Spin-wave excitations in the ferromagnetic metallic and in the charge-, orbital-, and spin-ordered states in Nd1-xSrxMnO3 with x approximate to 0.5

We report inelastic neutron-scattering experiments on single crystals of Nd1-xSrxMnO3 with x = 0.5 and x = 0.49. The spin-wave dispersion in the charge-, orbital-, and spin-ordered state in Nd0.5Sr0.5MnO3 exhibits a strongly anisotropic stiffness. The sign of the anisotropy is characteristic for the site-centered model for charge and orbital ordering in half doped manganites. Within this model, linear spin-wave theory yields a perfect description of the experimental dispersion. In the ferromagnetic metallic state of Nd1-xSrxMnO3 with x = 0.49 and x = 0.50 magnetic excitations exhibit nearly the same magnon dispersion. High intense signals near the zone boundary over a wide energy level overlap with a sharp spin-wave dispersion, which can be described with a Heisenberg model including nearest-neighbor interactions.