无稀土永磁MnBi纳米线的可控制备与研究

Because of the limited availability and the enhancement of the cost of rare-earth resources, there is a growing interest in developing new rare-earth-free permanent magnetic materials. MnBi exhibits a positive temperature coefficient for coercivity which is unique in magnetic materials. So in this project, we select the MnBi alloy as subject and will prepare the rare-earth-free permanent magnet MnBi nanowires using templates assisted electrochemical deposition, so that the hard magnetic characters of MnBi materials can be enhanced using the structural property of MnBi nanowires. The effect of template characters and electrodeposition conditions on the composition and structure and magnetic properties of the MnBi nanowires will be studied and the impact of big length-to-diameter of MnBi nanowires to hard magnetic properties will be also explored, from which we can determine the contribution of shape anisotropy. Meanwhile we will carry out the micromagnetic simulation to further explore the mechanism of magnetization reversal and explore the relationship between the structure and magnetism and coercivity-temperature response of the MnBi nanowires, and at last ascertain the effect of the contribution from the shape anisotropy of nanowires in enhancement of the magnetism of MnBi nanomaterials. The results of this project will provide an important experimental guide for the using of one-dimensional materials in permanent magnet.

稀土资源的有限性和使用成本的提高，使得开发低成本、高性能的新型无稀土永磁材料成为研究热点。本项目以具有独特正矫顽力-温度系数的MnBi合金为研究对象，选用模板辅助电化学沉积法制备无稀土永磁MnBi纳米线，以期利用结构特性来进一步提高MnBi的硬磁性能。研究模板参数、电沉积条件对MnBi纳米线成分、结构和磁性的影响，探索纳米线不同长径比对硬磁性能的贡献，从而确定形状各向异性对MnBi磁性的影响。同时结合微磁模拟揭示其磁化反转机制，探索MnBi纳米线的结构与磁性和矫顽力-温度响应的关系，探明纳米线的形状各项异性在提高纳米MnBi磁性中的作用。该项目的研究成果将对一维纳米结构在永磁中的作用提供重要的实验依据。

低温相结构的锰铋合金由于具有高的矫顽力和独特的正矫顽力-温度系数而成为无稀土永磁体中极有希望的候选材料。本项目通过络合剂EDTA的加入，缩小了锰铋两种离子的还原电势差，并实现两者的可控沉积，从而实现电化学沉积方法对低温相锰铋合金的成功制备。锰铋比例在特定范围内时锰铋合金具有室温下的自发交换偏置现象。后期高温退火过程中快速降温有利于锰铋矫顽力的提高。扩展研究中组成成分铋膜形貌和结构随温度的变化有助于分析锰铋性能对温度的依赖关系。这些工作的完成对低温相锰铋材料的制备及其进一步应用提供了很好的实验指导。