Magnon Excitations in Manganites

A review of experimental studies of magnon excitations in manganites is presented. Two kinds of techniques: the inelastic neutron scattering (in bulk materials) and the microwave resonance (in thin films) are considered. Experimental studies of spin dynamics by inelastic neutron scattering in metallic ferromagnetic manganites have shown that at low temperature for small wave vectors k → 0 the dispersion relation has a quadratic shape similar to that observed in Heisenberg ferromagnets. However, the above technique although very informative can be used only for sufficiently large samples of bulk materials. A complementary microwave resonance technique allows studying not only bulk properties, but also surface properties. There are two main theoretical approaches used to interpret the spin wave resonance spectra: the volume inhomogeneity and the surface inhomogeneity models. The last one introduced by Puszkarski has allowed for interpretation of the observed surface magnon excitations in thin films.