Spin interactions of interstitial Mn ions in ferromagnetic GaMnAs

TL;DR

This paper investigates the magnetic behavior of interstitial Mn ions in GaMnAs, revealing their limited role in ferromagnetism and the nature of their interactions, which differ based on their lattice positions.

Contribution

It provides a detailed analysis of the magnetic interactions of interstitial Mn ions in GaMnAs, highlighting their non-participation in ferromagnetism and the antiferromagnetic coupling in pairs.

Findings

Interstitial Mn ions do not participate in hole-induced ferromagnetism.

Mn interstitial pairs are antiferromagnetically coupled via superexchange.

Hexagonal interstitial Mn suppresses p-d interactions with holes.

Abstract

The recently reported Rutherford backscattering and particle-induced X-ray emission experiments have revealed that in low-temperature MBE grown GaMnAs a significant part of the incorporated Mn atoms occupies tetrahedral interstitial sites in the lattice. Here we study the magnetic properties of these interstitial ions. We show that they do not participate in the hole-induced ferromagnetism. Moreover, Mn interstitial double donors may form pairs with the nearest substitutional Mn acceptors - our calculations evidence that the spins in such pairs are antiferromagnetically coupled by the superexchange. We also show that for the Mn ion in the other, hexagonal, interstitial position (which seems to be the case in the GaMnBeAs samples) the p-d interactions with the holes, responsible for the ferromagnetism, are very much suppressed.