X-ray spectroscopic and magnetic investigation of C : Ni nanocomposite films grown by ion beam cosputtering

Abstract

The nearest-neighbor coordination and electronic structure in C:Ni(similar to 30 at.%) nanocomposite films grown by ion beam cosputtering in the temperature range of room temperatue (RT) to 500 degrees C are investigated by the means of extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge spectroscopy (XANES) and X-ray photoelectron spectroscopy (XPS). The obtained results are correlated with the composite nanostructure published elsewhere and magnetic properties determined by the means of X-ray magnetic circular dichroism (XMCD) and superconducting quantum interference device (SQUID) magnetometry. A combined use of EXAFS, XANES, and XPS shows that a carbidic Ni phase exhibiting only local atomic ordering is formed at low growth temperatures (<= 200 degrees C), while ordered carbidic Ni phase forms at similar to 300 degrees C. Further increase in growth temperature results in the formation of face-centered cubic (fee) Ni with a high degree of crystallinity. On the other hand, Ni incorporation strongly promotes the formation of carbon structures with the prominent peak in C K-edge XANES spectra positioned at 288.5 eV in the whole growth temperature range. The magnetic measurements show no magnetic response for the films grown at RT to 200 degrees C, superparamagnetic behavior for the film grown at 500 degrees C with >90% of the Ni atoms in metallic state, and a weak magnetic response for the film grown at 300 degrees C, indicating the presence of Ni-rich regions within carbon containing Ni nanoparticles with similar to 3% of Ni atoms in metallic state.