Temperature evolution of the cluster state in La$_{0.8}$Ca$_{0.2}$MnO$_3$ and La$_{0.8}$Ca$_{0.2}$CoO$_3$

The results of investigations of the transport and magnetic properties (ac linear and nonlinear (second- and third-order) susceptibilities) of La$_{0.8}$Ca$_{0.2}$MnO$_3$ and La$_{0.8}$Ca$_{0.2}$CoO$_3$ single crystals have been presented. It has been found that both compounds in the paramagnetic phase contain ferromagnetic clusters with close magnetic characteristics. At high temperatures, ferromagnetic clusters nucleate in preferred sites associated with chemical inhomogeneities. Cooling below a specific temperature is accompanied by homogeneous nucleation of clusters. These two stages are observed in both compounds. In the doped cobaltite, the coalescence of clusters begins to develop at the third stage, whereas in the manganite, their behavior changes due to the development of ferromagnetic ordering of the matrix. These features indicate that the cluster state in doped manganites and cobaltites has a common nature. The difference in the behavior of ferromagnetic clusters is a consequence of the magnetically active character of the matrix in the case of manganites and the neutral character of the matrix in the case of cobaltites.