Magnet Studies Of Planar Anisotropy Co₂Z Ferrite In Ultra-high Frequency Bands

Co₂Z-type ferrite with planar anisotropy is a promising material in UHF bands because of its high Curie temperature,high Q-factor,high permeability,high resonance frequency,it is widely used such as microwave devices,electromagnetic shileding and antenna materials.In the thesis,Co₂Z-type planar anisotropy ferrite powders were synthesized using two-step reaction method and molten salt method.The influence of different additives on the microstrcture and magnetic properties of the ferrite powders and sintered rings was investigated.It is a goal to obtain high resonance frequency in GHz band.The primary works are as follows:1.A series of M-type and Y-type ferrite powders were prepared by the molten salt method,and the optimal calcination temperature and Fe content were obtained.Then as-prepared M-type and Y-type ferrites were mixed at equal mole ratio,and a small amount of x wt% K₂CO₃（x = 0,0.2,0.4,0.6）was added in the mixture to synthesize Co2 Z ferrite powders and sintered rings.The powder showed the main Z-phase with plate shape.Ms decreased with increasing K₂CO₃ content slightly.At the same sintering temperature,the resonance frequency increased significantly and the intial permeability keep a relative high value and low loss obtained with increasing K₂CO₃ additive.The resonance frequency of adding 0.6 wt% K₂CO₃ sample is 1.2 GHz with tanδμ < 0.1 below 500 MHz,tanδε < 0.01 over 0.3-3 GHz at 1300℃ sintering temperature.2.Hexagonal ferrites powders and sintered rings of Co₂Z+0.6wt% K₂CO₃、Co₂Z+0.6wt% K₂CO₃+0.6wt% CuO、Co₂Z+0.6wt% K₂CO₃ +0.2wt% SnO2 and Co₂Z+0.6wt% K₂CO₃+0.6wt% SiO2 were synthesized by two-step reaction method.The powders showed hexagonl plate shape and the main Z-phase with minor W-phase at 1280℃ and 1300℃。The sample with SiO2 additive showed resonance frequency of 2.33 GHz with tanδμ < 0.15 below 500 MHz at 1300℃.All the samles have tanδμ < 0.03 over 0.3-3 GHz.3.Ba3Co1.6Fe24-xO41（x = 0.5,1,1.5,2.0）ferrite powders were were synthesized by molten salt method.The results showed hexagonal plate shape when calcined at 1280℃.The powders with x = 0.5 displayed optimal performance.Ba3Co1.6Fe23.5O41 and Ba1.5Sr1.5Co1.6Fe23.5O41 powders were synthesized by molten salt method.The calcined powders showed hexagonal plate shape.Composites sample were prepared by mixing magnetic powders and epoxy resin to achieve higher resonance frequency.It showed that Sr2+ substitution was beneficial to increase permeability of the composites.Two resonance peaks are observed for all samples.The resonance peak at 1.2-1.5 GHz is attributed to domain wall resonance,while the resonance peak at 4 GHz is attributed to natural resonance.Then composites with the fine powder were prepared again.The resonance peak from domain wall resonance nearly dissappeared and the resonance peak from natural resonance shifted to 6.4 GHz with real permeability of 3.