Effect of M/NM ratios on structural and magnetic properties of (Mn,Fe)2(P,Si) compounds

Abstract The (Mn,Fe)2(P,Si) compounds with large magnetocaloric effect are sensitive to the contents of impurity phase. In order to decrease its contents, the (MnFe)δ(P0.5Si0.5) (δ = 1.90, 1.95, 2.00, 2.05) compounds were designed and prepared by arc-melting method. The structure and magnetic properties were characterized by XRD, SEM, DSC and VSM, respectively. The diffraction analysis reveals that all samples are hexagonal Fe2P-type crystals with some impurity phase. The structure of impurity phase would change from cubic (Mn,Fe)3Si to hexagonal (Mn,Fe)5Si3 with decreasing δ from 2.05 to 1.90. And the Curie temperature of (MnFe)δ(P0.5Si0.5) compounds increased from 234 K for δ = 2.05–371 K for δ = 1.90. Meanwhile, the thermal hysteresis decreased by 58%. Under the field change of 5 T, the peak values of isothermal entropy change reaches 19.6 J‧kg−1‧K−1 for δ = 1.95. While, the maximal adiabatic temperature change increased by 47% as δ decreasing from 2.05 to 1.90. All results show that the impurity phase and magnetic properties of the (Mn,Fe)2(P,Si) compounds can be effectively tuned by adjusting M/NM ratios.