Structural, magnetic and magnetocaloric properties of 0.75La0.6Ca0.4MnO3/0.25La0.6Sr0.4MnO3 nanocomposite manganite

Abstract

The present study involves an investigation of structural, magnetic and magnetocaloric effect (MCE) properties of 0.75La_0.6Ca_0.4MnO₃/0.25La_0.6Sr_0.4MnO₃ composite material. Crystal structure analysis is performed by using Rietveld refinement of the X-ray diffraction patterns. The studied composite exhibits two structural phases; the rhombohedral and the orthorhombic structures corresponding to the mother compounds; La_0.6Ca_0.4MnO₃ and La_0.6Sr_0.4MnO₃, respectively. The scanning electron microscopy micrographs support our findings. Magnetic measurements as a function of temperature of the composite display two successive second order magnetic phase transitions at 255 and 365 K associated to both mother compounds. Therefore, a broadening of the magnetic entropy change peak is noted. A better relative cooling power (RCP) value of 360 J kg⁻¹ compared to those observed in mother compounds is obtained at μ₀H = 5 T, making of this material considered as a suitable candidate for magnetic refrigeration applications near room temperature. A consistent agreement between experimental results and numerical calculations based on the rule of mixtures has been shown. The theoretical modeling of the MCE using Landau theory reveals an acceptable concordance with experimental data indicating the importance of magnetoelastic coupling and electron interaction in the MCE properties of manganite systems. The field dependence of the magnetic entropy change is applied to study the critical behavior. Our results go in tandem with the values corresponding to the mean field model. The spontaneous magnetization values determined using the magnetic entropy change (ΔS_M vs. M²) are in good agreement with those found from the classical extrapolation of Arrott curves (μ₀H/M vs. M²).