Effect of Fe on the microstructure and magnetic transition of Mn-Fe-P-Si Microwires

This work systematically investigated the effect of Fe content on the microstructure and magnetic transition behaviors of melt-extracting Mn-Fe-P-Si microwires. It was shown that the Fe content does not change the main phase of the samples, i.e. Fe₂P compound, which decreased with the increasement of Fe content. The transition temperature (T_tran) decreased from 311 to 245.5 K while the thermal hysteresis (T_hys) increased from 9.5 to 22.5 K increasing Fe from 0.90 to 1.05. The samples realized the first order magnetic transition at x = 1.00 and 1.05, correspondingly the samples demonstrated large magnetic hysteresis losses (W_y,) and isothermal magnetic entropy change (−∆S_iso^peak) at 5 T, 59.1 J kg⁻¹ and ¹4.5 J kg⁻¹ K⁻¹ for the sample x =1.00, 58.4 J kg⁻¹ and ¹5.8 J kg⁻¹ K⁻¹ for the sample x = 1.05. In contrast, the samples at x = 0.90 and 0.95 indicated second order transition character, and the W_y and −∆S_iso^peak were much smaller, i.e. ¹4.8 J kg⁻¹ and ¹0.3 J kg⁻¹ K⁻¹, 9.7 J kg⁻¹ and 10.7 J kg⁻¹ K⁻¹ respectively for the samples x = 0.90 and 0.95. The largest effective refrigerant capacity (RCE, 293.7 J kg⁻¹, 5 T) is found at x = 0.90. The reduced hysteresis and maintained competitive isothermal magnetic entropy change make the melt-extracting Mn-Fe-P-Si microwires with optimized Fe content as a promising magnetocaloric material family applied in real magnetic refrigeration applications.