Spin Wave Theory of Double Exchange Magnets

An isotropic half-metallic double exchange magnet with a direct superexchange coupling between the localized spins is studied within the spin-wave (1/S) expansion. The momentum dependence of the spin wave spectrum (including quantum corrections) in the ferromagnetic phase at T=0 is investigated. Based on the calculated spin wave spectrum of the canted state, it is shown that as long as the external magnetic field is not too strong, the double exchange -- superexchange competition does not result in a stabilization of a two-sublattice canted spin ordering.