Patent ID: 8345376

Claim:
A magnetic disk device comprising: a magnetic disk having a non-magnetic substrate, a magnetic layer, a protection layer and a lubrication layer that are sequentially stacked in the stated order, a surface of the lubrication layer having a plurality of irregular structures disposed along a circumferential direction of the magnetic disk, each irregular structure having a circumferential length that corresponds to a respective central angle thereof, each irregular structure being positioned on the magnetic disk a distance away from the center of the magnetic disk in a radial direction corresponding to the central angle thereof, such that for irregular structures positioned the same distance away from said center, their central angles have the same value; a magnetic head slider that has a natural frequency of f and that magnetically records to the magnetic disk; and a motor that rotates the magnetic disk at a constant rotation speed R 0 , the distance of each irregular structure away from said center being in a range in which the magnetic head slider operates, the central angle of each irregular structure being different from an angle θ 0 expressed by the following equation: θ 0 =360×( R 0 /60)/( f× 1000).