Magnetic, structural, and spin dynamical properties of La1−xCaxMnO3

Neutron scattering has been used to study the magnetic order, spin dynamics, and structural properties of La1−xCaxMnO3 in the ferromagnetic regime (0<x<12). For x=13(TC=250 K) where the magnetoresistance effects are largest the system behaves as an ideal isotropic ferromagnet at low T, with a gapless (<0.04 meV) dispersion relation E=Dq2 and DT=0≈155 meV Å2. However, an anomalous diffusive component develops above ∼200 K and dominates the fluctuation spectrum as T→TC. A magnetic field strongly reduces this quasielastic scattering, shifting the spectral weight into the spin wave component of the fluctuation spectrum.