The critical exponents of the second-order ferromagnetic-paramagnetic phase transition of ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{CoO}}_3$ $(0.20\mathrm{}<~x<~0.30)$ compounds are obtained. The results $0.43<~\beta <~0.46,$ $1.39<~\gamma <~1.43,$ and $4.02<~\delta <~4.38$ are qualitatively different than those reported in the literature for parent manganites, and are taken as the indication of the absence of long-range interactions below the Curie point. Electronic phase segregation in hole-rich ferromagnetic and hole-poor ${\mathrm{LaCoO}}_3$-like regions is supposed to explain the observations. The hole-poor regions would dilute the magnetic lattice and prevent the occurrence of long-range order. Also, a spin transition of the ${\mathrm{Co}}^{3+}$ ions at $T_C$ or the hole-poor regions (acting equivalently to missed spin clusters in amorphous ferromagnets) could be the reason for the high β value in the framework of a Heisenberg model.

• Received 22 July 1998

DOI:https://doi.org/10.1103/PhysRevB.59.123