Investigating the microstructure and magnetic properties of La-Fe-Si microwires during fabrication and heat treatment process.

In this study, the optimized fabrication and evolution of the microstructure and magnetic transition behavior of the melt-extraction LaFe 11.2 Si 1.8 microwires have been studied. After the optimization of extraction technique (heating power 22 KW, feeding rate 30–50 μm/s, rotation velocity 1700 r/min), the content of La(Fe,Si) 13 phase in the as-extracted microwires was 54 wt% due to the high solidification velocity, which was increased to 85 wt% via annealing at 1373 K for 20 min. The amount of La(Fe,Si) 13 phase was increased and the composition of La(Fe,Si) 13 phase became more homogenized through peritectic reaction and short-distance diffusion in the microwires during annealing process. The coexistence of the nanocrystalline and amorphous structures contributed to the broad magnetic transition temperature range of the as-extracted and annealed microwires. The annealed microwires exhibited a second-order magnetic transformation behavior and showed a maximum magnetic entropy change | ΔS M | max of 6.2 J/kg·K and working temperature interval of 36.0 K under a magnetic field of 20 kOe. Image 1 • LaFe 11.2 Si 1.8 microwires were prepared by melt-extraction technique. • The content of La(Fe,Si) 13 phase in the as-extracted microwire reached 54 wt%. • Nanoscale La(Fe,Si) 13 phase and α-Fe grains were formed in the extracted microwire. • 85 wt% La(Fe,Si) 13 phase was obtained in microwire annealed at 1373 K for 20 min. • The annealed microwire exhibited.| ΔS M | max 6.2 J/kg·K and ΔT FWHM 36.0 K under 20 kOe. [ABSTRACT FROM AUTHOR]