Surface texture parameters of perpendicular recording magnetic disks

Because the flying height between a magnetic head and magnetic disk surface in hard disk storages is to be decreased to less than 1 nm, the head wear reliability due to intermittent asperity contacts and slider instability become critical issues. Nevertheless, detailed asperity characteristics of perpendicular magnetic disk have never been reported in open literatures. This paper presents the detailed features of surface texture parameters intrinsic to the perpendicular magnetic grains of commercially available magnetic disk drives (500 GB/platter), i.e., mean asperity height, asperity density, distance between the nearest asperities, radius of curvature of the asperities, and their histograms in addition to typical roughness parameters. It was found that mean asperity height is ～0.5 nm, asperity density ～5000 μm-2, nearest asperity distance ～11 nm. The asperity radius of curvature has an anisotropic nature, probably due to lubricant molecular conformation, but its averaged value is ～20 nm. Various parameter values of mountain and valley are also presented. On the basis of the measured roughness parameter values, the previous analytical results for the head-disk interface characteristics are reviewed.