Cole-Cole impedance analysis on spin sprayed Ni-Zn-Co ferrite films exhibiting strong magnetic loss in gigahertz range

As the material for realizing gigahertz conducted noise suppressors, Ni-Zn-Co ferrite films (Ni_0.15-0.21Zn_0.20-0.36Co_xFe_2.39-2.58O₄, 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 f_r=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.