Role of Mn2+ doped in La0.66-xCa0.33-yMn1+x+yO3 porous nanospheres: Structure, critical behavior, magnetocaloric effects and a first-order reversal curve analysis

In this study, the effects of A-site La and Ca defects with Mn2+ doping on the structure, magnetic phase transition, magnetocaloric effect, critical indices, and magnetic interactions of La0.66-xCa0.33-yMn1+x + yO3 porous nanospheres were investigated. The results indicated that the critical parameters of La0·66Ca0·33MnO3 porous nanospheres were similar to those of the short-range ordered Ising model. The A-site La-defect Mn2+ doping makes the critical parameters β and γ tend to the Ising model and mean-field model, respectively. When A-site Ca-defect Mn2+ doping is obtained, β and γ tend to follow the Ising model and 3D-Heisenberg model, respectively. The phase transition exhibited a second-order ferromagnetic-paramagnetic transition for all samples. The A-site defect Mn2+ doping in La0.66-xCa0.33-yMn1+x + yO3 porous nanospheres enhanced the Curie temperature to near room temperature without affecting magnetic entropy change. The effect of A-site defect Mn2+ doping on the magnetic interaction of La0.66-xCa0.33-yMn1+x + yO3 was visualized by the first-order reversal curve. The variation of interaction field distribution at the Curie temperature and 300 K indicated that exchange interaction was dominant at high temperature and dipole interaction was dominant at the Curie temperature.