The Synthesis And Properties Of The Barium Strontium Hexaferrite Nanopowder

Because of its high coercivity and saturation magnetization, uniaxial anisotropy,excellent chemical stability as well as low cost, M-type hexaferrite is widely used as highdensity magnetic recording materials, microwave absorption materials and microwave devices,et al.M-type barium strontium hexaferrite Ba0.5Sr0.5Fe12O19nanopowders were synthesizedsuccessfully via sol-gel auto-combustion method. Effects of the starting solution PH, the moleratio of citric acid and metallic ions (CA/M) and the addition ratio of ammonium nitrate (N)on the phases, morphology and magnetic properties of Ba0.5Sr0.5Fe12O19powders were studied.The influence of Ce3+ion-substitution on the absorption property of the ferrite was alsodiscussed in this paper. The phase composition, morphology and properties of the sampleswere characterized by the X-ray diffractometer (XRD), scanning electron microscope (SEM),vibrating sample magnetometer (VSM) and vector network analyzer (VNA). Main results ofthis study are as follows:(1) Changes of the starting solution PH have no obvious influences on the phasecomposition of the barium strontium hexaferrite. After heat-treatment, all products could beconsidered to be pure M-type BaSr hexaferrite phase. The grain size increases with theincreasing PH value. The VSM testing results show that the synthesized ferrite powders haveexcellent magnetic properties such as high coercivity, remanence and saturation magnetization,can be used as hard magnetic materials. Considered all the magnetic parameters comprehen-sively, the sample with best magnetic properties is gotten at PH=6, and its coercivity,remanence and saturation magnetization are4001.2Oe,39.104emu/g and62.806emu/g,respectively.(2) It can be learned from the XRD patterns that CA/M has great effect on thecomposition of products. When CA/M=0.54, there are considerable amounts of α-Fe2O3impurity phase in the product, and the purity is better with higher CA/M, and so is thedispersiveness. Products with CA/M≥1could be considered to be pure M-type BaSr hexaferrite phase. With increasing CA/M, the grain size increases first and then decreases, butall of them are in the nanoscale. When CA/M=1.2, the biggest grain size is97nm. Thehysteresis loops from magnetometer shows that phase purity has a great impact on themagnetic properties which are improved apparently when CA/M increases. When CA/M=1.5,the magnetic property is better than others, and its magnetic parameters are Hc=5207.6Oe,Mr=39.332emu/g and Ms=64.645emu/g, respectively.(3) When N=0.6, minor amounts of impurity phase α-Fe2O3were detected. The grainsize decreases with increasing N, and when N=0.6, the size is about84nm. It can be learnedfrom the hysteresis loops that the magnetic property reduces with increasing N. So theproduct with best magnetic property is gotten at N=0.2, and its Hc, Mr and Ms are5312.0Oe,37.786emu/g and61.848emu/g, respectively.(4) Doping cerium ions (Ce3+) could improve the absorbing ability of BaSr ferriteeffectively. When the Ce3+content is0.14(x=0.14), Ba0.5Sr0.5Ce0.14Fe11.86O19/paraffincomposite with the thickness of2.5mm, has the best absorbing properties. The maximumreflection loss reaches to-35.5dB at13.4GHz, and lower than-10dB (with absorptivity of90%) bandwidth reaches2.4GHz, which indicates that Ba0.5Sr0.5Ce0.14Fe11.86O19could beused as absorption materials.