| The maximum magnetic energy product of Nd-Fe-B permanent magnets which are so-called as the third generation of rare-earth permanent magnets is close to the theoretical limit value. So preparing a Nd-Fe-B magnet with higher maximum magnetic energy product than the present one has become a hot topic., The new nano and micron materials, which can be used widely, have the advantages of permanent magnets and nanometer materials. In the present thesis, firstly, nano-micron magnets were prepared using different coating materials and coating processes, and the magnetic properties of the obtained samples were compared. Secondly, using the magnetization and demagnetization curves of the anisotropic Nd2Fei4B/a-Fe permanent bulks, the existence and the strength of the exchange coupling were examined.Thirdly, the magnets were annealed under magnetic field, and the magnetic property and microstructure of the samples were studied.The anisotropic Nd2Fei4B/a-Fe permanent magnets were prepared by coating, orientation profiling, and isostatic pressing, annealing treatment. The composition, thermal performance, structure and magnetic property of the permanent magnets were researched by means of XRD, DTA, SEM, and B-H. The XRD results showed that the content of a-Fe in the magnets was improved by using both methods; DTA results showed that the sintering temperature changed insignificantly. Furthermore, the composition of the properties was carried out between the samples with good and bad qualities.The results of ultrasonic chemistry reactive coating (UCRC) indicated that the existence of Nd-and Fe-oxides affects the fracture mode of the boundary phase. The samples present the best magnetic property at10%, that is, the remanence is1.351T, the coercivity is819.7KA/m, and the maximum magnetic energy product is up to317.2KJ/m3. The values of the remanence, coercivity, and maximum magnetic energy product are1.261T,782.2KA/m and274.3KJ/m3, respectively, for the sample with5%Fe-coating in weight prepared using ultrasonic coating method.The magnetizing and demagnetizingcurves, as well the magnetization loops of the sintered anisotropic magnets prepared by different ways were obtained by B-H hysteresis Tester. The calculation of δM(H) indicates that there is exchange coupling between the hard and soft magnetic phases.The magnetic properties of the magnets were changed when annealed at magnetic field. The temperature coefficients of the remanence and coercivity were figured out. It was found that (1) the integrity of crystal was promoted;(2) the distribution of Nd-rich phase was improved;(3) the demagnetizing field and scattering field decreased;(4) the remanence and coercivity of the magnets were improved. The temperature coefficients were essentially the same at different temperatures in magnetic field. |
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