Magnetic behaviour of composites containing polyaniline-coated manganese-zinc ferrite

Polycrystalline manganese-zinc ferrite has been coated with polyaniline (PANI) and embedded into a polyurethane matrix. The complex permeability of the composites was studied in the frequency range 1 MHz-3GHz. The conductivity of PANI coating was adjusted by controlled protonation with picric acid, Large shifts in the resonance frequency were observed as a function of varying PANI conductivity. The changes in the magnetic properties of the PANI-coated composite material are due to the change of the boundary conditions of the microwave field at the interface between the ferrite particle and polymer matrix. This effect is observed especially when the magnetic anisotropy of ferrite is low. (C) 2003 Elsevier B.V. All rights reserved.