Short-Range Ordered Phase of the Double-Exchange Model in Infinite Dimensions

TL;DR

This paper investigates the phase diagram of the double-exchange model in infinite dimensions, revealing the existence of short-range ordered phases with higher transition temperatures than ferromagnetic or antiferromagnetic phases under certain conditions.

Contribution

It introduces the analysis of short-range ordered phases in the double-exchange model using dynamical mean-field theory, highlighting their stability and transition temperatures.

Findings

Short-range order (SRO) phases can have higher transition temperatures than FM and AF phases.

SRO states have lower energy than FM or AF for certain fillings at zero temperature.

Phase separation occurs for non-zero Hund's coupling J_H.

Abstract

Using dynamical mean-field theory, we have evaluated the magnetic instabilities and T=0 phase diagram of the double-exchange model on a Bethe lattice in infinite dimensions. In addition to ferromagnetic (FM) and antiferromagnetic (AF) phases, we also study a class of disordered phases with magnetic short-range order (SRO). In the weak-coupling limit, a SRO phase has a higher transition temperature than the AF phase for all fillings p below 1 and can even have a higher transition temperature than the FM phase. At T=0 and for small Hund's coupling J_H, a SRO state has lower energy than either the FM or AF phases for 0.26\le p < 1. Phase separation is absent in the J_H --> 0 limit but appears for any non-zero value of J_H.