Study On The Synthesis And Magnetic Properties Of Nanometer Barium Ferrites Material

Abstract:Barium ferrite is a very important functional material for its magnetic properties, which is widely applied to the electrommunication, automatization, informatization, denfence, etc. In this paper, the pure and two kinds of substituted M-type Barium ferrites(Fe ions were substituted by Ti/Co or La ions) were synthesized by sol-gel auto combustion, and we used two types of thermal treatment methods in the annealing step including the traditional sintering and the new microwave sintering. The microstructure and the magnetic properties of the samples were studied by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and vibrating sample magnetometer (VSM) of the physical property measurement system (PPMS-9T).All the research details and results are as follows:(1) The M-type barium ferrites were synthesized by two different sintering ways. The results showed that the higher the annealing temperature is, the better the degree of crystallinity will be. Both raising the annealing temperature and prolonging the soaking time can increase the size of the sample particles. In the traditional sintering process, the saturation magnetization (Ms) is always increasing when the annealing temperature raises or the soaking time is prolonged, while the coercivity (HC) increases at first and then decreases. As the temperature raises and the soaking time is prolonged, the Ms and HC of the microwave sintering process changes as the trend of the Ms and HC in the traditional one. In the microwave sintering process, the maximum of Ms is69.2emu/g; the maximum and minimum of HC is5406,2410Oe. Compared with the traditional sintering method, the microwave sintering can improve the reactivity of the raw so that the degree of crystallinity becomes better although the soaking time is shortened. The improvement of crystallinity brings about the HC changes more rapidly and the Ms becomes much higher.(2) Ti/Co co-substituted and La substituted M-type barium ferrites were synthesized with the traditional sintering method. The results show that the substitution has not affect the crystal structure obviously; the microstructures and the particle sizes of the substituted samples annealed at the same temperature are the same. The magnetic test data indicate that the magnetic properties are affected by the substitution:with the increasing of Ti/Co co-substituting amount, the Ms decreases slightly (64.4-51.7emu/g), while the Hc changes much more (5274-52Oe); with the increasing of La substituting amount, the Ms decreases much more (64.48-43.48emu/g) and the Hc changes a little (5873.8-5293.5Oe). The reasons for the variety of magnetic properties are that the superexchange interaction and magnetocrystalline anisotropy field which are affected by the site preference of substituting ions, and the lattice distortion caused by the substitution.