Synthesis of single crystal and microwave characteristics of magnetoplumbite type Ferrite

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Microwave radiation in the GHz band is increasingly being used in many various communication devices. Magnetic resonance phenomenon is known to appear near the frequency of 48 GHz in hexagonal M-type ferrite or W-type ferrite. It has been studied that the substitution by metal such as Ti, Mn and so on for Fe^<3+> in BaFe_12O_19 caused the reduction of resonance frequency from about 50 GHz to less than 10 GHz. And then this ferrite was found to be used as microwave absorber or countermeasure to EMI(elecromagnetic compatibility). Furthrermore, single crystal ferrite which show the inheret properties of substance, has been synthesized in order to improve the absorber characteristics of hexagonal ferrite. Crystal growth has been carried out in two stage electric furnace by Bridgmann method. The mixture of Fe_2O_3 and BaCO_3 powders in according to the ratio of chemical formulaBaFe_12O_19 were pelletized and calcinated at 1300℃, and crushed to the size of a few μm and prepared for crystal g … More rowth. Powder was put into Pt crucible and heated to more than1450℃(m.p.). The melt was hold at 1450℃ and lowered down at 2-10mm/h (cooling rate :5-10 ℃/h) to 1250℃. After the whole melt soidified, the crucble was fall down into water and quenched. The surface of ingot was portioned with grain boundarys, like as honeycomb structure. Each hexagonal facet has metalic luster. These were cut off by a diamond cutter and analized by X-ray Laue photuograph. Each pieces were single crystals indicating hexagonal symmetry. These samples were cut pararelly to c-axis or c-face in hexagonal ferrite, and prepared for magnetic measurement by vsm. The saturation magnetization Ms and the coercive force iHc are 80 emu/g and 4kOe, respectively. Also these samples were formed to toroidal shape and measured microwave characteristics (complex permeability μ and permittivity ε) in the range of 1-20 GHz by a network analyzer. The magnetic resonance appear near 48GHz in Ba ferrite. Therefore the resonance frequency need to be controlled to the frequency range of 1-20 GHz, which are used for practical application. And then, the substitution of metal such as Ti, Mn, Sn and Zr for Fe^<3+> in Ba ferrite was carried out, to investigate the effects on the microwave characteristics. At present, sigle crystal of metal substituted Ba ferrite is being tried and synthesized. Less