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,Ο) for this system. Effects of the double-exchange
interaction on the dispersion curves are shown.Comment: Latex, 3 pages, 3 figure