霍普金生效应和Nd_2Fe_(14)B/α-Fe交换耦合磁体的磁硬化机制  

Hopkinson Effect and Magnetic Hardening Mechanism of Nd_2Fe_( 14)B/α-Fe Exchange Coupling Magnets

作　　者：计齐根[1] 唐少龙[1] 章建荣[1] 阴津华[1] 都有为[1] 

机构地区：[1]国家固体微结构重点实验室,南京大学物理系,南京210093

出　　处：《南京大学学报（自然科学版）》2001年第5期605-612,共8页Journal of Nanjing University（Natural Science）

基　　金：国家重点基础研究项目 (G19990 6 45 0 8);江苏省自然科学基金 (JS -No .BJ970 43)

摘　　要：用快淬法制备了Nd7Fe86.5B5.5Ti(30wt %α Fe)纳米复合体薄带 ,研究了它在低场中的热磁性质 ,即霍普金生效应 (Hopkinsoneffect) .引入了磁体内部的磁阻碍分布函数 f(h(0 ) )来表示微磁结构的分布 ,发现实际磁体中钉扎和成核模型共同支配着磁体的硬磁化 ,它们的相对比率随着晶粒尺寸而异 ,远小于或远大于最佳晶粒尺寸 ,钉扎模型均成主体 .两种机制的合理平衡是得到最佳磁体性能的关键 。The Nd 7Fe 86.5B 5.5Ti (30 wt% α?Fe) nanocomposite ribbons are prepared by melt-spun method. The thermo-magnetic curves of no-saturated magnetization at lower applied field (H a<H c) as Hopkinson effect are measured and analyzed. The temperature dependence of the anisotropy K is considered as the origin of the Hopkinson effect of Nd 2Fe 14B?based magnet, due to its high value of the anisotropy K. A magnetic hindrance distribution function f(h 0) has been introduced to describe the unevenness of the magnetic hardening inside the magnet. The unevenness is originated from random grain orientations, different features of intergranular phase, varieties of grain size, uneven phase distributions and different hardening mechanisms. It is found that the hardening mechanism of an optimum quenched exchange-coupling magnet is a mixture of nucleation and pinning, and the ratio of those two mechanisms varies with the grain size. Far below or above this optimum grain size, the hardening will be dominated merely by the pinning mechanism, which originats from different pinning forces. In a group of excessive fine particles, the pinning force originats from the exchange coupling the single domain hard phase particles. Otherwise in a system consisting of coarse grains, the pinning force is provided by stresses, defects or impurities. The pinning force can be expressed roughly as h(T)=2α(K/μ 0M s) 1/2.?A certain ratio of these two mechanisms is essential to a well performing magnet. As for the coupling fine grains mean a lvigh remanence. for there is more coupling taking place between hard and soft phases. It is unfortunate that the excessive fine grain size not only decreases the anisotropy constant but also transfers the hardening mechanism from nucleation to pinning which reduces the coercivity. As for the hardening a perfect single domain particle will provide an optimum magnetic hardening force. A proper balance between these two factors is essential for a well performing nanocomposite. Optimum properties

关 键 词：霍普金生效应 钉扎模型 成核模型 磁硬化机制 Nd2Fe14B/α-Fe交换耦合磁体 矫顽力 

分 类 号：O482.5[理学—固体物理]