Short and long range ordering in La1−xSrxCoO3 cobaltites
2019
Abstract We have carefully studied the relation between the critical and electrical behavior of rhombohedral La 1−x Sr x CoO 3 ( x = 0.2–0.5) compounds prepared by solid-state reactions. The results obtained from analyzing M ( T , H ) data indicate that all compounds undergo a second-order phase transition and the ferromagnetic-paramagnetic (FM-PM) transition temperature increases from approximate 182 K for x = 0.2 to 253 K for x = 0.5. Basing on the modified Arrott and Kouvel-Fisher techniques, scaling hypothesis, and critical isotherm analysis, we have determined the critical exponent values characteristic of magnetic order of La 1−x Sr x CoO 3 , with β = 0.361–0.489, γ = 1.021–1.346, and δ = 2.99–4.72. Interestingly, though all compounds are metallic ferromagnets, we have found the phase segregation in magnetic order as x > 0.3, where magnetic interactions tend to change from long-to-short-range FM order together with the absence of the insulating-like behavior at temperatures below 100 K. These phenomena are related to the spatial coexistence of multiple electronic and magnetic phases due to the changes in concentration of cobalt ions, spin-state transitions, and the existence of poor-hole anti-FM and hole-rich FM regions.
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