Morphological and magnetic properties of carbon–nickel nanocomposite thin films

Carbon–nickel nanocomposite thin films were prepared by ion beam cosputtering a graphite target having a nickel chip attached to its surface. The amount of Ni incorporated in the films was controlled by the size of the Ni chip (from 5to22wt%), and measured by in situ x-ray photoelectron spectroscopy (XPS). High-resolution transmission electron microscopy images indicated that the films have a granular structure with nanosize Ni particles embedded in an amorphous carbon matrix. The Ni particles have an average radius of ∼2nm, with a rather narrow size distribution. Magnetization measurements revealed that films are superparamagnetic and present blocking temperatures TB<13K. The combined results of XPS and magnetic measurements indicate that Ni particles are free from oxide layers. In addition, the estimated value of their anisotropy constant was found to be higher than the expected value for bulk Ni. The origin of this discrepancy is associated with both shape and interaction anisotropies.