The magnetic properties, especially the high frequency magnetic mechanism, of Ni-substituted CO(2)Z hexagonal ferrite were studied. The polycrystalline Z-type hexagonal ferrite of Ba3NixCO2-xFe24O41 (0 <= x <= 2) were prepared by solid-state reaction. The results indicate that Ni-substituted Co(2)Z samples all exhibit typical soft magnetic character. Substitution of Ni for Co will turn the planar magnetocrystalline anisotropy of CO(2)Z to uniaxial anisotropy when x >= 1, so that the permeability drops dramatically and domain wall resonance appears in the frequency spectra. With the rise of Ni amount or sintering temperature, domain wall resonance strengthens gradually. (C) 2008 Elsevier Ltd. All rights reserved.