Impurity Effect on Ferromagnetic Transition in Double-Exchange Systems

TL;DR

This study investigates how impurities and randomness affect ferromagnetic transitions in double-exchange systems, revealing that disorder significantly suppresses ferromagnetism and destabilizes it more than previous models predicted.

Contribution

The paper provides an essentially exact Monte Carlo analysis of impurity effects on ferromagnetism in double-exchange models, highlighting the importance of fluctuations and spatial disorder.

Findings

Randomness suppresses ferromagnetism by reducing electron coherence.

Ferromagnetism becomes unstable more rapidly than previous predictions.

Critical temperature estimates are obtained from finite-size cluster simulations.

Abstract

Effect of randomness in the double-exchange model is studied. Large fluctuations and spatial random distribution of impurities are taken into account in an essentially exact manner by using the Monte Carlo calculation. The randomness suppresses the ferromagnetism by reducing the coherence of itinerant electrons. The suppression is significant in the critical region where the fluctuations are dominant. Temperature dependences of the magnetization are estimated for finite-size clusters. A characteristic temperature for phase transition $T^{*}$ is estimated from the inflection point, which is expected to give a good approximation for the critical temperature in the thermodynamic limit. Our results suggest that the ferromagnetism becomes unstable more rapidly than predicted in the previous theoretical results by the coherent-potential approximation.