Nearest-neighbour antiferromagnetic interaction as a limiting factor for critical temperature in model DMS system

TL;DR

This paper theoretically investigates how nearest-neighbour antiferromagnetic interactions limit the critical temperature in diluted magnetic semiconductors, highlighting the importance of magnetic inhomogeneity and clustering effects.

Contribution

It introduces a modified molecular field model that accounts for magnetic inhomogeneity and analyzes the impact of AF interactions on the ferromagnetic stability in DMS.

Findings

Critical temperature varies non-monotonically with magnetic ion concentration.

AF interactions significantly reduce the critical temperature at higher concentrations.

Behavior deviates from traditional homogeneous mean-field predictions.

Abstract

In numerous diluted magnetic semiconductor (DMS) systems, the competition takes place between the short-range antiferromagnetic (AF) superexchange interactions and the long-range Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling mediated by the charge carriers. Such a situation strongly influences the critical temperature, the maximization of which constitutes a challenging task in DMS physics and technology. The aim of the paper is to discuss theoretically the limiting effect of AF interactions between nearest-neighbour magnetic ions on the stability of inhomogeneous ferromagnetic state in a model diluted magnetic system reflecting some crucial features of DMS. The modified molecular field-based model is constructed to account for the magnetic inhomogeneity. The behavior of the system is studied as a function of the ratio of superexchange integral to effective ferromagnetic coupling integral, including the possibility of clustering/anticlustering tendency for the magnetic ions. The ground state of the system is analysed. The critical temperature is found to change non-monotonically with the concentration of magnetic ions and decrease severely for larger concentrations. The behavior of the system significantly differs from the predictions of the usual homogeneous mean-field model. Brief comparison with selected experimental results for (Zn,Mn)Te is provided.