| With the rapid development of the modern industry and technology, the humankind has entered a flourish period with the application of the new technology. Electronic products have already been applied to the daily life of people, especially with the increasing popularization of home appliances, communication equipment and data-processing devices, the electromagnetic wave radiation becomes more and more serious and will become the problem people are popularly concerned about. The electromagnetic wave radiation turns into an important environment pollution after the water and air pollution, and it does great harm to the humankind. So the absorbing material has important implications in the field of radar and electromagnetic compatibility and it is very necessary to find a fine microwave absorbing material. Currently in this field people are interested in the use of the hexagonal ferrite-based microwave absorber to act as an absorbing material and provide absorption over a wide bandwidth. Ferrite is a very important class of magnetic material; more especially it is a metal oxide, which contains magnetic ions arranged in such a manner that it produces spontaneous magnetization while maintaining good dielectric and magnetic properties. The hexagonal-type ferrite absorbs microwave energy by lossy interaction of the magnetic field of the wave with their individual magnetization. The hexagonal ferrite materials are suitable for absorbing materials due to a significant value of permeability, low value of coercivity and planar anisotropic behavior in microwave frequencies. There are several types of hexagonal ferrites denoted as M, W and Y phases having complex crystal and magnetic structures. The Ba ion can be removed by rare earth ions and the magnetization was reported to be decreased with increasing amount of the substitution of rare earth ions. The presence of barium ion and the slightly peculiar structure causes the barium hexaferrite to have high magnetic and microwave absorbing properties unlike spinel and garnet.Notwithstanding, the magnetic anisotropy, the magnetic and microwaveabsorbing properties of the barium hexagonal ferrite can be further improved by the external doping a certain amount of rare earth ions (La, Nd, Sm).Firstly, the new preparation technique of the W-type hexagonal ferrite has been investigated in this chapter, and the W-type hexagonal ferrite samples have been prepared by the well-known solid state reaction method. By means of many experiments, finally it is found that the samples were sintered at 1250 for 3 h may as well. A series of rare earth ferrite samples of Ba,.RECoFeO with RE = La, Nd, Sm and x =0. 00, 0. 05, 0. 10, 0. 15, 0. 20, 0. 25, 0. 30, were also prepared by a solid state reaction method. Then the structures of the synthesized samples doped with rare earth ions were observed by X-ray diffraction, and the maximum of the doped coefficient x is 0. 20, 0. 25 and 0. 25 respectively, on condition that the structures of the rare earth W-type hexagonal ferrites have no any change.Secondly, magnetic measurements of the samples were carried out by the magnetic detector, and it is found that the substitution of a certain amount of the rare earth ions in the W-type hexagonal ferrites have no distinct effect on magnetic properties under the condition of unchanging their structures at all times, therefore the shape of the hysteresis curves also has no any change. On the contrary, if the structure of the W-type hexagonal ferrite changes due to the doped rare earth ions, accordingly, the parameters of its magnetic characteristics such as magnetization, retentivity and coercivity were also various prominently. So it has been found that the magnetic properties of the W-type hexagonal ferrites have a great connection with the interior structure of the ferrites.Finally, microwave absorbing properties of the synthesized samples have been described in the end of the paper. By analyzing the relation of the absorbing wave parameters (complex permittivitty and complex magnetic perme...
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