Abstract
The magnetic and martensitic transformation properties of Ni50Mn25.2Fe2.8Ga22 ferromagnetic shape memory alloy were systematically investigated. The Curie temperature TC and the martensitic transformation temperature TM were determined. The temperature variations of the lattice parameters were measured by using an in situ X-ray powder diffractometer. This alloy crystallizes in cubic L21-type structure for the parent phase and the martensitic transformation was observed to start at 294 K with a small volume change ΔV. The effect of hydrostatic pressure on TC and TM was investigated by measuring the temperature dependence of the initial permeability at various pressures up to 9.4 kbar. It was found that TM increases with increasing pressure. By use of the Clausius-Clapeyron equation, the values of dTM/dp and ΔV determined in this study were found to be consistent with the result of the entropy change ΔS, which was estimated by thermoanalysis. On the other hand, TC was found to slightly decrease with increasing pressure, which is a unique behavior compared to other Ni2MnZ (Z = Ga, In, Sn, Sb) alloys. On the basis of the experimental results, the exchange mechanism of the Ni50Mn25.2Fe2.8Ga22 alloy is discussed.
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