Interface reactions between quaternary cobalt alloys and carbon coating inthin film disk media

A study of interface reactions between the magnetic layer and the protectiv e carbon coating, and the influence of these interactions on magnetic prope rties of rigid disk media for magnetic data storage is presented. Quaternar y CoPtCrB and CoPtCrTa alloy films and protective hydrogenated or nitrogena ted carbon coatings were deposited by dc magnetron sputtering onto metal ha rd disks (AlMg substrate/electroplated NiP layer/Cr underlayer). Core level x-ray photoelectron spectroscopy of nitrogenated carbon films on B-contain ing alloys showed the formation of boron nitride and small amounts of chrom ium nitride at the interface, and also indicated the likely presence of chr omium carbide. The amount of boron nitride at the interface varied dependin g on substrate bias voltage and temperature during deposition of the carbon coating. From a quantitative analysis of the x-ray photoelectron spectra i t was inferred that boron nitride formation was controlled by the diffusion of boron from deeper regions of the magnetic layer to the interface. Surpr isingly, compared to disks using the same magnetic alloy but with a hydroge nated or pure carbon coating, no effects of these interface reactions on th e magnetic properties of the disks could be detected. In contrast, for a Ta -containing alloy the same comparison revealed a drop in the coercivity of up to 200 Oe in disks with nitrogenated carbon overcoats. Strong evidence f or the formation of tantalum nitride as well as small amounts of chromium n itride was found in the photoelectron spectra. Thus, while the formation of boron nitride at the interface of CoPtCrB media and protective carbon coat ing does not affect the magnetic properties of the disks in the range of bo ron and nitrogen concentrations investigated here, small changes in the che mical environment of Ta and/or Cr can lead to significant changes in the ma gnetic properties of the CoPtCrTa media. (C) 2000 American Institute of Phy sics. [S0021-8979(00)00606-X].