Critical exponents of the ferromagnetic-paramagnetic phase transition of La1-xSrx CoO3 (0.20≤x≤0.30)

The critical exponents of the second-order ferromagnetic-paramagnetic phase transition of La1-xSrxCoO3 (0.20 less than or equal to x less than or equal to 0.30) compounds are obtained. The results 0.43 less than or equal to beta less than or equal to 0.46, 1.39 less than or equal to gamma less than or equal to 1.43, and 4.02 less than or equal to delta less than or equal to 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 LaCoO3-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 Co3+ ions at Te or the hole-poor regions (acting equivalently to missed spin clusters in amorphous ferromagnets) could be the reason for the high beta value in the framework of a Heisenberg model. [S0163-1829(99)02801-5].