Dynamic response in CMR magnets

We report ac susceptibility measurements on bulk La/sub 0.55/Ca/sub 0.45/MnO/sub 3/ as functions of temperature, dc field and frequency (f <1 500Hz). Both the in-phase (lamda) and out of phase (lamda) parts of the response and 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 lamda 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. (author)