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ABSTRACT: The magnetic properties and structural phase transformations of
Heusler alloys Ni<sub>2+x</sub>Mn<sub>1-x</sub>Ga and Ni<sub>2-x</sub>Mn
<sub>1+x/2</sub>Ga<sub>1+x/2</sub> were investigated. It was found that
the martensitic transformation temperature increases and the Curie
temperature decreases with decreasing Mn concentration in the Ni<sub>2+x
</sub>Mn<sub>1-x</sub>Ga system, but the magnetic properties decrease
faster than those do in the
Ni<sub>2-x</sub>Mn<sub>1+x/2</sub>Ga<sub>1+x/2</sub> system. This
suggests that the influence of the conduction electron concentration and
the distance between Mn atoms on the Curie temperature is stronger than
the magnetic dilution effect. The martensitic transformation temperature
shows a peak value at x=0.06 in the Ni<sub>2-x</sub>Mn<sub>1+x/2</sub>Ga
<sub>1+x/2</sub> system. A large stress-free magnetic-field-induced
strain (MFIS) of 1.8% has been obtained at room temperature in a single
crystal sample with the composition of the first system
IEEE Transactions on Magnetics 08/2001; · 1.36 Impact Factor
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ABSTRACT: The temperature and field dependence of alternating-current (ac) susceptibility in a Ni50Mn25Ga25 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.
Journal of Physics Condensed Matter 02/2001; 13(11):2607. · 2.55 Impact Factor
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ABSTRACT: Stress-free and two-way thermoelastic shape memory, with 1.2% strain and 6 K temperature hysteresis, has been found in single crystalline Ni52Mn24Ga24. The deformation can be enhanced more than three times, up to 4.0% shrinkage with a bias field 1.2 T applied along the measurement direction, or changed to 1.5% expansion by the 1.2 T applied perpendicular to the measurement direction. For achieving a large deformation, the magnetic field exhibits a more evident contribution than an external stress on this material. These characteristics can be attributed to the low level of internal stress and the preferential orientation of the martensitic variants. © 2000 American Institute of Physics.
Applied Physics Letters 11/2000; 77(20):3245-3247. · 3.84 Impact Factor
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ABSTRACT: 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.
Journal of Physics Condensed Matter 06/2000; 12(28):6287. · 2.55 Impact Factor
