Thermal-history dependent magnetoelastic transition in (Mn,Fe)₂(P,Si)

The thermal-history dependence of the magnetoelastic transition in (Mn, Fe)(2)( P, Si) compounds has been investigated using high-resolution neutron diffraction. As-prepared samples display a large difference in paramagnetic-ferromagnetic (PM- FM) transition temperature compared to cycled samples. The initial metastable state transforms into a lower-energy stable state when the as-prepared sample crosses the PM- FM transition for the first time. This additional transformation is irreversible around the transition temperature and increases the energy barrier which needs to be overcome through the PM- FM transition. Consequently, the transition temperature on first cooling is found to be lower than on subsequent cycles characterizing the so-called "virgin effect." High-temperature annealing can restore the cycled sample to the high-temperature metastable state, which leads to the recovery of the virgin effect. A model is proposed to interpret the formation and recovery of the virgin effect. (C) 2015 AIP Publishing LLC