Emission Mossbauer study of CMR manganite La0.6Ca0.2MnO3 .1. Anomalous ferromagnetism

Using Co-57 emission Mossbauer technique, we present clear evidence that in Ca-doped manganite, the magnetic and paramagnetic phases coexist below T-C, with the abundance of the latter increasing with temperature. In contrast with the regular ferromagnetic materials, the variation of the hyperfine internal magnetic field H-int with temperature deviates considerably from the Brillouin relation, and exhibits an abrupt drop at T-C. These features characterize the magnetic transition as a first-order transition. The non-Brillouin behavior of H-int(T) and the temperature dependence of the shape of the magnetically split sextet indicate the presence of spin fluctuations in this material well below T-C. (C) 1997 American Institute of Physics.