Aggregation and magnetism of Cr, Mn, and Fe cations in GaN

TL;DR

This study uses first-principles calculations to explore how Cr, Mn, and Fe dopants aggregate and magnetize in GaN, revealing distinct magnetic behaviors and aggregation tendencies that align with experimental observations.

Contribution

It provides new predictions on magnetic ordering and aggregation tendencies of Cr, Mn, and Fe in GaN, improving understanding beyond previous DFT-GGA studies.

Findings

Cr and Mn tend to form ferromagnetic clusters with more than two atoms.

Fe clusters are antiferromagnetic and tend to aggregate.

Cr and Mn pairs are coupled ferromagnetically, Fe pairs are antiferromagnetically.

Abstract

A first-principles DFT-GGA+U study of the doping of GaN with Cr, Mn, or Fe confirms a strong tendency for the formation of embedded clusters occupying Ga sites of the wurtzite and zinc blende phases of GaN. Within the employed computation model, the tendency for aggregation is larger for Cr and Mn than for Fe. In contrast to previous DFT-GGA calculations, we predict a ferromagnetic ordering of the Cr and Mn clusters having more than two atoms while the Fe clusters are all antiferromagnetic. We have also investigated the magnetic ordering of nearest-neighboring ionic pairs that substitute gallium atoms at the (0001) wz-GaN surface. We find that Fe dopants tend to aggregate, whereas there is a repulsive interaction in the case of Cr and Mn. Nearest neighbor Mn and Fe pairs are coupled antiferromagnetically whereas the Cr pair is coupled ferromagnetically. The relevance of our finding to recent experimental findings is discussed.