MnCoGe基合金低磁场驱动变磁性相变及磁致效应研究

MnCoGe基合金因其高饱和磁矩和可调控的磁马氏体相变，正成为具有研发潜力的磁性多功能材料，然而过高的相变驱动场和差的力学性能，严重限制了该类合金的研发和应用。研究发现，提高Mn磁矩的不稳定性以增强马氏体相变对磁场的敏感度，有望在低场下实现磁场驱动变磁性相变。因此本项目拟以MnCoGe基合金为研究对象，通过设计合适成分和优化制备工艺提高Mn磁矩的不稳定性，进而降低相变驱动场；采用和低熔点金属(Sn或In等)热压的方法提高合金力学性能。前期预研结果表明，在调节Mn/Co比例的MnCoGe合金中观察到了低场驱动变磁性相变。本项目将对磁场驱动相变的发生规律及其表征和基于磁驱相变机制的磁热、磁致应变和磁电阻等物理效应及潜在应用展开研究；利用中子衍射、同步辐射结合第一性原理计算、相场模拟等手段探究合金磁场驱动相变和相关物理效应的微观机制，为MnCoGe基磁性多功能材料的研发及应用奠定理论和实验基础。

MnCoGe-based alloys are the potential magnetic multifunctional materials due to their high saturation magnetization and controllable magnetic martensitic transformation. However, high critical field to arouse the metamagnetic martensitic transformation and poor mechanical properties strongly limit their research and application fields. Previous studies have shown that low magnetic-filed-driven metamagnetic transformation would be realized by improving the instability of Mn magnetic moment to enhance the sensitivity of martensitic transformation to magnetic field. Therefore, the MnCoGe-based alloys are chosen as the research object in this project. We intend to increase the instability of Mn magnetic moment via designing appropriate chemical composition and optimizing preparation conditions, and accordingly enhance the sensibility of martensitic transformation to applied field, lowering the driving field of phase transition. Meanwhile, the mechanical property will be improved by hot-pressing the MnCoGe-base alloys, undergoing the metamagnetic transformation, with low melting point metals (Sn or In, et. al.). Our preliminary research results indicate that the metamagnetic transformation driven by a low applied field was observed in MnCoGe alloy by controlling the Mn/Co ratio. This project is aimed to investigate the occurrence regularity and characterization of magnetic-field-driven transformation, and associated physical effects and potential applications, based on the magnetic-field-driven transformation, such as magnetocaloric effect, magnetostriction, and magnetoresistance and so on. Meanwhile, in order to lay the theoretical and experimental foundations for the research and application of MnCoGe-based magnetic multifunctional materials, this project will also explore the physical mechanism of the magnetic-field-induced transformation and related physical effects by combining the neutron diffraction and synchrotron radiation techniques with the first-principle calculations and phase field simulation means.