Magnetocrystalline anisotropy and uniaxiality of MnAs/GaAs(100) films

TL;DR

This study explores the magnetic properties and anisotropy of epitaxial MnAs films on GaAs(100), revealing complex strain effects, significant magnetic moment enhancement, and insights from both experimental and theoretical approaches.

Contribution

It provides a comprehensive analysis of how epitaxial conditions influence magnetic behavior and anisotropy in MnAs films, combining experimental measurements with ab initio calculations.

Findings

Magnetic moment at saturation is significantly enhanced.

Anisotropy constants show a slight increase.

Orbital to spin moment ratio increases in the coexistence region.

Abstract

We present an investigation of the magnetic behavior of epitaxial MnAs films grown on GaAs(100). We address the dependence of the magnetic moment, ferromagnetic transition temperature ($T_c$) and magnetocrystalline anisotropy constants on epitaxial conditions. From thorough structural and magnetic investigations, our findings indicate a more complex relationship between strain and magnetic properties in MnAs films than a simple stretch/compression of the unit cell axes. While a small increase is seen in the anisotropy constants the enhancement of the magnetic moment at saturation is significant. X-ray magnetic circular dichroism results show a behavior of the spin- and orbital-moment which is consistent with a structural transition at $T_c$. In particular, we find that the ratio of the orbital to spin moment shows a marked increase in the coexistence region of the ferromagnetic $\alpha$- and paramagnetic $\beta$-phases, a result that is well in accord with the observed increase of the $c/a$-ratio in the same temperature region. The \textit{ab initio} density functional calculations reveal that the magnetic properties are more sensitive towards change in in-plane axis as compared to a change of the out-of-plane axis, which is explained by the analysis of band structures. The effects of electron correlation in MnAs using \textit{ab initio} dynamical mean field theory are also presented.