Abstract

Cobalt ferrite (CoFe<inf>2</inf>O<inf>4</inf>) powders synthesised by sol-gel techniques were incorporated into natural rubber (NR) and polyurethane (PU) by two-roll milling at different loadings from 0 to 45 phr. In either NR or PU composites, the magnetisations were proportional to the CoFe <inf>2</inf>O<inf>4</inf> loading, but the coercive field remained rather insensitive to the loading. The frequency response from 1 MHz to 1 GHz revealed that the real part of the magnetic permeability increased significantly only in the case of 45 phr CoFe<inf>2</inf>O<inf>4</inf>, while the imaginary part was modest in both NR and PU composites. In contrast, the electrical permittivity of CoFe<inf>2</inf>O<inf>4</inf>-PU was larger than that of CoFe<inf>2</inf>O <inf>4</inf>-NR composites, and both parts at 100 MHz had linear variations with the loading, in agreement with Wagner's equation. © Institute of Materials, Minerals and Mining 2013.