Study of Magnetic and Magnetocaloric Properties of Calcium (Ca) Doped La_0.97-xCa_xHo_0.03MnO₃ Nanocomposites Synthesized by Facile Auto-Combustion Method

Magnetic refrigeration technology, which works on the magnetocaloric effect (MCE) of magnetic materials, has attracted the interest of numerous research groups over traditional gas refrigeration. It has several advantages, including being highly energy-efficient, environmentally friendly, and cost-effective. The major effort is directed in improving the magnetic entropy change along with the relative cooling power (RCP) of rare earth double perovskite oxide magnetocaloric materials. This study reports the magnetic and magnetocaloric properties of different concentration of alkaline earth metal such as Ca doped La_0.97-xCa_xHo_0.03MnO₃ (x = 0.3, 0.33 and 0.37) composites which were synthesized via the facile autocombustion technique. The second-order paramagnetic-to-ferromagnetic phase transition temperature appeared at the temperature-dependent field-cooled magnetization curve. The result do show that greater amount of Calcium enhanced the curie temperature, <i>T_c</i> up to 76 K. Ferromagnetic ordering was observed in these composites due to the existence of double exchange mechanism from both Mn³⁺ and Mn⁴⁺ ions that develops the electronic holes in Mn–O bands, which is favored by the doped Ca²⁺ ion. In addition, increasing the doping concentration of Calcium further increased change in magnetic entropy, <i>-△S_m</i> up to 0.21 J/Kg/K that led to have the result in higher RCP values. The fundamental key of this work is to demonstrate the potentiality of enhancing the magnetocaloric effect in the framework via spin coupling mechanism of Calcium doped rare earth perovskite compounds.