Magnetoresistance and transformation hysteresis in the Ni ₅₀Mn_34.4In_15.6 metamagnetic shape memory alloy

Temperature dependence of the equilibrium transformation field (H ₀) for Ni₅₀Mn_34.4In_15.6 metamagnetic shape memory alloy was precisely determined by electrical resistivity measurements using a pulsed magnet. The H₀-T curve was found to exhibit a maximum at around 50 K, suggesting that the transformation entropy change becomes negative in the lower temperature region. The residual electrical resistivity in the field-induced parent phase at lower temperatures was about 10 × 10^-8 Ω·m, being normal value as the ferromagnetic alloys, whereas that in the martensite phase was high of about 200 × 10^-8 Ω·m. The temperature dependence of the magnetic field hysteresis can be well fitted with the Seeger's theory proposed for plastic deformation by dislocations.