Spin dynamics of strongly doped La1-xSrxMnO3

Cold neutron triple-axis measurements have been used to investigate the nat ure of the long-wavelength spin dynamics in strongly doped La1-xSrxMnO3 sin gle crystals with x = 0.2 and 0.3. Both systems behave like isotropic ferro magnets at low T, with a gapless (E-0<0.02 meV) quadratic dispersion relati on E = E-0 + Dq(2). The values of the spin-wave stiffness constant D are la rge (D-T=0 = 167 meV Angstrom(2) for x = 0.2 and D-T=0 = 176 meV Angstrom(2 ) for x = 0.3), which directly shows that the electron transfer energy for the d band is large. D exhibits a power law behavior as a function of tempe rature, and appears to collapse as T-->T-C Te. Nevertheless, an anomalously strong quasielastic central component develops and dominates the fluctuati on spectrum as T-->T-C. Bragg scattering indicates that the magnetization n ear T-C exhibits power law behavior, with beta similar or equal to 0.30 for both systems, as expected for a three-dimensional ferromagnet. (C) 1998 Am erican Institute of Physics.