On-site Coulomb interaction and the magnetism of (GaMn)N and (GaMn)As

TL;DR

This study investigates how on-site Coulomb interactions influence the magnetic properties of (GaMn)N and (GaMn)As, emphasizing the role of holes and computational methods in predicting Curie temperatures.

Contribution

It provides a comparative analysis of (GaMn)N and (GaMn)As using LDA and LDA+U schemes, revealing how Coulomb interactions and holes affect ferromagnetism and Curie temperature trends.

Findings

Holes are essential for ferromagnetism in both systems.

U increases hole delocalization and decreases p-d interaction.

Different trends in T_C for (GaMn)N and (GaMn)As at low Mn concentrations.

Abstract

We use the local density approximation (LDA) and LDA+U schemes to study the magnetism of (GaMn)As and (GaMn)N for a number of Mn concentrations and varying number of holes. We show that for both systems and both calculational schemes the presence of holes is crucial for establishing ferromagnetism. For both systems, the introduction of $U$ increases delocalization of the holes and, simultaneously, decreases the p-d interaction. Since these two trends exert opposite influences on the Mn-Mn exchange interaction the character of the variation of the Curie temperature (T$_C$) cannot be predicted without direct calculation. We show that the variation of T$_C$ is different for two systems. For low Mn concentrations we obtain the tendency to increasing T$_C$ in the case of (GaMn)N whereas an opposite tendency to decreasing T$_C$ is obtained for (GaMn)As. We reveal the origin of this difference by inspecting the properties of the densities of states and holes for both systems. The main body of calculations is performed within a supercell approach. The Curie temperatures calculated within the coherent potential approximation to atomic disorder are reported for comparison. Both approaches give similar qualitative behavior. The results of calculations are related to the experimental data.