Peculiar influence of Mn/Fe ratio on the magnetic and magnetocaloric properties of Mn2−xFexP0.6Si0.25Ge0.15 compounds

The influences of Mn/Fe ratio on the structural, magnetic and magnetocaloric properties of Mn2−xFexP0.6Si0.25Ge0.15 compounds with x = 0.7, 0.8, 0.9, and 1.0 have been investigated by means of X-ray diffraction and magnetization measurements. We find that the impurity phase (Mn,Fe)3(Si,Ge)1 disappears in the samples with higher Mn/Fe ratios. The change of Mn/Fe ratio induces a modification of the lattice dimension, which further leads to a change in the transition temperature. The observation of large thermal hysteresis indicates the occurrence of first-order phase transitions in all the studied samples. However, some characteristics of second-order phase transition have been observed in the isothermal magnetization curves and the isothermal entropy change (ΔST) curves for the samples with x = 0.7 and 0.8. The maximum values of ∣ΔST∣ under a field change from 0 to 9 T are found to be 8.9, 14.9, 22.2 and 22.4 J/kg K for x = 0.7, 0.8, 0.9 and 1.0, respectively.

► Increasing Mn/Fe ratio is favorable to the elimination of impurity phase.
► The studied Fe2P-type compounds undergo first-order phase transitions.
► Two Mn-rich compounds exhibit some characteristics of second-order transition.
► We have correctly determined the entropy changes of the studied compounds.
► The Fe2P-type compounds show large magnetocaloric effects.