Optimization of microstructure and magnetocaloric effect by heat treatment process in LaFe 11.7 Si 1.3 microwire

A large magnetocaloric effect and significantly shortened annealing process were obtained simultaneously in melt-extracted LaFe 11.7 Si 1.3 microwires. Large amounts of La(Fe,Si) 13 phases were formed within 5 min when annealed at 1353 K via a rapid peritectic reaction, because the nanoscale dendrites and a small amount of nanoscale La(Fe,Si) 13 phases discovered inside grains could provide a lot of nucleation sites. Thereby, the main phase in LaFe 11.7 Si 1.3 microwire after annealed at 1353 K for 5 min was La(Fe,Si) 13 phase, although a small quantity of α-Fe and La-rich phases still remained in the microstructure. The annealed LaFe 11.7 Si 1.3 microwires exhibited a first-order magnetic transition behavior and a large maximum magnetic entropy change of 7.7 J/kg K under a magnetic field of 1.4 T with negligible magnetic hysteresis. However, the strength of the first-order transition became weakened with the extension of annealing time. Finally, the working temperature range of LaFe 11.7 Si 1.3 microwires was elevated to room temperature by hydrogenation, which expanded the application of LaFe 11.7 Si 1.3 microwires in active magnetic regenerator.