Life estimation of carbon overcoat on magnetic media for heatassisted magnetic recording using novel Raman spectroscopy

A heat-assisted magnetic recording (HAMR) is expected for a future high density recording of a hard disk drive. However, a carbon overcoat (COC) composed of diamond-like carbon (DLC) or a lubricant film is possibly damaged when a magnetic medium, i.e. CoPt alloy, is heated at around Curie temperature (Tc) of 600K by a near-field HAMR head. We carried out HAMR simulation experiments by using newly developed Raman spectroscopic systems, composed of plasmonic sensors for surface-enhanced Raman scattering (SERS), a pulsed laser heating, and an in-situ temperature measurement with an intensity ratio of anti-Stokes/Stokes lines. It was found that the heated temperature of the COC is higher than that of the magnetic film, i.e., 580°C and 366°C, respectively. Intensity changes of G-band peak in Raman spectra for DLC films were observed during the pulsed laser heating. The Raman intensity was exponentially decreased by oxidation in air, where time constants were calculated as a parameter of a pulse width. Degradation life of the DLC film can be estimated from a critical pulse width, where the time constant is extrapolated to zero. The estimated pulse width for no degradation was 250μs at the heating temperature of 580°C. The result shows no damage can be estimated in DLC films for HAMR because the effective irradiation time is 5ns and the accumulated irradiation time is 0.5ms in HAMR operations.