Understanding Disk Carbon Loss Kinetics for Heat Assisted Magnetic Recording

An optical pump-probe set-up that allowed short dwell time ( ~ 500 μs) heating with a high-temperature ramp rate ( ~ 10⁶ K/s) was used to detect the magnetization change in heat assisted magnetic recording (HAMR) media. The temperature of the media was monitored by observing the Kerr signal. The pump power at zero magnetization allowed the determination of the power needed to attain the Curie temperature of the media (the Curie temperature was determined with a high-temperature magnetometer before the pump-probe experiments). HAMR media was then irradiated with a pump power to obtain 480°C for increasing exposure times. Atomic force microscopy (AFM) of these media surfaces revealed depressions or holes in the media surface [within the carbon overcoat (COC) layer] that increased in extent with cumulative exposure time. Media surfaces exposed to somewhat lower temperatures (450°C) and for shorter times had a swollen region that surrounded a much smaller depression. High-spatial resolution Raman spectroscopy was used to analyze these irradiated areas. An increased D-band was observed within the swollen portion of the media surface, while the overall Raman signal intensity decreased within the small depressed area. Using time and temperature irradiations along with AFM analysis of the depressions the activation energy for COC loss was determined to be 0.6 eV. These observations were attributed to COC failure through graphitization and oxidation. The failure mechanism leading to these observed changes and the possible relationship of the present results to the HAMR media COC thermal stability are discussed.