铁磁形状记忆合金Ni_(52.2)Mn_(23.8)Ga_(24)的马氏体相变及其物理表征

Martensitic transformation and physics characterization offerromagnetic shape memory alloy Ni_(52.2)Mn_(23.8)Ga_(24)

对Ni52 .2 Mn2 3 .8Ga2 4的单晶样品在马氏体相变过程中的相变潜热、磁性、电阻以及应变等物理序参量进行了测量 .测量结果表明 :不同的物理机制表征的相变温度有所不同 .利用马氏体相变的G T关系予以分析 ,解释了不同测量方法获得的相变温度差别的原因 .研究指出 ,Heusler合金Ni2 MnGa的相变是分布晶格畸变类型 ,磁结构的变化发生在第二步晶格的非均匀切变 ,但相变应变与G T模型有区别 .

We have measured the transformation temperature of Ni-52.2 Mn-23.8 Ga-24 single crystalline sample by various methods, such as DSC, magnetization, ac magnetic susceptibility, dc resistance, and transformation strain. Comparing the experimental results between each other, we found that, due to the different physical mechanism, various measuring methods will give different martensitic transformation temperatures. Based on these observations, we suggest a multi-step lattice deformation for the transformation of NiMnGa, which is similar to the G-T relation. The whole process of transformation can be observed by DSC and R-T measurements, while the magnetic measurements is only sensitive to the formation of martensitic lattices. The measurement on transformation strain is not so reliable for the transformation temperature as the other measurements, but it really reflects the situation of the sub-structures, such as twin boundaries, variants and defects in the material.