Scratch-Induced Demagnetization of Perpendicular Magnetic Disk

The mechanism of scratch-induced demagnetization was studied in perpendicular magnetic recording (PMR) disks. These scratches, which may occur on the disk´s surface during head/disk contact, cause demagnetization that results in read/write errors. The scratch-induced demagnetization is thus investigated by the scratch test, observation of atomic force microscopy and magnetic force microscopy, and analysis of transmission electronic microscopy. It was found that the angle of the grain in the recording layer, which is vertically orientated on a PMR disk, was tilted under the scratch. These analyses revealed that scratch-induced demagnetization is caused mainly by plastic deformation which results in grain tilt in the recording layer, rather than by stress. Therefore, a dense and not-easily titled grain structure in the recording layer is needed to produce a reliable hard disk drive (HDD).