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 LaFe11.7Si1.3 microwires. Large amounts of La(Fe,Si)13 phase was formed within 5 min when annealed at 1353 K via the 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 LaFe11.7Si1.3 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 LaFe11.7Si1.3 microwires exhibited 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 LaFe11.7Si1.3 microwires was elevated to room temperature by hydrogenation, which expanded the application of LaFe11.7Si1.3 microwires in active magnetic regenerator.