Critical behavior in polycrystalline La0.7Sr0.3CoO3 from bulk magnetization study

The critical behavior of hole-doped perovskite cobaltite La0.7Sr0.3CoO3 has been investigated around the second-order paramagnetic-ferromagnetic (PM-FM) phase transition based on the static magnetization. Reliable critical exponents (beta = 0.272 +/- 0.001, gamma = 1.291 +/- 0.004, and delta = 5.54 +/- 0.02 with critical point T-C = 227.2 +/- 0.2 K) have been determined by using different techniques, including the Modified Arrott plot, the Kouvel-Fisher method, and critical isotherm analysis. The obtained critical exponents not only obey the Widom relation delta = 1+gamma/beta, but also can collapse the magnetization data M(H, T) into two curves below and above T-C following a single scaling equation M(H,epsilon) = epsilon(beta)f(+/-)(H/epsilon(beta+gamma)), which implies the reliability and accuracy of the exponents. Temperature variation of the effective exponents resemble with those for disordered ferromagnets. The exponents analysis related to the magnetocaloric effect is studied. The field dependence of the relative cooling power (RCP) is found to obey RCP proportional to H1+1/delta with the exponent delta. The asymptotic critical exponents (beta(eff) and gamma(eff)) are close to those predicted by 3D-Ising model with the exchange interaction J(r) decaying as r(-4.97) in the system, which reflects the existence of short-range FM coupling. (C) 2015 Elsevier B.V. All rights reserved.