Optimization of microstructure and magnetocaloric effect by heat treatment process in LaFe_11.7Si_1.3 microwire

A large magnetocaloric effect and significantly shortened annealing process were obtained simultaneously in melt-extracted LaFe_11.7Si_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_11.7Si_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_11.7Si_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_11.7Si_1.3 microwires was elevated to room temperature by hydrogenation, which expanded the application of LaFe_11.7Si_1.3 microwires in active magnetic regenerator.