Critical behavior and magnetocaloric study in La0.6Sr0.4CoO3 cobaltite prepared by a sol–gel process

Abstract

The structure, magnetic properties, critical exponents and magnetocaloric effect (MCE) of La_0.6Sr_0.4CoO₃ cobaltite are studied. A sol–gel method is used in the preparation phase. Phase purity, structure, size, and crystallinity are investigated using XRD and SEM. The temperature dependent magnetization exhibits a sharp paramagnetic–ferromagnetic transition (FM–PM) at the Curie temperature T_C = 230 K. By means of several methods such as modified Arrott plots, the Kouvel–Fisher method, and Widom scaling relation, the values of β (corresponding to the spontaneous magnetisation), γ (corresponding to the initial susceptibility), δ (corresponding to the critical magnetisation isotherm) and T_C are estimated for La_0.6Sr_0.4CoO₃ around the FM–PM phase transition. Compared to standard models, the critical exponents obtained in our work are located near to those expected for the 3D Heisenberg model. Such results demonstrate the existence of ferromagnetic short-range order in La_0.6Sr_0.4CoO₃. With the obtained values, one can scale the magnetic-field dependences of magnetization below and above T_C following a single equation of state. In the vicinity of T_C, the magnetic entropy change ΔS reached maximum values of 1.1 and 2.1 J kg⁻¹ K⁻¹ under magnetic field variations of 2 and 5 T, respectively. The field dependence of the magnetic entropy changes are analyzed, which show power law dependence ΔS_max ≈ a(μ₀H)ⁿ at the transition temperature. Moreover, the temperature dependence of the exponent n for a different magnetic field is also studied. The values of n obey the Curie Weiss law above the transition temperature. It is shown that for La_0.6Sr_0.4CoO₃ cobaltite, the magnetic entropy change and n(T) follow a master curve behavior.