Magnons in ferromagnetic metallic manganites

Ferromagnetic (FM) manganites, a group of likely half-metallic oxides, are of special interest not only because they are a testing ground for the classical double-exchange interaction mechanism for the 'colossal' magnetoresistance, but also because they exhibit an extraordinary arena of emergent phenomena. These emergent phenomena are related to the complexity associated with strong interplay between charge, spin, orbital, and lattice. In this review, we focus on the use of inelastic neutron scattering to study the spin dynamics, mainly the magnon excitations in this class of FM metallic materials. In particular, we discuss the unusual magnon softening and damping near the Brillouin zone boundary in relatively narrow-band compounds with strong Jahn-Teller lattice distortion and charge-orbital correlations. The anomalous behaviours of magnons in these compounds indicate the likelihood of cooperative excitations involving spin and lattice as well as orbital degrees of freedom.