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 equa l to 0.30) compounds are obtained. The results 0.43 less than or equal to b eta 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 t o 4.38 are qualitatively different than those reported in the literature fo r 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 ex plain the observations. The hole-poor regions would dilute the magnetic lat tice and prevent the occurrence of long-range order. Also, a spin transitio n of the Co3+ ions at Te or the hole-poor regions (acting equivalently to m issed spin clusters in amorphous ferromagnets) could be the reason for the high beta value in the framework of a Heisenberg model. [S0163-1829(99)0280 1-5].