Half-Metallic Fe/MgO Superlattice: An Ideal Candidate for Magnetic Tunnel Junction Electrodes

TL;DR

This paper theoretically demonstrates that Fe/MgO superlattice electrodes in magnetic tunnel junctions can simultaneously achieve low magnetization, high perpendicular magnetic anisotropy, and high tunnel magnetoresistance, making them ideal for advanced STT-MRAM applications.

Contribution

It introduces Fe/MgO multilayers as a novel electrode material that exhibits half-metallicity and high TMR, advancing the design of magnetic tunnel junctions.

Findings

Fe/MgO multilayers exhibit half-metallicity near the Fermi level.

Increasing Fe/MgO layers shifts electron transport from direct tunneling to resonant tunneling.

Projected density of states shows gapped majority states and minority states at the Fermi energy.

Abstract

Magnetic Tunnel Junction (MTJ) based Spin-Transfer Torque Magnetic Random Access Memory (STT-MRAM) is poised to replace embedded Flash for advanced applications such as automotive microcontroller units. To achieve deeper technological adoption, MTJ needs to exhibit three key features: low magnetization (Ms), high perpendicular magnetic anisotropy (PMA) and high tunnel magnetoresistance (TMR). Here, we theoretically show that when Fe/MgO multilayers are inserted into the fixed and free layers of the MTJ, these three conditions are simultaneously met. As the number of Fe/MgO multilayers in MTJ electrodes is increased, we find that the electron transport evolves from direct barrier tunneling of majority spin states to the resonant tunneling of minority spin states. Remarkably, the projected density of states (PDOS) of Fe/MgO superlattice at the MgO tunnel barrier exhibits half-metallicity near the Fermi Energy, where the minority states exist while the majority states are gapped out, resulting in astronomically high TMR.