Study Of Preparation Of SrFe₁₂O₁₉ And FeSiAl Anisotropic Magnets By Magnetic Orientation And Their Properties

With the fast development of science and technology,magnetic field has been more and more important in science researches and engineering.It is an effective route to align materials which are anisotropic magnetic for ordered structures with a magnetic field,so that the properties can be adjusted and improved.In this thesis,anisotropic magnetic composites made of hard magnetic Sr Fe₁₂O₁₉ particles with significant magnetocrystalline anisotropy and soft magnetic flaky Fe-Si-Al particles with significant shape anisotropy by magnetic orientation are studyed.The microstructures,magnetic and electromagnetic properties of the samples are investigated.The major results of this thesis are listed below:?1?Plate-like Sr Fe₁₂O₁₉ particles are hydrothermally synthesized.The optimum synthesis condition is identified as R_F/S 8:1,at 220?,5h.The hexagonal plate-like particles are about 75 nm in thickness and 2.3?m in diameter.The saturated magnetization?M_s?is about 51.4 emu/g,and the coercivity?H_c?is about 1171.6 Oe.Sr Fe₁₂O₁₉ composites with different structures are prepared by orientation of the plate-like Sr Fe₁₂O₁₉ particles in epoxy matrix.Sr Fe₁₂O₁₉ particles arrange with the plate perpendicular to the field direction after magnetic orientation.The remanence?M_r?and maximum energy products?BH?_max of the aligned samples are effectively adjusted.The perpendicular sample is better at storage capacity of electric and magnetic energy than the others.The parallel sample causes maximum dielectric loss and the perpendicular sample causes minimum dielectric loss in the frequency range 2-12 GHz and 14.4-18 GHz,while it is reverse in the frequency range 12-14.4 GHz.The nonaligned sample make maximum magnetic loss in the low frequency range,while the aligned samples are not good at magnetic loss in the whole frequency range.?2?Flaky Fe-Si-Al particles are obtained by ball milling with optimum process of 300 rpm,10 h and mass ratio of grinding media to material of 10/1.The flaky particles are about 500 nm in thickness and the internal stress enhances.The M_s reduces from 124.1 emu/g to 114.2 emu/g while H_c increases from 10.4 Oe to 30.1 Oe.Fe-Si-Al soft magnetic composites?SMCs?with different structures are prepared by orientation of the flaky Fe-Si-Al particles in epoxy matrix under a magnetic field.The effective permeability??_e?values of Fe-Si-Al SMCs are approximately constant from 25 k Hz to 125k Hz.Rotating-perpendicular sample owns the highest?_e value,while parallel sample owns the lowest?_e value.Rotating-parallel sample causes the lowest core loss(P_cv),while parallel sample causes the highest one.In a word,magnetic field can make order structures in hard and soft magnetic composites,so that the magnetic and electromagnetic properties can be adjusted and improved.These results are useful for preparation and application of anisotropic magnetic materials.