Laser Heating-Induced Degradation of Ultrathin Media Carbon Overcoat for 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. A tiny area of the magnetic recording media has to be heated up to a high temperature with a laser to lower the coercivity temporarily before information can be written on the area. The possible degradation of the ultrathin media carbon overcoat induced by the laser heating is a concern. In this paper, the laser heating-induced degradation of ultrathin a-C:Nx, a-C:Hx, and a-C overcoats on HAMR media is studied. Surface topography changes induced by the laser heating are evaluated with atomic force microscopy and structure changes with the visible Raman spectrum and X-ray photoelectron spectroscopy (XPS). Laser heating areas are analyzed with time-of-flight secondary ion mass spectrometry and XPS to reveal the underlying mechanism of the degradations. It is found that at a proper HAMR writing temperature and for a total laser heating duration corresponding to a five-year drive life, the surface topography, structure, and composition of the a-C:Nx overcoat are changed by the laser heating. However, the surface topographies of the a-C:Hx and a-C overcoats are not changed. The structure and composition of the a-C:Hx and a-C overcoats are also not changed much. Interlayer diffusion between the carbon overcoat and the underlying magnetic layer is confirmed in the laser heating area for all the three overcoats.