Effect of Hydrostatic Pressure on P-14M-2M and P-2M Martensitic Transformations in Single Crystalline Ni–Mn–Ga Ferromagnetic Shape Memory Alloys

Abstract

Effect of hydrostatic pressure on martensitic transformation temperature has been investigated in single crystalline Ni_2.14Mn_0.84Ga_1.02 and Ni_2.14Mn_0.92Ga_0.94 ferromagnetic shape memory alloys, which exhibit P-14M-2M and P-2M transformations, respectively, where P stands for a parent phase. We found that all the martensitic transformation temperatures increase linearly with increasing hydrostatic pressure; their increasing rates against hydrostatic pressure are 3 K/GPa (P→14M), 13 K/GPa (14M→2M) and 7 K/GPa (P→2M). The volume changes associated with the transformations are calculated to be −0.04% (P→14M), −0.04% (14M→2M) and −0.15% (P→2M) by using the Clausius–Clapeyron equation. In addition, Curie temperature of the parent phase of Ni_2.14Mn_0.84Ga_1.02 increases linearly with increasing hydrostatic pressure; its increasing rate of about 4 K/GPa is well explained by using the Ehrenfest equation.