Magnetic Instabilities and Phase Diagram of the Double-Exchange Model in Infinite Dimensions

Details Magnetic Instabilities and Phase Diagram of the Double-Exchange Model in Infinite Dimensions Magnetic Instabilities and Phase Diagram of the Double-Exchange Model in Infinite Dimensions

2006-04-16

arxiv.org/abs/cond-mat/0604392v1

Physics

Condensed Matter

Materials Science

38 pages, 11 figures, submitted to New Journal of Physics

Scientific paper

10.1088/1367-2630/8/7/116

Dynamical mean-field theory is used to study the magnetic instabilities and phase diagram of the double-exchange (DE) model with Hund's coupling J_H >0 in infinite dimensions. In addition to ferromagnetic (FM) and antiferromagnetic (AF) phases, the DE model supports a broad class of short-range ordered (SRO) states with extensive entropy and short-range magnetic order. For any site on the Bethe lattice, the correlation parameter q of a SRO state is given by the average q=, where theta_i is the angle between any spin and its neighbors. Unlike the FM (q=0) and AF (q=1) transitions, the transition temperature of a SRO state (T_{SRO}) with 00 but appears for J_H\neq 0. For p near 1, PS occurs between an AF with p=1 and either a SRO or a FM phase. The stability of a SRO state at T=0 can be understood by examining the interacting DOS,which is gapped for any nonzero J_H in an AF but only when J_H exceeds a critical value in a SRO state.

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