Anomalous microstructure and magnetocaloric properties in off-stoichiometric La-Fe-Si and its hydride

In the present work we reported the phase formation, microstructure, magnetocaloric effect and hydrogenation behavior of La-rich La1.7Fe11.6Si1.4 alloy. In this off-stoichiometric La(Fe, Si) 13 alloy, the NaZn13-type La(Fe,Si)(13) matrix phase shows faceted grains, with the Cr5B3-type La5Si3 used as the secondary phase distributed intergranularly. Such a peculiar morphology quickly forms upon one day annealing. In La1.7Fe11.6Si1.4 alloy, we have observed a significant field dependence of magnetostructural transition temperature (similar to 6.3 K/T), resulting in a large and table-like entropy change (Delta S similar to 18 J/kg.K in 2 T) over a broad temperature range (similar to 10 K). Upon hydrogenation, the maximum value of Delta S keeps almost unchanged, while the Curie temperature increases up to 350 K. These results indicate that the investigated offstoichiometric La(Fe,Si)(13) alloy is a promising magnetic material for magnetic refrigerators