Characteristics of the premartensitic transition in the Ni50.5Mn24.5G25 single crystals
Ni50.5Mn24.5G25单晶的预马氏体相变特性

The characteristics of premartensitic transition on nearly stoichiometric Ni \{50.5\}Mn \{24.5\}Ga \{25\} single crystals have been investigated systematically by various methods,such as the ac magnetic susceptibility,resistance,magnetostriction,premartensitic transition strain and magnetization measurement. The premartensitic transition strain in free samples was reported,and the enhanced premartensitic transition strain with an external magnetic field applied along the different directions was investigated. A large magnetostriction up to 505ppm in the \ direction of the parent phase is obtained in a pulse magnetic field of about 80kA/m applied along the \ direction at the premartensitic transition point,which is over five times larger than that in the parent phase. Based on the soft mode condensation and characteristic of the crystal growth,the mechanism of the premartensitic transition strain was analyzed. The effect of magnetic field intervened premartensitic transition strain is attributed to the competition between the crystal lattice deformation induced by the enhancing magnetoelastic coupling and the intrinsic deformation originated from the soft-mode condensation. We found that the premartensitic transition further generated the anisotropy between two crystallographic directions of \ and \,which is proved by the magnetization measurement. Furthermore,the resulting strain properties,such as the largest magnetostriction,the saturated premartensitic transition strain and saturated field,have been discussed in detail.