Electronic and magnetic properties of substitutional Mn clusters in (Ga,Mn)As

TL;DR

This study uses first-principles calculations to analyze how Mn clusters affect the magnetic and electronic properties of (Ga,Mn)As, revealing that clusters influence hole localization and Curie temperature.

Contribution

It provides new insights into the effects of substitutional Mn clusters on the electronic structure and magnetic transition temperature of (Ga,Mn)As.

Findings

Mn clusters favor configurations with Mn surrounding a single As atom.

Hole distribution becomes localized at the cluster center as size increases.

Estimated Curie temperature is around 250 K with clusters, versus 600 K for uniform Mn distribution.

Abstract

The magnetization and hole distribution of Mn clusters in (Ga,Mn)As are investigated by all-electron total energy calculations using the projector augmented wave method within the density-functional formalism. It is found that the energetically most favorable clusters consist of Mn atoms surrounding one center As atom. As the Mn cluster grows the hole band at the Fermi level splits increasingly and the hole distribution gets increasingly localized at the center As atom. The hole distribution at large distances from the cluster does not depend significantly on the cluster size. As a consequence, the spin-flip energy differences of distant clusters are essentially independent of the cluster size. The Curie temperature $T_C$ is estimated directly from these spin-flip energies in the mean field approximation. When clusters are present estimated $T_C$ values are around 250 K independent of Mn concentration whereas for a uniform Mn distribution we estimate a $T_C$ of about 600 K.