Control of high-frequency permeability in polycrystalline (Ba,Co)-Z-type hexagonal ferrite

Polycrystalline Z-type hexagonal ferrites were prepared by an usual ceramic sintering method, where a part of Ba ions were replaced by Sr ions and a small amount of SiO2 was added. The complex permeability spectra of each were measured. The low-frequency permeability increased until a half of Ba ions were substituted by Sr ions, and the natural resonance frequency remained almost constant and was almost insensitive to the substitution. On further substitution, the permeability remarkably decreased. This tendency indicated the enhancement of the Snoek's product. As the adding amount of SiO2 was increased, the low-frequency permeability decreased and the natural resonance frequency shifted toward higher frequency. These spectral variations were easily understood within the magnetic circuit model. From these results, it was possible to fabricate the polycrystalline hexagonal ferrite with the controlled complex permeability, which was suitable to the improvement in the antenna performance of hand-held cellular telephones. (C) 2002 Elsevier Science B.V. All rights reserved.