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

Abstract

The effect of Ca on the microstructure and magnetocaloric effects has been investigated in the La1−xCaxFe11.5Si1.5 (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 TC increases from 183 to 208K, and the maximum magnetic entropy changes |ΔS| at the respective TC with a magnetic field change from 0 to 5T are 21.3, 19.5, 16.9, and 11.2J/kgK 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 La1−xCaxFe11.5Si1.5 compounds remains comparable with or even larger than that of other magnetocaloric materials over a wide temperature range. The higher TC and the smaller hysteresis in comparison with those of the parent compound suggest that the La1−xCaxFe11.5Si1.5 compounds could be suitable candidates for magnetic refrigerants in the corresponding temperature range.