Dynamic response in La0.55Ca0.45MnO3: temperature and field dependence

We report AC susceptibility measurements on bulk La0.55Ca0.45MnO3 as functions of temperature, DC field and frequency (f<1500 Hz). Both the in-phase (χ') and out-of-phase (χ'') parts of the response are studied. It is observed that the in-phase part goes through a maximum that is removed on the application of moderate DC fields. The temperature and field dependence of χ' are consistent with the picture of an inhomogeneous transition proceeding through a growth of clusters. DC fields suppress both the components with the strongest effects being at or close to Tc. The out of phase response is completely suppressed by fields of the order of a few hundred Gauss. The effect of the DC field is discussed in terms of the suppression of spin fluctuations close to Tc, and to the changes in coercivity for lower temperatures