Global versus Local Ferromagnetism in a Model for Diluted Magnetic Semiconductors Studied with Monte Carlo Techniques

TL;DR

This study uses Monte Carlo simulations to analyze a model for diluted magnetic semiconductors, revealing inhomogeneous ferromagnetic droplet states with critical temperatures lower than Hartree-Fock predictions, and highlighting the effects of disorder and doping.

Contribution

It provides the first Monte Carlo analysis of the model, showing the importance of inhomogeneous droplet states and refining critical temperature estimates compared to Hartree-Fock methods.

Findings

Critical temperatures are lower than Hartree-Fock predictions.

Ferromagnetic droplets form below a certain temperature scale.

Disorder does not significantly enhance ferromagnetism.

Abstract

A model recently introduced for diluted magnetic semiconductors by Berciu and Bhatt (PRL 87, 107203 (2001)) is studied with a Monte Carlo technique, and the results are compared to Hartree-Fock calculations. For doping rates close to the experimentally observed metal-insulator transition, a picture dominated by ferromagnetic droplets formed below a T* scale emerges. The moments of these droplets align as the temperature is lowered below a critical value Tc<T*. Our Monte Carlo investigations provide critical temperatures considerably smaller than Hartree-Fock predictions. Disorder does not seem to enhance ferromagnetism substantially. The inhomogeneous droplet state should be strongly susceptible to changes in doping and external fields.