Effect of hydrostatic pressure on martensitic transformation in a ferromagnetic shape memory alloy Ni2MnGa

Ni2MnGa 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.

► There are four solid phases (P, X, I, M) in Ni2MnGa.
► The P–X and I–M transformation temperatures increase with increasing hydrostatic pressure.
► The X–I transformation temperature is almost independent of hydrostatic pressure.
► The volume change associated with these transformations is calculated using Clausius–Claperyron equation.