Ni_(46)Mn_(35)Ga_(19)单晶中磁转变和马氏体相变的物理表征及形状记忆效应

Characterization of Magnetic Transition and Martensitic Transformation and Shape Memory Effect in Ni_(46)Mn_(35)Ga_(19) Single Crystal

NiMnGa是最早发现的铁磁形状记忆合金,是一种新型的形状记忆材料。自发现以来,许多学者对其进行了深入的研究,但对磁转变和马氏体转变共同发生的转变特性却缺乏系统的表征。本文采用多种测量手段,如相变潜热、电阻、交流磁化率和应变测量,对提拉法生长的Ni46Mn35Ga19单晶的磁转变和马氏体相变同时发生的转变行为进行了系统表征;根据合金形状记忆的特点和马氏体变体择优取向的机理,对实验结果进行了分析和讨论。应变测量结果表明,伴随该转变行为,材料展现出应变量达-0.89%的自发双向形状记忆效应和应变量高达-1.90%的磁控形状记忆效应。

As a new class of shape memory materials, the NiMnGa alloy is one of the earliest discovered magnetic shape memory alloy. Many scholars have investigated its characterizations and applications carried it out in-depth since its discovery, but actually in lack of systematic attribution to the co-occurrence of magnetic and martensitie transformations. In this paper the co-occurrence of magnetic and martensitic transformations in Ni46Mn35 Ga19 single crystal grown by the Czochralski method are characterized by various ways, such as heat flow, resistance, alternating-current magnetic susceptibility, and strain measurements. In addition, the experimental results are analyzed and discussed according to the characteristics of shape memory and the mechanism of preferential orientation of the martensitic variants. Accompanying with this transformation behavior, a large spontaneous transition strain of - 0.89% in zero field and a large magnetic-field-enhanced strain of - 1.90% are observed. This value of - 1.90% are approximately two times larger than that detected in zero field cooling.