Magnetoresistive effect in PET films with iron nanoparticles synthesised by ion implantation

Thin polyethyleneterephthalate (PET) layers with Fe nanoparticles (NPs) were synthesised by high-fluence ion implantation. Temperature dependence of conductance and magnetoresitance were studied as a function of ion fluence. It is found that the implantation with fluences of about 1.0×1017 cm-2 causes high enough concentration of metal inclusions to provide conditions for electrical percolation that leads to an insulator-to-metal transition (IMT) in charge carrier transport mechanisms. The magnetoresistance measurements indicate that the magnetic percolation takes place at metal concentrations (fluences) lower than those needed for the electrical percolation. For the samples on insulating side of the IMT, a non-monotonous dependence of resistance in an increasing external magnetic field is observed due to anisotropic magnetoresistive effect and charge carrier scattering on magnetic inclusions. For the samples implanted with fluences > 1.0×1017 cm-2, the magnetoresistance becomes a monotonous decreasing function of the external magnetic field which is typical for ferromagnetic metals that indicates effective magnetic coupling of the iron inclusions.