Giant variation of the perpendicular magnetic anisotropy at Fe/MgO interfaces by oxygen migration: a first-principles study

TL;DR

This study uses first-principles calculations to explore how oxygen migration at Fe/MgO interfaces causes large variations in perpendicular magnetic anisotropy, revealing regimes of reversible and irreversible effects that influence VCMA efficiency.

Contribution

It provides a detailed ab initio analysis of oxygen migration effects on magnetic anisotropy and VCMA, highlighting the transition from reversible to irreversible regimes and their impact on device performance.

Findings

Surface anisotropy energy shows sigmoidal dependence on oxygen concentration.

VCMA efficiency saturates at about 54% oxygen migration, switching anisotropy from perpendicular to in-plane.

Reversible and irreversible oxygen displacements lead to different VCMA responses.

Abstract

A characteristic dependence of voltage control of perpendicular magnetic anisotropy (VCMA) on oxygen migration at Fe/MgO interfaces was revealed by performing systematic {\it ab initio} study of the energetics of the oxygen path around the interface. We find that the surface anisotropy energy exhibits a Boltzmann sigmoidal behavior as a function of the migrated O-atoms concentration. The obtained variation of the VCMA efficiency factor $\beta$ reveals a saturation limit beyond a critical concentration of migrated O, about $54\%$, at which the anisotropy switches from perpendicular to in plane. Furthermore, depending on the range of variation of the applied voltage, two regimes associated with reversible or irreversible ions displacement are predicted to occur, yielding different VCMA response. According to our findings, one can distinguish from the order of magnitude of $\beta$ the VCMA driving mechanism: an effect of several tens of fJ/(V.m) is likely associated to charge-mediated effect combined with slight reversible oxygen displacements whereas an effect of the order of thousands of fJ/(V.m) is more likely associated with irreversible oxygen ionic migration.