THERMAL HISTORY DEPENDENCE OF FIRST-ORDER MAGNETO-ELASTIC TRANSITION IN (MN,FE)2(P,SI) COMPOUNDS

摘要

In-situ high resolution neutron powder diffraction is used to study the peculiar “virgin effect” in the (Mn,Fe)_2(P,Si) compounds. Our results show that the “virgin effect” is related to the high-temperature meta-stable phase in the as-prepared sample, which is kept at room temperature after high-temperature annealing. The meta-stable phase is transformed to the low-temperature stable phase during the para-ferromagnetic transition upon first cooling, after which the “virgin effect” vanishes. High temperature annealing can “reset” the sample to the high-temperature meta-stable state, which leads to the recovery of the “virgin effect”. The energy barrier associated with the phase transformation from low-temperature phase to high-temperature meta-stable phase was calculated using thermodynamic analysis.