Role of Ca2+ doping on the structure, magnetic, and magnetocaloric properties of La0.75Gd0.05Sr0.2-xCaxMnO3 (x=0, 0.05, 0.075, and 0.10) perovskite manganites

In this paper, La0.75Gd0.05Sr0.2-xCaxMnO3 perovskite manganites were synthesized by the sol-gel method, and the effects of Ca2+ (x = 0, 0.05, 0.075, and 0.10) doping on the structural, magnetic, and magnetocaloric properties of the samples were investigated. All the samples exhibited a rhombic structure with R-3c space group symmetry; however, the incorporation of calcium ions leads to an increase in the Mn-O bond length and a reduction in the Mn-O-Mn bond angle, which weakens the double exchange effect and lowers the Curie temperature of the sample. For all the samples, it was demonstrated that the types of ferromagnetic-paramagnetic were second-order magnetic phase transitions. The magnetic entropy changes of the samples were also found to be positively correlated with the amount of Ca2+ doping, indicating that this group of samples is a suitable candidate for room-temperature magnetic refrigeration materials.