The Research On The Preparation And Microwave Absorption Properties Of Ni�Co Nanoferrites

As a typical ferromagnetic material, ferrites have been deeply investigated by many researchers, especially its magnetism properties. They had a very wide range of applications in data recording, signal propagation, digital communications and the other fields, but there were still many difficulties when used at a high frequency as the absorbing materials. An �ideal� microwave absorbing material should have such advantages like light weight, wide bandwidth, low density, tiny thickness and low cost.So we invented a new method to prepare the Ni Co ferrites to improve the magnetism and microwave absorption properties.Firstly, we investigated the influence of preparation methods to the ferrites.Nickel�cobalt-oxide and iron powder were used as the raw materials to prepare Nix Co1-x Fe2O4 with different Ni/Co ratios(x = 0.2, 0.5, 0.8) by the method of microwave assisted ball milling, Stirred ball mill, pure microwave radiation and planetary ball milling. We found that only microwave-assisted ball milling could synthesize the aimed materials, but the other three kinds of methods can not compound it without the follow-up treatment(such as high temperature annealing, sintering). Combined with the Scherrer formula and JIADE analysis, we found the average size of particles is15 nm, and the lattice strain is about 0.2%.Then we carried out a further study by transmission electron microscope to investigate the structure and morphology of the target material. From the TEM and SAED pictures we found that the average size of grains is about 15 nm and proved the above-mentioned conclusion again. In addition, there were a large amount of clusters observed in the pictures which lately proved have much connection with the magnetic properties.One of the most important property of ferrite is magnetism, so we also analyzed the saturation magnetization, coercive force and the net magnetic moment. From the results we knew that the magnetic properties had a regular change with the increasing of nickel element. The phenomenon which was proved had a close relationship with the ions occupying. Then the morphology, magnetic and some other related properties of nickel and cobalt ferrite were investigated by adding the rare earth element Nd, and we found that the morphology and magnetic properties had a regular trend with the increase of Nd content.At last, We discussed the relative dielectric constant and relative permeabilityand their variable values with the change of frequency and thickness. At last, the following regulars were found by calculating the reflection values in the different thickness and frequency:(1) the real and imaginary parts of permittivity and permeability presented upward trend with increasing nickel content;(2) as the film thickness increases(in the range of 1�2.5 mm), the frequency values of the minimum reflection loss move left. Besides, the RL values of Ni0.5Co0.5Fe2O4 could reach-10 d B in the frequency of 6-15 GH, and the Ni0.8Co0.2Fe2O4 with a thickness of 2.5 mm could achieve-36.2 d B(99.99% absorption) at 11.52 GHz, which indicated that the Ni�Co nanoparticles possessed great potential in microwave absorption applications.