Structure and spin dynamics of La0.85Sr0.15MnO3

Neutron scattering has been used to study the structure and spin dynamics o f La0.85Sr0.15MnO3. The magnetic structure of this system is ferromagnetic below T(C)similar or equal to 235 K. We see anomalies in the Bragg peak int ensities and new superlattice peaks consistent with the onset of a spin-can ted phase below T(CA)similar to 205 K, which appears to be associated with a small gap at q=(0,0,0.5) in the spin-wave spectrum. Anomalies in the latt ice parameters indicate a concomitant lattice distortion. The long-waveleng th magnetic excitations are found to be conventional spin waves, with a gap less (< 0.02 meV) isotropic dispersion relation E = Dq(2). The spin stiffne ss constant D has a T-5/2 dependence at low T, and the damping at small q f ollows q(4)T(2). An anomalously strong quasielastic component, however, dev elops at small wave vector above similar to 200 K and dominates the fluctua tion spectrum as Ti Tc. At larger q, on the other hand, the magnetic excita tions become heavily damped at low temperatures, indicating that spin waves in this regime are not eigenstates of the system, while raising the temper ature dramatically increases the damping. The strength of the spin-wave dam ping also depends strongly on the symmetry direction in the crystal. These anomalous damping effects are likely due to the itinerant character of the e(g) electrons. [S0163-1829(98)02945-2].