Raj Thangaraj

Influence of oxide on the structural and magnetic properties of CoPt alloy

Perpendicular recording media consisting of isolated CoPt magnetic grains separated with a nonmagnetic oxide grain boundary can be prepared by sputtering a Ru interlayer and then cosputtering CoPt with an oxide material, with low adatom mobility. The oxide material moves into the grain boundaries and isolates the magnetic grains. An increase in the oxide volume fraction in the magnetic layer does not affect the saturation magnetization but significantly reduces the magnetocrystalline anisotropy of magnetic grains. This may impose a limit on the areal density capability of this media design since media with smaller grains will require a larger oxide volume fraction that will reduce magnetocrystalline anisotropy of the CoPt based magnetic grains.

Ion beam deposition of carbon overcoats for magnetic thin film media

Ion beam deposited carbon has been investigated for its use as an overcoat for magnetic thin film media. By using a gridless end-Hall ion source, carbon has been deposited that possesses hardnesses to 18 GPa, stress to 4.5 GPa, and densities up to 2.6 g/cc. Contact-start-stop testing of ion beam deposited carbon to fifty thousand cycles shows a marked improvement in failure rate compared to hydrogenated and nitrogenated carbon. Energetic deposition of carbon thin films can lead to implantation of energetic species into the magnetic layer. Simulations have been performed to assess the vulnerability of the magnetic layer to energetic implantation of carbon. In addition, the effect of the partial pressure on the magnetic performance is assessed and a critical impurity concentration defined.

Growth Randomness, Porosity, and Surface Coverage of Carbon Films

Mathematical models that describe the static growth processes of sputtered and ion-beam deposited amorphous carbon films are established. Two important factors are considered in deriving the models: the film porosity and the growth randomness. The growth randomness for both hydrogenated sputter carbon and hydrogenated ion-beam carbon films are deduced from the film roughness vs. film thickness data obtained from X-ray reflectometry. The porosities of the two types of films are estimated from the experimentally determined values of film densities and sp3 /sp2 C–C bonding ratios. The derived film growth models, which find support from a surface coverage experiment, have allowed us to predict the surface coverage of the two types of carbon films in the thickness range of interest. We find that, neglecting intermixing at the substrate/carbon interface, the denser ion-beam carbon films are nearly as effective at achieving a similar level of surface coverage as the less dense sputter carbon films at twice the thicknesses. Our surface coverage model points to further increasing the carbon film density as the most effective approach for the continued reduction in the carbon overcoat thickness while maintaining adequate surface coverage.Copyright