Effect of heat treatment conditions on MnFe(P,Si,B) compounds for room-temperature magnetic refrigeration

Abstract

Mn_1.000Fe_0.950P_0.595Si_0.330B_0.075compounds have been synthesized by high-energy ball milling and a subsequent solid-state reaction. The influence of the sintering conditions on the magnetic phase transition of Mn_1.00Fe_0.95P_0.595Si_0.33B_0.075samples has been systematically investigated using X-ray diffraction and magnetic measurements. The experimental results show that all the samples obtained after different heat treatment conditions crystallize in the Fe₂P-type hexagonal structure. The annealing temperature has a strong influence on the Curie temperature, which can be tuned between 265 and 298 K by sintering the samples at different temperatures between 1273 and 1373 K. The annealing time, however, does not significantly affect the Curie temperature. Both the annealing temperature and the annealing time have a significant effect on the magnetic entropy change. The magnetic entropy change under a magnetic field change of 1 T increases from 2.7 to 6.5 J kg⁻¹K⁻¹by increasing the annealing temperature from 1273 to 1373 K. By increasing the annealing time, the magnetic entropy change at first increases and then saturates after 20 h of heat treatment at 1373 K.