Temperature-Induced Changes in the Optical and Material Characteristics of HAMR Media COC and Its Effect on Recording Performance

The carbon overcoat (COC) on heat-assisted magnetic recording (HAMR) media was deposited at increasing temperature. The optical extinction (k) of this media was measured with ellipsometry and found to increase with temperature from 0.2 to 0.9 over the temperature range from 220 °C to 360 °C. Raman spectroscopy of these COC surfaces had an increasing G-peak position and decreasing G-peak width along with an increasing I(D)/I(G). An increasing sp² ring/chain and aromatic cluster size and decreasing optical gap were inferred from these changing parameters. HAMR writing on this media was found to require incrementally less laser power (from 100% to 92%) with increasing optical extinction to attain a fixed track width. This was determined to be due to the increased imaginary component of the dielectric function in this film (2nk). The SNR of these written tracks was observed to improve by approximately 0.65 dB with deposition temperature. A finite-element method model of the head and media showed that the thermal gradient of the hot spot in the media increases with optical extinction and increases the SNR. A small decrease in the COC density with temperature was observed and was calculated to further decrease the COC thermal conductivity and thus enhance the increased thermal gradient.