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 La_1.7Fe_11.6Si_1.4 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 La_1.7Fe_11.6Si_1.4 alloy, we have observed a significant field dependence of magnetostructural transition temperature (～ 6.3 K/T), resulting in a large and table-like entropy change (ΔS～ 18 J/kg·K in 2 T) over a broad temperature range (～ 10 K). Upon hydrogenation, the maximum value of ΔS keeps almost unchanged, while the Curie temperature increases up to 350 K. These results indicate that the investigated off-stoichiometric La(Fe,Si)₁₃ alloy is a promising magnetic material for magnetic refrigerators.