外延生长Ni-Mn-Ga薄膜的马氏体相变与磁化行为机理研究

外延生长Ni–Mn-Ga哈斯勒合金薄膜具有多种优异的磁控功能行为，是智能传感驱动、新型固态制冷等领域中极具前景的候选材料。然而，对于目前研究较多的母相奥氏体为<001>取向的外延生长Ni–Mn-Ga薄膜，其复杂的多尺度微观组织、多种取向并存的马氏体变体组态，阻碍了磁场诱发马氏体变体再取向的发生，导致此类薄膜尚未获得大磁致应变。本项目从马氏体相变的取向关系入手，提出利用MgO(111)基板制备出母相奥氏体为<110>取向且只存在单一马氏体变体团的Ni–Mn-Ga合金薄膜，重点研究此类薄膜中只存在单一马氏体变体团的根本原因，阐明马氏体相变过程的变体选择机制，揭示其磁滞回线上存在两段“磁矩跳跃”现象的物理本质以及可逆磁场诱发马氏体变体再取向的机理，据此构建可逆磁场诱发马氏体变体再取向的理论模型，进而开发出磁控功能行为优异的薄膜，以期为外延生长Ni–Mn-Ga合金薄膜走向实用奠定理论和技术基础。

Epitaxial Ni–Mn-Ga Heusler alloy thin films are convinced as promising candidate materials in smart sensors and actuators, and solid-state refrigerators, owing to their excellent performances such as magnetic-field induced strain and magnetocaloric effect. However, for the epitaxial growth of Ni-Mn-Ga films with parent phase austenite < 001 > orientation, the complex multi-scale microstructure and the coexisting martensitic variant configuration hinder the occurrence of magnetic field induced martensitic variant reorientation, which results in the absence of large magnetic strain. Taking into account the orientation relationships of martensitic transformation, the present project intends to prepare epitaxial Ni-Mn-Ga alloy films on MgO(1 1 1) substrate with < 110 > orientation of parent phase austenite, which contain only a single martensite group having their martensite plate interfaces parallel to the substrate surface. The fundamental reason for the existence of only a single martensitic group in these films will be mainly studied. The mechanisms of martensite variant selection during martensitic transformation, reversible magnetic-field induced reorientation of martensite variants and the nature of “magnetization jump” in step like magnetic hysteresis loops will be explored and addressed. Besides, theoretical models will be developed for reversible magnetic-field induced martensite variant reorientation, being served as the guides to produce thin films with excellent performances. The present work will offer theoretical foundation and practical significance for the application of epitaxial Ni–Mn-based alloy thin films in micro-nano sensor and actuator devices.