Ni50.5Mn24.5G25单晶的预马氏体相变特性

通过交流磁化率、电阻、有无磁场下的预相变应变、磁致伸缩和磁化强度测量，系统研究了近正配分比Ni505Mn245Ga25单晶的预马氏体相变特性.在自由样品中观察到预马氏体相变应变.在预相变点，沿010]方向施加大小约为80kA/m的磁场，在晶体母相的001]方向上获得了高达505ppm的磁致伸缩，该值是相同条件下晶体母相磁致伸缩量的5倍多.同时，报道了不同方向磁场对预相变应变干预的结果.利用软模凝结的概念和依据单晶生长的特点，分析了预相变应变产生的机理.而磁场干预预相变应变的机理是磁场增大的磁弹耦合导致的晶格形变与材料内禀形变的竞争.利用磁性测量结果证实和解释了预相变过程中001]和010]轴方向间进一步增大的各向异性.进而对磁场沿001]和010]两个晶体学方向所导致的应变特性的差别，包括最大磁致伸缩、饱和预相变应变、饱和场等，进行了分析和讨论. 关键词： 预马氏体相变 应变 磁致伸缩 磁弹耦合

Characteristics of the premartensitic transition in the Ni50.5Mn24.5G25 single crystals

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.