| Abstract |
| Spinel ferrites (Ni0.5Zn0.5)1-x-yCoxCuyFe2O4, (x = 0 and y = 0, x = 0.2 and y = 0, x = 0.1 and y = 0.1, x = 0 and y = 0.2) were prepared by sol-gel method and post-annealed at 1100℃. The grain growth of the sample is very sensitive to the Cu substitution y. The average grain size of the non-doped sample (x = 0, y = 0) was ~400 nm and it increased to ~3 μm at the sample with x = 0 and y = 0.2. The real and imaginary parts of permittivities (ε', ε") and permeabilities (μ', μ") were measured on the spinel ferrite powder-epoxy (10 wt%) composite samples by a network vector analyzer in the frequency range of 0.1 ≤ f ≤ 15 GHz. The μ' and μ" depend on Co substitution x and the ε' is sensitive to Cu doping y. Reflection loss (RL), which implies electromagnetic (EM) wave absorption properties, were analyzed based on the complex permeability, permittivity spectra. In the RL map plotted as functions of sample thickness (d) and frequency (f), the intensive EM absorbing area (RL < -30 dB) shifted to a high frequency region with increasing Co substitution. This can be attributed to a permeability spectra shift, due to the increase in ferromagnetic resonance frequency produced by the Co substitution. The samples with x = 0.1 and y = 0.1, x = 0.2 and y = 0 also exhibited a very broad-ranged EM wave absorbing performance with a d < 3 mm, indicated by RL < -10 dB being satisfied in the frequency range 7~14 GHz.
(Received September 8, 2020; Accepted October 18, 2020) |
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| Key Words |
| Ni-Zn ferrites, permittivity, permeability, Reflection loss, EM absorption |
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