Magnetocaloric effect and phase transformation of LaFe11.0M0.5Si1.5 (M = Cu, Ni, Mg) alloys

La (Fe,Si)13 is a promising magnetic refrigerant material. In this paper, the effects of Cu, Ni and Mg substitution of Fe on the magnetocaloric effect and phase transition properties of LaFe11.5Si1.5 alloys were studied by first-principles calculations combined with experiments. Through scanning electron microscopy–energy-dispersive spectroscopy analysis, it was concluded that after Cu partially replaced Fe, the content of the 1:13 main phase significantly decreased to 61.49%, and the contents of the α-Fe and LaFeSi phases increased. Cu was not conducive to the formation of the main phase. After Mg partially replaced Fe, the content of the 1:13 main phase increased to 99.12%, and Mg promoted the formation of the main phase. The electronic structure of the alloy was reconstructed by density functional theory (DFT), and the effects of the doping atoms on the magnetic properties of the alloys were studied. The calculation results showed that Ni atoms had the same weak magnetism as that in the magnetic moment vector direction of Fe atoms, Cu and Mg atoms had magnetism opposite to that in the magnetic moment vector direction of Fe atoms, and all alloys showed a lower total magnetic moment. According to the Arrott curve and the field dependence method of the magnetocaloric effect (MCE), when Cu = 0.5 and Ni = 0.5, the alloy phase transition changed from a first-order phase transition to a second-order phase transition, and when Mg = 0.5, the alloy still had a first-order phase transition.