Effects of magnetic field and hydrostatic pressure on the martensitic transformation temperature of Ni–Mn–Ga ferromagnetic shape memory alloys

Change in martensitic transformation temperature by magnetic field and hydrostatic pressure has been investigated for single crystals of Ni2MnGa, Ni2.14Mn0.84Ga1.02 and Ni2.14Mn0.92Ga0.94, which exhibit P (parent phase)–I (intermediate phase)–10M, P–14M–2M and P–2M transformations, respectively. Following results are obtained: (i) the P–I transformation temperature does not change significantly by magnetic field; (ii) the I–10M and the P–14M transformation temperatures decrease up to 0.8 and 0.4 MA/m, respectively, and then increase by higher field; (iii) the P–2M transformation temperature increases linearly with increasing magnetic field; (iv) the 14M–2M transformation temperature increases up to 0.4 MA/m and decreases up to 0.8 MA/m and then increases again; (v) all the martensitic transformation temperatures increase linearly with increasing hydrostatic pressure. These results of (i)–(iv) are almost in good agreement with those calculated by the Clausius–Clapeyron equation.