Microstructure and isothermal magnetic entropy change of La(Fe0.89Si0.11)13 in a single-phase formation process by annealing

By annealing at 1323 K, the single-phase formation process of La(Fe0.89Si0.11)13 with a cubic NaZn13-type structure was investigated. A dendritic microstructure composed of an α-Fe phase with a mean size of about 10 μm and a LaFeSi phase in the as-solidified state is completely changed into the NaZn13-type single-phase by annealing for 300 h. The growth of the NaZn13-type phase is steep up to an annealing time ta = 100 h, and then becomes sluggish. As a result, the maximum isothermal magnetic entropy change, Δ S m max , markedly increases with increasing ta up to 100 h in response to the formation of the NaZn13-type phase. In addition, the position of Δ S m max shifts to higher temperature ranges due to the increase of the Curie temperature TC. Accordingly, thorough annealing for the single-phase formation of La(FexSi1−x)13 is important for high-performance magnetic refrigerants.