FMR investigations of iron-implanted polyethylene-terephthalate foils

Full text: Polyethylene-terephthalate (PET) foils were implanted with 40 keV Fe+ ions to fluences of (0.15-1.50) 1017 ions/cm2 at ion current density of 4 μA/cm2. The structure, surface morphology and composition of the modified PET foils were studied by atomic force microscopy (AFM), transmission electron microscopy (TEM) and dc resistivity measurements. AFM investigations showed formation of bumps on the polymer surface. The height, lateral size and density of the bumps increase with the implantation fluence. The TEM studies showed that the mean lateral size of iron nanoparticles for the PET films varies within 5-100 nm depending on the fluence. Areal density of the nanoparticles increases with the iron fluence. Good correlation between AFM and TEM images was found for the highest implantation fluence. Ferromagnetic resonance (FMR) technique was used to investigate the magnetic properties of the iron-implanted polyethylene-terephthalate films. The ferromagnetic resonance studies were performed using ESR spectrometer Bruker EMX series in X-band (9.5 GHz). FMR signals were observed for all as-prepared PET foils implanted with fluences higher than 0.15 1017 ions/cm2. Values of the effective magnetization were extracted from the dependencies of the FMR resonance fields on orientation. The FMR absorption intensities were estimated by numerical integration of the spectra. As a result, the plot of the effective magnetization and the signal intensity versus the implantation fluence were obtained for all PET samples in the dose range (0.25-1.50) 1017 ions/cm2. It was observed that the fluence dependence of the effective magnetization correlates well with that of the signal intensity. The percolation transition at implantation fluence of 1.0 1017 ions/cm2 is observed in both fluence dependencies. A minimum in the dc resistance found for the same fluence indicates that an exchange-mediated interaction rather than the dipolar one is underlying mechanism for the percolation transition observed in the FMR measurements. Formation of the carbonised layer as a result of the high-fluence implantation of the polymer may be responsible for electrical coupling of the magnetic granules. This research was supported by the grant No. FEN.YY.072/081004 of Research Fund of Marmara University, Turkey