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-1 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. (c) 2006 Elsevier B.V. All rights reserved.