Magnetoresistive effect and impedance spectroscopy of Co-implanted polyimide

Electronic properties and magnetoresistance of polyimide (PI) films implanted by 40 keV Co+ ions with high fluences at various ion current densities are studied. Insulator‐to‐metal transition (IMT) is found for the highest implantation fluence (1.25 × 1017 cm–2) at ion current densities of 8 and 12 µA/cm2. The IMT is caused by the radiation‐induced alteration of the implanted PI and agglomeration of the Co nanoparticles (NPs) providing an efficient percolation way for the charge carriers. Impedance spectroscopy shows the increase in capacitance with fluence for the samples on the dielectric side of the IMT, which is caused by formation of the conductive metal NPs and carbonised clusters separated by insulating polymer media. The percolation of the conductive phase for the samples on the metallic side of the IMT results in an inductive character of the impedance. The magnotoresistive effect is found to be positive for the samples on the dielectric side of the IMT and negative for the samples on the metallic side. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)