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Inelastic neutron scattering was used to systematically investigate the spinwave excitations (magnons) in ferromagnetic manganese perovskites. In spite of the large differences in the Curie temperatures (T C s) of different manganites, their low-temperature spin waves were found to have very similar dispersions with the zone boundary magnon softening. From the wavevector dependence of the magnon lifetime effects and its correlation with the dispersions of the optical phonon modes, we argue that a strong magnetoelastic coupling is responsible for the observed low temperature anomalous spin dynamical behavior of the manganites.

We have studied the spin dynamics in Pr 0.63 Sr 0.37 MnO 3 above and below the Curie temperature T C = 301 K. Three distinct new features have been observed: a softening of the magnon dispersion at the zone boundary for T < T C , significant broadening of the zone boundary magnons as T → T C , and no evidence for residual spin-wave like excitations just above T C . The results are inconsistent with double exchange models that have been successfully applied to higher T C samples, indicating an evolution of the spin system with decreasing T C .

We show the importance of the role of strain in La0.7Sr0.3MnO3 films by revealing the dominance of stress anisotropy effects over magnetocrystalline anisotropy effects in the magnetic anisotropy of these films. Magnetic anisotropy measurements of (001) and (110) La0.7Sr0.3MnO3 thin films on SrTiO3 and LaGaO3 substrates, with excellent structural quality, reveal twofold symmetry on (110) La0.7Sr0.3MnO3 films and fourfold symmetry on (001) films. Such symmetries can only be explained by stress anisotropy contributions in the plane of the film. In conjunction with the thickness dependence of the magnetic properties, the results indicate the dominant role of strain in the magnetic properties of these doped manganites.

Elastic and inelastic neutron scattering was used to study two ferromagnetic manganites A 1−x B x MnO 3 (x ≈ 0.3) with T c =197.9 K and 300.9 K. The spin dynamical behavior of these is similar at low temperatures, but drastically different at temperatures around T c . While the formation of spin clusters of size (∼ 20Å) dominates the spin dynamics of the 197.9 K sample close to T c , the paramagnetic to ferromagnetic transition for the 300.9 K sample is more conventional. These results, combined with seemingly inconsistent earlier reports, reveal clear systematics in the spin dynamics of the manganites.