Room temperature magnetocaloric properties of Ni substituted La0.67Sr0.33MnO3

The magnetocaloric effect (MCE) in Ni substituted La0.67Sr0.33MnO3 (LSMO) has been studied to tune the magnetic transition temperature (TC) to room temperature and to increase the operating temperature range for MCE. The maximum magnetic entropy change (ΔSM) and relative cooling power (RCP) for La0.67Sr0.33Mn0.9Ni0.1O3 are found to be 3 J/kg K, 132 J/kg for a 50 kOe field change at 290 K, making it a promising candidate for magnetic refrigeration near room temperature. The effect of Ni on the structural, magnetic and critical exponent properties of polycrystalline La0.67Sr0.33Mn1−xNixO3 (x   = 0.05, 0.1, 0.33) powder samples prepared by the standard solid state reaction method was also carried out. The structural analysis using Rietveld refinement shows that all the compositions crystallize in the rhombohedral symmetry with R3¯c space group. A systematic decrease in the transition temperature is observed up on Ni substitution and a near room temperature TC (290 K) is achieved with x = 0.1 composition. The temperature dependant magnetization data of x = 0.05 and 0.1 shows a well-defined transition near TC. The addition of Ni weakens the Mn3+–O–Mn4+ double exchange interaction, which leads to a decrease in TC and magnetic moment in all the samples. The critical exponent analysis of x = 0.1 composition was done from the field dependence of magnetic entropy change and the obtained values are [β = 0.54, γ = 1.55 and δ = 3.85] close to the theoretical mean-field values.

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