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 Ni2.14Mn 0.84Ga1.02 and Ni2.14Mn0.92Ga 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 Ni2.14Mn0.84Ga 1.02 increases linearly with increasing hydrostatic pressure; its increasing rate of about 4 K/GPa is well explained by using the Ehrenfest equation. © 2005 The Japan Institute of Metals.