The Exchange Parameters in Lanthanum Manganites

The spin-wave spectrum in the metallic ferromagnetic lantha-num cubic manganites was investigated. The interactions with four coordination spheres (32 neighbors) were taken into ac-count. The Heisenberg superexchange between all manganese ions as well as double exchange between the manganese ions with different valence were under consideration. The obtained magnon spectrum permits to investigate dispersion relations along an any crystallographic directions. This possibility was used for the numerical evaluation of the exchange parameters in the compounds La0.75Ca0.25MnO3 and La0.70Ca0.30MnO3 from the inelastic neutron scattering data.