Study On The Electromagnetic Properties Of NdFeB

Since M.S agawa, Croat and M.C.Koon reported the NdFeB permanent magnetism materials in 1983, NdFeB permanent magnet was wildly researched in the scientific field because of its excellent physical properties. NdFeB permanent magnet has high remanence, maximum magnetic energy product and high coercivity, which has the highest performance price ratio in the third generation the rare earth permanent magnet. NdFeB permanent magnet can be applied to many fields like as automobile, medical treatment, computer, machinery, military and so on with increasing expansion in applications.So far, less study is devoted to the basic micro structure on molecular and atomic level of NdFeB compared with productive technology, which is put more attraction due to the osculation with manufacture and application. This trend would effect the rapid development of NdFeB to some degrees in a long time. The study of the interaction and the structure on the atomic level could deeply proclaim physicochemical properties, and offer fundamental theoretical direction for the production and application of the material. Consequently, it is necessary to intensively discuss the microstructure, energy band, electronic transmission of NdFeB.In this paper, the first principle calculation, density function theory (DFT) and Non- equilibrium green function (NEGF) are used to investigate Nd₂Fe₁₄B unit cell, two-electrode model and magnetic tunnel junction's electronic structure, electron transmission, bandstructure, density of states and so on. Meantime, the optimum excitation parameters of two kinds of NdFeB magnetic materials (No.40 and No.52) have been measured. The major works in this paper are as follows:In Chapter I, we mainly introduced NdFeB permanent magnet's invention, development, physical properties, common preparation methods, application field and this paper's important significance.In chapter II, we described the basic theory knowledge and calculation methods used in this paper, including first principle, Density Function Theory, non-equilibrium green function(NEGF), Landuauer Theory and so forth. At the end of this chapter, the calculating software and laboratory equipments are introduced, such as VNL(ATK),MYC Magnetize and Demagnetize Controller and Agilent 6000 double-trace oscilloscope.In chapter III, according to the density function theory, using ATK we studied the essential structure properties and the electronic transmission of Nd₂Fe₁₄B unit cell and Au/ Nd₂Fe₁₄B /Au two-electrode model. Nd₂Fe₁₄B's bandstructure, electron density, density of states and Au/Nd₂Fe₁₄B/Au two-electrode model's electronic transmission, density of states were analyzed. We also calculated the R₂Fe₁₄B's bandstructure (R=Ce,Pr,Nd,Pm,Sm,Eu,Gd,Tb,Dy) and compared with Nd₂Fe₁₄B. The results show that Nd₂Fe₁₄B has typical band structure of conductor,which is a good conductor;the electron density of unit cell has perfect axial symmetry,which is corresponding to the atomic distribution of Nd₂Fe₁₄B. Electronic transmission has quasi-one-dimension properties,and quantum characteristics is very obvious. By comparing band structure of R₂Fe₁₄B compounds,we found that all R₂Fe₁₄B compounds which have been studied have band structure of conductor,and with increasing of the atomic number, in the same energy range, the number of energy levels shown a rising trend.In chapter IV,we built the Nd₂Fe₁₄B/MgO/Nd₂Fe₁₄B magnetic tunnel junction model in ATK. Its transport properties have been investigated theoretically by the density functional theory(DFT) and generalized gradient approximation (GGA). Under the SingleZetaPolarized (SZP) basis sets for all elements, we investigated Nd₂Fe₁₄B/MgO/Nd₂Fe₁₄B MTJ's electronic transmission, I-V curve and TMR. At 0 bias,the MTJ's TMR is 49.67%.In chapter V,the optimum excitation parameters of two kinds of bonded NdFeB magnetic materials (No.40 and No.52) have been measured based on the theory of electromagnetic induction. MYC Magnetize and Demagnetize Controller, Agilent 6000 double-trace oscilloscope are adopted. And the data was theoretical analysised and fitted. We controlled the pulse number through MYC Magnetize and Demagnetize Controller,adjusted exciting coil and excitation current and detected the effects of magnetizing of need checking sample at corresponding conditions, then got the optimum excitation parameters.At last, in chapter VI, we summaried the contents of the dissertation and draw a preview for future works.