Gigahertz range electromagnetic wave absorbers made of amorphous-carbon-based magnetic nanocomposites

Nanocomposite magnetic materials alpha-Fe/C(a), Fe2B/C(a), and Fe1.4Co0.6B/C(a) were prepared by mechanically grinding alpha-Fe, Fe2B, or Fe1.4Co0.6B with amorphous carbon [C(a)] powders. Complex permittivity, permeability, and electromagnetic wave absorption properties of resin compacts containing 40-vol % composite powders of alpha-Fe/C(a), Fe2B/C(a), and Fe1.4Co0.6B/C(a) were characterized according to a conventional reflection/transmission technique. The real part (epsilon(')(r)) and imaginary part (epsilon(')(r)) of the relative permittivity are low and almost independent of frequency between 0.05 and 40 GHz. The Imaginary part (mu(')(r)) of the relative permeability exhibited wide peaks in the 1-9-GHz range for alpha-Fe/C(a), in the 2-18-GHz range for Fe2B/C(a), and in the 18-40-GHz range for Fe1.4Co0.6B/C(a) owing to their different magnetocrystalline anisotropy field (H-A) values. Consequently, the resin compacts of 40-vol % alpha-Fe/C(a), Fe2B/C(a), and Fe1.4Co0.6B/C(a) powders provided good electromagnetic (em) wave absorption performances (reflection loss <-20 dB) in ranges of 4.3-8.2 GHz (G band), 7.5-16.0 GHz (X band), and 26.5-40 GHz (Q band) over absorber thicknesses of 1.8-3.3, 1.2-2.2, and 0.63-0.82 mm, respectively. Our experimental results demonstrate that the amorphous-carbon-based magnetic nanocomposites are promising for the application to produce thin and light EM wave absorbers. (c) 2005 American Institute of Physics.