Ni-Mn-X基合金奥氏体铁磁序对磁结构相变热滞的影响及其低场可逆性的研究

Ni-Mn-X基Heusler合金马氏体相变过程中磁与结构的耦合转变，带来了以磁驱结构相变为基础的丰富的物理效应。然而，高磁场驱动力与低相变热滞之间的相互牵制，成为了提升低场磁驱动相变可逆性的瓶颈。厘清母相奥氏体铁磁序对相变热滞的影响机制是提高磁驱动相变可逆性的前提和关键。对此，本项目将研究成分以及磁场、压力等外场对奥氏体铁磁序的建立和铁磁有序度的调控规律，系统研究铁磁有序度对母相晶体结构、磁性参数、微观组织以及马氏体相变热力学过程等的影响，建立奥氏体铁磁有序度、磁结构相变过程和相变热滞之间的内在关联，揭示铁磁序影响相变热滞的作用机制。基于此，发挥多手段协同作用，抑制相变热滞，平衡和优化热滞和磁场驱动力之间的关系，提升Ni-Mn-X基合金低场磁驱动相变的可逆性，并进一步推广应用于其它磁结构相变合金体系。本项目为深入理解磁结构相变的热滞行为提供依据，为实现低场可逆磁驱动相变提供可行的方案。

The coupling between magnetic and structural transitions in martensitic transformation brings about abundant physical effects on the basis of magnetic-field-induced structural-transition in Ni-Mn-X-based Heusler alloys. However, the mutual constraint between high magnetic-field-driving capacity and low thermal hysteresis of phase transition becomes the bottleneck in achieving the high reversibility of magnetic-field-induced structural-transition under low field. To clarify the influence mechanism of ferromagnetic order in austenitic parent phase on the thermal hysteresis of phase transition is the premise and key to develop the reversibility of magnetic-field-induced structural-transition. In this proposed project, the tuning rules of the establishment and degree of ferromagnetic order in austenite by composition, magnetic field and pressure will be investigated. The effects of degree of ferromagnetic order on the crystalline structure, magnetic parameter, microstructure of parent phase and the thermodynamics of martensitic transformation will be systematically explored. The internal correlations in the degree of austenitic ferromagnetic order, magnetostructural transformation and thermal hysteresis of phase transition will be established. And the influence mechanism of ferromagnetic order on the thermal hysteresis of phase transition will be revealed. Based on the exploration, the thermal hysteresis of phase transition will be suppressed, the relation between thermal hysteresis and magnetic-field-driving capacity will be optimized and balanced by coordinating the influences. The reversibility of magnetic-field-induced structural-transition under low field in Ni-Mn-X-based alloys will be improved. Furthermore, the mechanism will be generalized to other alloy systems with magnetostructural transformation. This research project can provide the theory to understand the thermal hysteresis behavior of magnetostructural transformation, and the feasible guideline to realize the reversible magnetic-field-induced structural-transition under low field.