Anomalous microstructure and magnetocaloric properties in off-stoichiometric La–Fe–Si and its hydride**Project supported by the National Natural Science Foundation of China (Grant No. 51371184) and the Outstanding Youth Fund of Zhejiang Province, China (Grant No. LR14E010001).

Abstract

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 (∼ 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.