Magnetic and dielectric properties of natural rubber and polyurethane composites filled with cobalt ferrite

Abstract

Cobalt ferrite (CoFe2O4) 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 CoFe2O4 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 CoFe2O4, while the imaginary part was modest in both NR and PU composites. In contrast, the electrical permittivity of CoFe2O4–PU was larger than that of CoFe2O4–NR composites, and both parts at 100 MHz had linear variations with the loading, in agreement with Wagner’s equation.