MAGNETIC, STRUCTURAL, AND SPIN DYNAMICAL PROPERTIES OF LA1-XCAXMNO3

Neutron scattering has been used to study the magnetic order, spin dyn amics, and structural properties of La1-xCaxMnO3 in the ferromagnetic regime (0<x<1/2). For x=1/3(T-C=250 K) where the magnetoresistance eff ects are largest the system behaves as an ideal isotropic ferromagnet at low T, with a gapless (<0.04 meV) dispersion relation E=Dq(2) and D (T=0)approximate to 155 meV Angstrom(2). However, an anomalous diffusi ve component develops above similar to 200 K and dominates the fluctua tion spectrum as T-->T-C. A magnetic field strongly reduces this quasi elastic scattering, shifting the spectral weight into the spin wave co mponent of the fluctuation spectrum. (C) 1997 American Institute of Ph ysics.