Emission Mössbauer study of CMR manganite La_0.8Ca_0.2MnO₃ .I. Anomalous ferromagnetism

Using ⁵⁷Co emission Mössbauer 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. Unlike the regular ferromagnetics, 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 magnetic transition as the first order one. 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.