Simulations of a classical spin system with competing superexchange and double-exchange interactions

TL;DR

This paper uses Monte Carlo and spin-dynamics simulations to explore the phase diagram and dynamic properties of a classical spin system with competing interactions, relevant for magnetic materials like doped manganites exhibiting colossal magnetoresistance.

Contribution

It provides the first comprehensive phase diagram and dynamic structure factor analysis for a classical spin model with superexchange and double-exchange interactions.

Findings

Identification of two phases with unequal sublattice magnetizations.

Effects of double-exchange interactions on spin-wave dispersion.

Dynamic structure factor characterized for the model.

Abstract

Monte-Carlo simulations and ground-state calculations have been used to map out the phase diagram of a system of classical spins, on a simple cubic lattice, where nearest-neighbor pairs of spins are coupled via competing antiferromagnetic superexchange and ferromagnetic double-exchange interactions. For a certain range of parameters, this model is relevant for some magnetic materials, such as doped manganites, which exhibit the remarkable colossal magnetoresistance effect. The phase diagram includes two regions in which the two sublattice magnetizations differ in magnitude. Spin-dynamics simulations have been used to compute the time- and space-displaced spin-spin correlation functions, and their Fourier transforms, which yield the dynamic structure factor $S(q,\omega)$ for this system. Effects of the double-exchange interaction on the dispersion curves are shown.