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Abstract:
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.
