Microwave absorbing properties of cobalt nanowires with transverse magnetocrystalline anisotropy

Abstract

Cobalt nanowires with c-axis perpendicular to the axial direction have been fabricated by the pulsed electrodeposition method. The hysterisis loops of the cobalt nanowire array show little anisotropy due to the competition between shape anisotropy and factors such as magnetocrystalline anisotropy and magnetostatic interaction. The permittivity and permeability dispersion spectra of the nanowire/paraffin composite were measured in the frequency range of 2—18 GHz. It was found that the imaginary part of the permittivity spectra shows a strong peak around 5 GHz and a weak peak around 10 GHz, which are contributed by the Debye relaxation and the conductivity of the nanowires. In the meantime, the imaginary part of the permeability spectra for the nanowire/paraffin composite samples exhibits a strong absorption peak at 6.1 GHz and two minor peaks above 10 GHz. The peak at 6.1 GHz is attributed to the natural resonance mechanism and the other two peaks are duc to eddy current effect. The permeability spectra attributed to natural resonance are fitted using the Landau–Lifshitz–Gilbert equation. Calculation based on the Kittel equation substantiates our fitting results. The electromagnetic wave reflection loss of the nanowire/paraffin composite sample is lower than -20 dB when the thickness of the nanowire/paraffin composite has been adjusted, suggesting that the cobalt nanowire composites can find application as a novel type of microwave absorbers.