Influence of the oxidation on microstructure and magnetocaloric effect of LaFe11.5Si1.5C0.2 compounds

The oxidation of La-rich phase prevented the formation of the 1:13 phase in LaFe11.5Si1.5C0.2 compounds and α-Fe phase would grow large in the high-temperature annealing process. Moreover, the obtained 1:13 phase decomposed into a eutectic structure of α-Fe and La-rich oxide because of further oxidation. Owing to the oxidation, the Curie temperature of the remaining 1:13 phase increased. The maximum magnetic entropy change of the sample annealed for 3 d in an alumina crucible reached 17.8 Jkg−1 K−1 under a magnetic field change of 0-3 T, which is close to that of the sample annealed for 3 d in a quartz tube filled with argon (18.4 Jkg−1 K−1). In addition, magnetic hysteresis decreased for the sample which was annealed for 3 d in an alumina crucible. This implies short-term annealing process under a very low vacuum is practical for the preparation of some La(Fe, Si)13-based compounds.