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

TL;DR

This study investigates how thermal history affects the magnetoelastic transition in (Mn,Fe)2(P,Si) compounds, revealing an irreversible virgin effect and proposing a model for its formation and recovery.

Contribution

It introduces a detailed analysis of the thermal-history dependence of the magnetoelastic transition and proposes a model explaining the virgin effect in (Mn,Fe)2(P,Si).

Findings

As-prepared samples show a different PM-FM transition temperature than cycled samples.

The virgin effect is due to an irreversible transformation to a lower-energy state.

High temperature annealing can restore the initial metastable state.

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.