Magnetic disk including protective layer having surface with protrusions, and substrate therefor

摘要

A magnetic disk includes a substrate, a magnetic layer, and a protective layer. At least one region of a surface of the magnetic disk has protrusions. A height of each of the protrusions is not less than 5 nm and not greater than 40 nm, and is within ±30% of an average height of the protrusions. A density of the protrusions is not less than 200/mm2 and is not greater than 250,000/mm2. A width of a surface of each of the protrusions in a radial direction of the magnetic disk is not less than 0.1 mum and is not greater than 10 mum. The protrusions are discrete protrusions aligned in a spiral direction of the magnetic disk at a predetermined spacing in the radial direction of the magnetic disk. The at least one region of the surface of the magnetic disk includes flat areas between the protrusions. At least some of the flat areas extend continuously from an inner redius of the at least one region of the surface of the magnetic disk to an outer radius of t he at least one region of the surface of the magnetic disk.