The temperature and field dependence of alternating-current (ac) susceptibility in a Ni 50 Mn 25 Ga 25 single crystal was measured using an ac susceptometer with a dc magnetic field oriented in the [100] and [110] directions, respectively. It is found that even at very low fields the premartensitic transition temperature decreases monotonically with the increase of the applied field, and it decreases more rapidly with field applied along the [110] direction than with field along the [100] direction. In accord with a previous model, present results confirm that the magnetoelastic interaction is responsible for the premartensitic transition, and the magnitude of the magnetoelastic interaction in the [110] direction is stronger than that in the [100] direction.
The effects of internal stress and bias field on transformation strain in the
Heusler alloy Ni52Mn24.4Ga23.6 were investigated.
It was found that both residual internal stress caused by the directional
solidification during the growth and additional bias field with a direction
consistent with the intrinsic preferential orientation would provide
favourable conditions for exhibiting large transformation strain and
magnetic-field-induced strain capability. These characteristics can be
attributed to either nucleating favourable variants or increasing the volume
fraction of favourable variants present through twin boundary motion.
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