Doping effect of multiwall carbon nanotubes on the microwave electromagnetic properties of NiCoZn spinel ferrites

NiCoZn ferrites have been found exhibiting two well separated resonance peaks. One is due to domain wall movement at 1.76 GHz. One is due to spin rotation at 6.80 GHz. With increasing the content of multiwall carbon nanotubes (MWCNTs) in the NiCoZn ferrite/MWCNT/wax hybrid composites, both resonance peaks are maintained, but their peak positions are found dependent on the MWCNT content. The damping factor for spin rotation is found decreasing as the content of MWCNT in composites increases. The dielectric loss of hybrid composites is also found significantly increased by increasing the content of MWCNT. The doping effects of MWCNT are thought due to the interaction between the ferrite and MWCNT. The microwave permeability of pure MWCNT has also been investigated, and it is believed due to the residual nanosized Ni particles.