Magnetic properties of La1−xCaxCoO3 single crystals

DC magnetization and optical measurements have been carried out for La1−xCaxCoO3 single crystals (x=0.1, 0.15, 0.2). The results indicate an inhomogeneous distribution of Ca2+ ions in a microscopic local scale, and existence of phase separation into a hole-rich ferromagnetic regions and a hole-poor host matrix. It was shown that with a temperature decrease the system evolves from a paramagnetic state of weakly interacting cobalt ions, through weakly interacting spin clusters, to the cluster glass state. The measured magnetic field dependences of magnetization have indicated that the volume of a hole-rich ferromagnetic cluster grows in magnetic field. These clusters can be considered as a precursor of the doping-induced ferromagnetic state. The analysis of the Curie-Weiss behavior at high temperature has shown that Ca doping stabilizes Co3+ ions in the intermediate spin state. Nevertheless, the small part of cobalt ions in the low spin state, up to about 10%, was suggested to exist for all levels of doping in paramagnetic phase up to room temperature. The long-time relaxation phenomena were found to follow a power law.