Magnetic and martensitic transformation properties under ambient and hydrostatic pressures of Ni50Mn25.2Fe2.8Ga22 ferromagnetic shape memory alloy

Abstract The magnetic and martensitic transformation properties of Ni 50 Mn 25.2 Fe 2.8 Ga 22 ferromagnetic shape memory alloy were systematically investigated. The Curie temperature T C and the martensitic transformation temperature T M 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 L2 1 -type structure for the parent phase and the martensitic transformation was observed to start at 294 K with a small volume change Δ V . The effect of hydrostatic pressure on T C and T M was investigated by measuring the temperature dependence of the initial permeability at various pressures up to 9.4 kbar. It was found that T M increases with increasing pressure. By use of the Clausius-Clapeyron equation, the values of d T M /d p and Δ V determined in this study were found to be consistent with the result of the entropy change Δ S , which was estimated by thermoanalysis. On the other hand, T C was found to slightly decrease with increasing pressure, which is a unique behavior compared to other Ni 2 MnZ (Z = Ga, In, Sn, Sb) alloys. On the basis of the experimental results, the exchange mechanism of the Ni 50 Mn 25.2 Fe 2.8 Ga 22 alloy is discussed.