强织构无稀土双相永磁体的纳米晶体生长动力学及其磁畴演化

With the rare earth resources dwindling and its price increasing rapidly, the development of a new kind of rare earth free permanent magnet with high magnetic properties is not only the requirement for the magnetic industry, but also the major issue for the sustainable development of Chinese rare earth industry. In this project,based on the comprehensive knowledge of crystal growth dynamics, mechanics and micro-magnetic, a new kind of rare earth freeα-Fe/MnBi two-phase permanent magnets with strong texture and high density is prepared by the method of rapid solidification and hot pressing deformation. The effect of pressing deformation parameter, such as pressure, temperature, deformation rate and the amount of deformation, on nanocrysalline oriented growth dynamics and the evolution of the micro-magnetic domain structure behavior were researched in rare earth free α-Fe/Mn-based magnets.Also the reason was clarified that the micro-structure in the soft/hard magnetic alloys including the grain oriented growth, evolution of defect, the grain boundary state and its particle accumulation mode, determines the magnetic exchange coupling effect. The physical mechanism of the domain wall moving and domain structure evolution was investigated. The core issuer was to clarify the mechanism of the outfield inducing strong texture formation in rare earth free two-phase nanocrystals. We will reveal the internal impact about the effect strong texture on the exchange coupling between the magnetic moment changes and nanocrystals intrinsic spin/orbit coupling. The above results will contribute to the theoretical research for developing a new high-magnetic rare earth free permanent magnet and its micro-structure design.

随着稀土资源日益减少、价格迅猛增长，及时开发一类新型高磁性无稀土永磁体不但是磁性行业发展的要求，更是我国稀土产业可持续发展的重大课题之一。本项目基于晶体生长动力学、机械力学和微磁学的基础上，综合利用快速凝固和热压变形技术制备出新型强织构高密度无稀土α-Fe/Mn基纳米晶双相永磁块体；通过研究热压变形（压力、温度、变形速度及变形量等参数）外场作用下无稀土α-Fe/Mn基双相永磁体的纳米晶取向生长动力学和微磁畴结构的演化行为，揭示磁体中永磁体中的晶粒取向生长、缺陷形成、晶界状态及其颗粒堆积方式等微结构对磁交换耦合效应、畴壁移动和磁畴结构演化的影响规律及其控制机理；核心问题是阐明外场诱导无稀土双相纳米晶织构的形成机理，并从理论上揭示强织构与交换耦合、磁矩改变及纳米晶粒之间自旋/轨道耦合的内在关联，为开发新型高磁性无稀土永磁体的微结构设计及其可控技术提供理论。

随着稀土资源日益减少、价格迅猛增长，及时开发一类新型高磁性无稀土永磁体不但是磁性行业发展的要求，更是我国稀土产业可持续发展的重大课题之一。本项目基于晶体生长动力学、机械力学和微磁学的基础上，综合利用快速凝固和热压变形技术制备出新型强织构高密度无稀土α-Fe/Mn基纳米晶双相永磁块体，为开发新型高磁性无稀土永磁体的微结构设计及其可控技术提供理论。首先研究了球磨工艺对MnBi合金磁性能的影响表明MnBi的Hcj主要因素为Mn的含量（极显著因素），次要影响因素是球磨时间。成分Mn50Bi50、球磨时长2h，最优Hcj为1026.3kA/m和Br为7.5405 A•m2/kg。同时该样品在450K时有优良的高温特性，Hcj为1680kA/m。MnBi合金室温和高温的矫顽力机制均是成核反磁化机制。非稀土掺杂对MnBi合金磁性能的影响，表明随着Ga增加，MnBi合金的Br下降，Hcj呈上升趋势，样品取向度从0.74增至0.79。晶常数发生变化，居里温度下降，说明Ga掺杂不利于MnBi低温相的生成，但合金的磁晶各向异性提高。MnBi铸锭预退火后球磨，MnBi(LTP)相上升，Hcj和Br也大幅提高。MnBi系列磁粉中，经过不同温度退火Hcj最高温度为633K，Hcj为1040kA/m，同时Br达到最大值17.22 A•m2/kg。退火温度为633K×1h时，样品Hcj达到最大值1056kA/m，是铸锭未经退火的1.3倍。球磨12h时，IMnBi(101)/IBi(012 MnBi 低温相达到最大值。从XRD和TMA看出，Mn55Bi45和Nd4.5Fe76.5Nb0.5B18.5合金高能球磨后，其相组成为MnBi低温相、Bi相以及Nd2Fe14B,Fe3B和少量α-Fe相。Mn55Bi45和Nd4.5Fe76.5Nb0.5B18.5合金复合后的样品磁滞回线呈单一硬磁相行为，其Hcj随着Mn55Bi45含量的增加呈现先增加后减少的趋势。δM曲线和dD(H)/dH-H曲线表明，40% Mn55Bi45/ 60% Nd4.5Fe76.5Nb0.5B18.5交换作用较弱，Hcj较高。由于MnBi合金正矫顽力温度系数，40% Mn55Bi45/ 60% Nd4.5Fe76.5Nb0.5B18.5样品在298 K到350 K温度范围内呈现正的温度系数。