Ni_(51)Mn_(25.5)Ga_(23.5)单晶大的自发相变应变和磁感生应变

Giant Spontaneous Phase Transformation Strain and Magneticfield-induced Strain in Ni_(51)Mn_(25.5)Ga_(23.5) Single Crystal

通过交流磁化率、电阻、有无磁场下的马氏体相变应变测量,研究了Ni51Mn25.5Ga23.5单晶的马氏体相变和磁感生应变特性。伴随马氏体相变,该单晶展现出一个应变量高达-1.62%的自发双向形状记忆效应。采用磁场下冷却的方法,在材料的马氏体相获得了一个量值高达-1.5%且可逆的磁感生应变,该值近似为零场下冷却测量得到的磁感生应变的2倍。根据单晶生长机制和NiMnGa合金形状记忆特性,对上述结果进行了讨论。

Characteristics of the martensitic transformation and magnetic field-induced strain in Ni51 Mn25.5 Ga23.5 single crystal is investigated by the means of alternating-current magnetic susceptibility, resistance, and strain measurements with and without a biasing magnetic field. We deal the synthetical matieral with two-step annealing technics. As a result, a large spontaneous two-step shape memory effect with the strain high to -1.62% is found in the matieral after annealing. When the sample is cooled to the martensitic phase in a DC magnetic field applied perpendicular to the measuring direction of the strain, a large and reversible MFIS up to -1.5% is obtained. It indicates that the matieral possesses practical applications： This value of -1.5% is approximately two times larger than that detected in zero field cooling. And it is larger than the largest magnetic field-induced strain of -1.2% obtained in a free single crystal NiMnGa which was once reported. The results are discussed with respect to the growth mechanism of single crystals and the shape memory characteristics. The further analysis indicates that the mechanism of magnetic field-induced strain and magnetic enhancement transformation strain are attributed to the preferential orientation of the martensitic variants, which are induced by twin boundary motion along the magnetic field direction.