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

Critical behaviors of the half-doped perovskite cobaltites Pr0.5Sr0.5CoO3-Δ (Δ=0 and ∼0.16) are investigated around the critical temperatures by bulk magnetization study, where the critical exponents (β, γ and δ) are obtained. These critical exponents fulfill the Widom scaling law δ=1+γβ-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-Δ accord with the mean-field model exactly. However, for the oxygen-stoichiometric Pr0.5Sr0.5CoO3,β deviates to the theoretical prediction of three-dimensional Heisenberg model while γ and δ are close to that of mean-field model. These results indicate long-range ferromagnetic coupling in Pr0.5Sr0.5CoO3−Δ (Δ=0 and ∼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 β 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.