Interfacial giant tunnel magnetoresistance and bulk-induced large perpendicular magnetic anisotropy in (111)-oriented junctions with fcc ferromagnetic alloys: A first-principles study

TL;DR

This first-principles study reveals that (111)-oriented magnetic tunnel junctions with specific fcc ferromagnetic alloys exhibit giant tunnel magnetoresistance and large perpendicular magnetic anisotropy, driven by interface resonant tunneling and spin-orbit effects.

Contribution

The paper demonstrates high TMR ratios and large PMA in (111)-oriented MTJs with L1_1 alloys, highlighting the role of interface states and spin-orbit interactions, which is novel in this orientation and alloy configuration.

Findings

Co-based alloys achieve TMR over 2000%

CoPt exhibits the largest perpendicular magnetic anisotropy

Interface resonant tunneling is key to high TMR

Abstract

We study the tunnel magnetoresistance (TMR) effect and magnetocrystalline anisotropy in a series of magnetic tunnel junctions (MTJs) with $L1_1$-ordered fcc ferromagnetic alloys and MgO barrier along the [111] direction. Considering the (111)-oriented MTJs with different $L1_1$ alloys, we calculate their TMR ratios and magnetocrystalline anisotropies on the basis of the first-principles calculations. The analysis shows that the MTJs with Co-based alloys (CoNi, CoPt, and CoPd) have high TMR ratios over 2000$\%$. These MTJs have energetically favored Co-O interfaces where interfacial antibonding between Co $d$ and O $p$ states is formed around the Fermi level. We find that the resonant tunneling of the antibonding states, called the interface resonant tunneling, is the origin of the obtained high TMR ratios. Our calculation of the magnetocrystalline anisotropy shows that many $L1_1$ alloys have large perpendicular magnetic anisotropy (PMA). In particular, CoPt has the largest value of anisotropy energy $K_{\rm u} \approx 10\,{\rm MJ/m^3}$. We further conduct a perturbation analysis of the PMA with respect to the spin-orbit interaction and reveal that the large PMA in CoPt and CoNi mainly originates from spin-conserving perturbation processes around the Fermi level.