Laser-Heating-Induced Damage to Ultrathin Carbon Overcoat in Heat-Assisted Magnetic Recording

Heat-assisted magnetic recording (HAMR) is a technique for overcoming the superparamagnetic limit and enabling large increases in the storage density of hard disk drives. The performance of the disk carbon overcoat under the high temperature in the heating-assisted writing process is a concern. Laser heating in HAMR is quite different from conventional slow heating. Laser heating temperature and total laser heating duration over the lifetime of the drive are two dominant factors in the experimental study of laser-heating-induced damage to the carbon overcoat, which must be carefully controlled. In this study, a rough estimation of the total laser heating time for a given point on the media over the 5-year lifetime of the drive is given. It is expected to be only 0.1 ms. The methods of controlling laser heating temperature and total laser heating time in experimental studies are explained in detail. Laser-heating-induced damage to the a-C:Nx and a-C:Hx overcoats on HAMR media are studied. Surface topographical changes caused by the laser heating are evaluated with atomic force microscopy and structure changes by visible Raman spectroscopy. It is found that laser heating induces surface topographical and structure changes, especially for the a-C:Nx overcoat.