Fabrication and Electromagnetic wave absorption Properties of Co-Cu-substituted Ni-Zn Spinel Ferrite-epoxy Composites

Abstract

Spinel ferrites (Ni0.5Zn0.5)1-<i>x-y</i>Co<i>x</i>Cu<i>y</i>Fe2O4, (<i>x</i> = 0 and <i>y</i> = 0, <i>x</i> = 0.2 and <i>y</i> = 0, <i>x</i> = 0.1 and <i>y</i> = 0.1, <i>x</i> = 0 and <i>y</i> = 0.2) were prepared by sol-gel method and post-annealed at 1100 ^oC. The grain growth of the sample is very sensitive to the Cu substitution <i>y</i>. The average grain size of the non-doped sample (<i>x</i> = 0, <i>y</i> = 0) was ~400 nm and it increased to ~3 μm at the sample with <i>x</i> = 0 and <i>y</i> = 0.2. The real and imaginary parts of permittivities (<i>ε', ε"</i>) and permeabilities (<i>μ', μ"</i>) were measured on the spinel ferrite powder-epoxy (10 wt%) composite samples by a network vector analyzer in the frequency range of 0.1 ≤ <i>f</i> ≤ 15 GHz. The <i>μ'</i> and <i>μ"</i> depend on Co substitution <i>x</i> and the <i>ε'</i> is sensitive to Cu doping <i>y</i>. 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 (<i>d</i>) and frequency (<i>f</i>), 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 <i>x</i> = 0.1 and <i>y</i> = 0.1, <i>x</i> = 0.2 and <i>y</i> = 0 also exhibited a very broad-ranged EM wave absorbing performance with a <i>d</i> < 3 mm, indicated by RL < -10 dB being satisfied in the frequency range 7~14 GHz.