Irreversible structure change of the as prepared FeMnP_1−xSi_x-structure on the initial cooling through the curie temperature

FeMnP_0.75Si_0.25 experiences a first order para- to ferromagnetic transition at about 200 K. In common with some other alloy compositions crystallizing in the Fe₂P structure, the magnetic transition of the as prepared alloy occurs at a lower temperature than on subsequent cooling events. This virgin effect is found to be accompanied by a magnetostrictively induced irreversible structure change that persists on succeeding cooling heating cycles. These findings provide means to understand and control the thermal hysteresis of the (Fe_1−xMn_x)₂P_1−ySi_y alloy system which is a promising material class for use in magnetocaloric refrigerators. - Highlights: • FeMnP_1−xSi_x exhibits a first order phase transition at the Curie temperature (T_c). • The lattice parameters exhibit a discontinuous change at the transition. • The structure is permanently altered by the initial cooling through T_c. • The transition temperature on cooling is enhanced by initial cooling. • Subsequent cooling/heating does not cause further changes of T_c