Effect of hydrostatic pressure on martensitic transformation in a ferromagnetic shape memory alloy Ni 2MnGa

Abstract

Ni 2MnGa transforms in the cooling process from the parent (P-) phase to the intermediate (I-) phase and then to the martensite (M-) phase. Under a uniaxial stress, a new phase (X-phase) appears, and the P → I transformation distinctively separates to the P → X, and the X → I transformations. In the present study, we have studied the effect of hydrostatic pressure on these transformation temperatures. As a result, we found that the distinct separation described above does not occur under a hydrostatic pressure of up to 0.9 GPa. The P → X and the I → M transformation temperatures increase with increasing hydrostatic pressure, and the ratio is 13.1 K/GPa and 16.2 K/GPa, respectively. The change in molar volume and/or thermal expansion coefficient associated with the transformation is estimated from these values.