Observation of enhanced magnetocaloric properties with A-site deficiency in La0.67Sr0.33MnO3 manganite

Abstract

In this paper, we have studied the effect on the structural, magnetic and magnetocaloric properties of La and Sr-deficiencies in the La_0.67Sr_0.33MnO₃ compound. Rietveld refinement of the X-ray powder diffraction patterns confirms that all of the compounds have crystallized into a rhombohedral crystal symmetry with an Rc space group. X-ray photoelectron spectroscopy measurements revealed that the parent compound has a mixed valance of Mn³⁺/Mn⁴⁺, whereas Mn²⁺/Mn³⁺/Mn⁴⁺ mixed valency is found in the case of both La and Sr-deficient compounds. The La_0.67Sr_0.33MnO₃ compound shows a magnetic transition temperature of 365 K, while the La and Sr-deficient compounds exhibit transition temperatures of 367 K and 355 K, respectively. Among the studied compounds, the Sr-deficient compound shows the highest magnetic entropy change (ΔS_M) of 5.08 J kg⁻¹ K⁻¹ at 352 K for a 50 kOe field with a relative cooling power (RCP) of 142 J kg⁻¹ and an adiabatic temperature change of 3.48 K, while the parent and La-deficient compounds exhibit a −ΔS_M of 4.78 J kg⁻¹ K⁻¹ at 364 K and of 4.12 J kg⁻¹ K⁻¹ at 364 K, respectively. The temperature dependence of the electrical resistivity with and without applied magnetic fields reveals that the La-deficient compound has one order and the Sr-deficient compound has two orders of suppression in the electrical resistivity. Thus, the Sr-deficient compound shows promising behaviour for reduction of the magnetic transition temperature towards room temperature, along with an increase in the ΔS_M values, and enhancement in the electrical conductivity. Therefore, it could be possible to tune the transition temperature towards room temperature without compromising the magnetic entropy change in order to develop materials for magnetic refrigeration applications.