Effect of Ca on the microstructure and magnetocaloric effects in the La1−xCaxFe11.5Si1.5 compounds

The effect of Ca on the microstructure and magnetocaloric effects has been investigated in the La_1−xCa_xFe_11.5Si_1.5 (x = 0, 0.1, 0.2 and 0.3) compounds. The introduction of Ca leads to the appearance of minor α-Fe and Ca-rich phases, which affects the actual compositions of the main phases for the Ca containing samples. With increasing the Ca concentration, the Curie temperature T_C increases from 183 to 208 K, and the maximum magnetic entropy changes |ΔS| at the respective T_C with a magnetic field change from 0 to 5 T are 21.3, 19.5, 16.9, and 11.2 J/kg K for x = 0, 0.1, 0.2, and 0.3, respectively. The nature of the magnetic transition changes from first-order to second-order with an increase in Ca concentration, which leads to a reduction of the hysteresis and a decrease of the magnetic entropy change. However, the relative cooling power for La_1−xCa_xFe_11.5Si_1.5 compounds remains comparable with or even larger than that of other magnetocaloric materials over a wide temperature range. The higher T_C and the smaller hysteresis in comparison with those of the parent compound suggest that the La_1−xCa_xFe_11.5Si_1.5 compounds could be suitable candidates for magnetic refrigerants in the corresponding temperature range.