Structure and microwave characteristics of Co/TiO2 nanocomposites prepared by ball milling

Co/TiO2 nanocomposites were fabricated via direct ball milling. The structure and microwave characteristics of the Co/TiO2 nanocomposites were investigated. The results show that the hcp and fcc Co phases coexist in the nanocomposites for a long milling duration. The accumulation of the stacking faults in Co and the increase of the Co/TiO2 interfaces were detected by nuclear magnetic resonance. The measured relative complex permittivity of the ComTiO2 nanocomposite-paraffin wax mixture indicates that a high electrical resistivity and a dielectric loss exist in the Co/TiO2 nanocomposites. The dielectric loss mainly results from the polarisation of the metal/insulator interfaces. The imaginary part of the relative complex permeability of the mixture exhibits a broad resonance peak at 5.1 GHz which originates from the natural resonance in Co. The broadening of the resonance peak can be attributed to the fluctuating magnetocrystalline anisotropy at the stacking faults and interfaces regions. The calculated reflection loss curves show that the minimal reflection loss value of the Co/TiO2 nanocomposite-paraffin wax mixture can reach -32 dB at 4.0 GHz with a 3 mm sample thickness. The improved microwave absorption properties may result from the high electrical resistivity, dielectric loss and natural resonance.