On the nature of ferromagnetism in Ga_{1-x}Mn_xAs semiconductors

TL;DR

This study uses ab initio density-functional theory calculations to analyze the electronic structure and magnetic interactions in Ga_{1-x}Mn_xAs semiconductors, revealing a localized hole-mediated ferromagnetic coupling.

Contribution

It provides detailed ab initio insights into the nature of hole states and Mn-Mn interactions, challenging effective-mass models and clarifying the ferromagnetic mechanism.

Findings

Holes form a dispersionless impurity band with p-like character.

Mn-Mn coupling is always ferromagnetic and mediated by holes.

The hole-Mn exchange coupling is estimated to be s=1/2 and S=5/2.

Abstract

We have performed ab initio calculations within the density-functional theory for Ga_{1-x}Mn_xAs diluted semiconductors. Total energy results unambiguously show that a quasi-localized down-spin hole, with strong p-like character, surrounds the fully polarized Mn up-spin d^5-electrons. Calculations indicate that the holes form an essentially dispersionless impurity band, thus rendering effective-mass descriptions of hole states open to challenge. We obtain estimates both for the s = 1/2 hole and S = 5/2 Mn exchange coupling, and for the distance dependence of the effective Mn-Mn exchange interaction. Results demonstrate that the effective Mn-Mn coupling is always ferromagnetic, thus non-RKKY, and intermediated by the antiferromagnetic coupling of each Mn spin to the holes.