Nanomechanical and nanotribological characterization of nanometer ultra-thin composite films

Youfeng Zhang¹, Ahmad S. Shakil², Hongbo Wang³, Xinwei Li³, Huan Tang³, Andreas A. Polycarpou²

¹Headway Technologies, 682 South Hillview Drive, Milpitas, CA 95035, USA

²Department of Mechanical Engineering, Texas A&M University, College Station, TX 77840, USA

³Seagate Technology LLC, 47488 Kato Road, Fremont, CA 94538, USA

ABSTRACT: Perpendicular magnetic recording disks consist of an ultra-thin (of the order of 10 nm) CoCrPt-SiO₂ composite layer as the data storage medium. CoCrPt is distributed as grains in magnetic media whereas SiO₂ acts as grain boundaries. Proportion of grain boundaries in the media is termed as grain boundary fraction. Scratch induced demagnetization is a major failure mechanism for the material and thus investigation of the media layer’s mechanical and tribological properties is important. In this work, three different magnetic disk samples were deposited using different sputtering bias voltages, which affect their grain boundary fractions. Shallow nanoindentation experiments have been performed on the sample to directly measure the mechanical properties of the composite films. The results reveal clear dependence on their grain boundary fractions. Hardness, elastic modulus, yield strength and Poisson’s ratio of the samples decrease with increase in grain boundary fraction of the media. Nanoscratch experiments were also performed to obtain the friction and wear properties of the media samples. In situ and residual scratch depths have been measured in these experiments. It has been found that in-situ scratch depths include mainly elastic deformation and are more dependent on the elastic modulus of the substrate. The COF values of the samples are similar because of the similarity of their in-situ scratch depths. The wear rate calculated from the nanoscratch experiments shows that the higher the grain boundary fraction, the higher the wear rate.