Magnetic and microwave properties of cobalt nanoplatelets

The Co nanoplatelets of 120 nm in diameter and 10 nm in thickness exist in both fcc and hcp crystal structures at room temperature. The saturation magnetization of the Co nanoplatelets is lower than that of the bulk Co because of the existence of the oxide layer. The coercivity is higher than that of the bulk Co. The equilibrium magnetic configuration of a single Co nanoplatelet without external magnetic field is a vortex structure, regardless of hcp or fee crystal structure. The Co nanoplatelets were coated by MnO2. The microwave properties of the MnO2-coated Co nanoplatelet composites and paraffin wax mixtures were measured in the 0.1-18 GHz frequency range. The complex permeability of the sample shows two broad resonance peaks and the complex permittivity of the sample shows one resonance peak in the frequency range of 0.1-18 GHz. The numerical simulations show that the reflection loss values of the MnO2-coated Co nanoplatelet composites and paraffin wax mixtures are less than - 12 dB in the 2-11.5 GHz frequency range. (C) 2007 Elsevier B.V. All rights reserved.