spin filtering effect (as defined by the asymptotic behavior of the tunneling magnetoresistance (TMR) at large barrier thicknesses induced by this effect) is studied for the Fe/MgO/Fe magnetic tunnel junctions (MTJ). Based on the analysis of the band structure of bulk Fe and complex band structure of MgO we predict \emph{native} for the symmetry spin filtering effect linear increase of the TMR in Fe/MgO/Fe MTJ with increasing number of MgO layers, $N$. \emph{Ab initio} calculations of transmission functions performed for the Fe/MgO/Fe MTJ confirm our theoretical predictions for the strength of the symmetry spin filtering effect in broad range of energies and $N$. Our calculations also show that the \emph{combination} of the symmetry spin filtering effect and small surface transmission function in minority spin channel at the Fe/MgO interface is responsible for large $TMR>10,000\%$ predicted for Fe/MgO/Fe MTJ for $N \geqslant 8$. Proposed analysis of the strength of the symmetry filtering effect derived from the band structure of bulk electrode material could serve as a tool for quick material discovery search of suitable electrodes in context of emerging technologies that require high TMR.