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As the material for realizing gigahertz conducted noise suppressors, Ni-Zn-Co ferrite films (Ni0.15-0.21Zn0.20-0.36CoxFe2.39-2.58O4, x=0-0.10) were deposited from an aqueous solution by spin spray ferrite plating at 90°C. We applied 1.3-kOe bias field parallel to the centrifugal direction of liquid flow on the substrate. The bias field and the Co addition induced an in-plane uniaxial anisotropy with easy axis parallel to the liquid flow (or bias field) direction. The effect was strongest at x=0.03; the complex permeability (μ=μ'-jμ'') along the hard axis exhibited a high-natural ferromagnetic resonance of fr=1.4 GHz and a strong magnetic loss of μ''>30 in a wide range between 300 MHz and 3 GHz. Measured along the easy axis, however, μ' and μ'' were negligibly small, indicating that the high permeability with strong loss was ascribed to magnetization rotation, with no contribution from domain motion. Cole-Cole impedance (0.1 Hz-1 MHz) plots for each Ni-Zn-Co ferrite film were fitted by a depressed semicircle, whose relaxation angle became largest at x=0.03. This means that the relaxation time in conduction process is most widely dispersed at the same Co content where, as mentioned above, the magnetic loss became strong in a wide frequency range.
Date of Publication: Sept. 2003