Improvement of magnetocaloric effect in La(FexSi1-x)13 by dealing with inhibitory microstructures at high Fe concentration

Abstract

This is study aimed to improve the magnetic entropy change of the La(FexSi1-x)13 (1:13) phase by establishing high homogeneity at high Fe concentrations. For this purpose, the inhibition factors for obtaining the 1:13 phase in the as-cast state and subsequent annealed microstructures were analyzed. In the specimen with x > 0.90, the 1:13 phase was preferentially formed at one site (preferential site) and inhibited at another site (inhibition site). The inhibition site had a lamellar structure consisting of the PbFCl-type and Cu2Sb-type LaFeSi phases. These phases existed only in the inner part of the La-rich dendric arm, which was formed by an incomplete peritectic reaction. The nucleation of the 1:13 phase at the inhibition site scarcely occurred. In addition, the growth of the 1:13 phase around the preferential site was pinned by an untransformed domain around the inhibition site. Hot compression did not affect the deformation of the inhibition site. However, the 1:13 phase formation was accelerated in the Fe-rich specimens annealed after hot compression. This was due to an increase in the nucleation frequency around the preferential site and the faster conversion of the inhibition site into the 1:13 domains. As a result, a highly homogeneous 1:13 single phase was achieved via short annealing. A maximum magnetic entropy change of -26 J/kg K was obtained at 1 T and room temperature.