Thermodynamics of the Double Exchange Systems

TL;DR

This paper reviews recent non-perturbative studies of double exchange systems, focusing on their thermodynamic properties, spin fluctuations, and comparison with experimental colossal magnetoresistance manganites.

Contribution

It provides a comprehensive overview of advanced theoretical approaches beyond mean-field, including dynamical mean-field theory and Monte Carlo methods, applied to double exchange systems.

Findings

High Tc compounds like (La,Sr)MnO3 are canonical double-exchange systems.

Finite temperature properties are significantly affected by spin fluctuations.

Inhomogeneities and phase separation are relevant for lower Tc compounds.

Abstract

This article gives a comprehensive review on the recent studies of the double exchange systems using non-perturbative approaches; the dynamical mean-field theory and the Monte Carlo method. Investigations beyond mean-field type treatments are described. Taking into account strong spin fluctuations which create large changes in conduction electron structure, finite temperature properties as well as dynamics of the system are calculated. Comparisons with experimental data for colossal magnetoresistance manganites are made. We show that high Curie temperature (Tc) compounds, e.g. (La,Sr)MnO3, are canonical double-exchange systems. Properties of other compounds with lower Tc are discussed in relation to inhomogeneities of the system including the issue of phase separation.