Co_2Z is a planar hexagonal ferrite that exhibits a high permeability and ferromagnetic resonance up to the GHz region. It can be applied to components such as notebook, cellular phone etc. We noticed an effect of substitution of rare-earth metal ions for Co_2Z ferrite, which was not reported yet. Ba_3Co_2R_xFe_(24-x)O_(41) (R=La, Nd, Gd, Dy, Ho, Yb and x=0-0.5) samples with Z-type structure were prepared by the conventional ceramic method. The frequency dependence of initial permeability of all samples was measured from 0.01 to 1.8 GHz. The initial permeability (at 0.1 GHz) was higher than that of the Co_2Z ferrite without substitution. However, the initial permeability of the La~(3+) ion substituted sample decreased. In particular, the initial permeability of Gd~(3+) substituted Z-type ferrite sample (x=0.1) was the highest of all samples. The crystal structure of Ba_3Co_2R_xFe_(24-x)O_(41) (x=0.1) was single-phase Z-type structure. As a result, rare-earth ions formed a solid solution of Co_2Z ferrite. The measurement of the lattice constant for the x=0 and x=0.1 samples indicated that La ions substituted for Ba ions, and Gd, Dy, Ho and Yb ions substituted for Fe ions. The apparent specific anisotropy field H_A of a Gd~(3+) substituted Z-type ferrite sample (x=0.1) was the lowest of the series Ba_3Co_2R_xFe_(24-x)O_(41) (x=0, 0.1) samples.
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