Critical behavior of the half-doped perovskite Pr0.5Sr0.5CoO3-Δ

Critical behaviors of the half-doped perovskite cobaltites Pr0.5Sr0.5CoO3-Delta (Delta = 0 and similar to 0.16) are investigated around the critical temperatures by bulk magnetization study, where the critical exponents (beta, gamma and delta) are obtained. These critical exponents fulfill the Widom scaling law delta = 1 + gamma beta(-1), indicating self-consistency and reliability of the obtained results. With the critical exponents, M-T-H curves collapse onto two independent universal branches below and above the critical temperatures. The critical exponents of the oxygen-nonstoichiometric Pr0.5Sr0.5CoO3-Delta accord with the mean-field model exactly. However, for the oxygen-stoichiometric Pr0.5Sr0.5CoO3, beta deviates to the theoretical prediction of three-dimensional Heisenberg model while gamma and delta are close to that of mean-field model. These results indicate long-range ferromagnetic coupling in Pr0.5Sr0.5CoO3-Delta (Delta = 0 and similar to 0.16), which cannot be explained by the nearest-neighbor interaction proposed for the double-exchange mechanism. Instead, the collective effect of p - d hybridization and RKKY interaction of Pr3+ f-electrons with the conduction electrons is suggested to be responsible for the long-range interaction. In addition, the discrepancy of beta in the oxygen-stoichiometric Pr0.5Sr0.5CoO3 may be due to a short-range interaction corresponding to the extra crystalline phases in the oxygen-stoichiometric sample. (C) 2013 Elsevier B.V. All rights reserved.