Study of Lubricant Depletion Induced by Pulsed-Laser Irradiation Heating in Heat-Assisted Magnetic Recording

In this study, we experimentally investigated the lubricant depletion caused by pulsed-laser irradiation heating and discussed the fundamental characteristics, comparing it with the results obtained by continuous laser heating. As a result, it was found that the decrease in the lubricant depletion due to pulsed-laser heating was smaller than that to continuous laser heating and depended on an increase in the duty ratio as it increased. In addition, the lubricant depletion depends on the full width at half maximum (FWHM) of the temperature distribution due to pulsed-laser irradiation heating and increased as the FWHM increased. Therefore, it is also suggested that the lubricant depletion issue will not be so critical in actual HAMR systems because the FWHM would be very small.

Molecular Dynamics Simulation of Ultrathin Perfluoropolyether Lubricant Depletion under Moving Laser Heating

In this work, molecular dynamics simulations of nanostructured perfluoropolyether (PFPE) lubricants were performed to investigate the depletion instability under rapid scanning laser heating. A modified coarse-gained model was utilized to represent the random copolymer structures of PFPEs. In the simulation, only a partial lubricant near the substrate was irradiated by the laser beam to mimic the nano-scale heat transfer from disk to lubricant. During the laser heating, the surface morphological changes of the PFPE lubricant indicated that the lubricant beads initially raise up and diffuse due to thermal expansion, and then evaporate and form circular ridges around the laser beam center, leading to aggravated depletion. Moreover, the lubricant decomposition was subtle and regarded as negligible; while the raised ridges around the depletion area signified that the non-equilibrium thermo-capillary stress plays an important role in lubricant depletion. The surface temperature contour profiles of the lubricant were evaluated as well. It was showed that the increased temperature is centered around the laser beam and quickly decays toward the ambient temperature, forming non-concentric oval shape distributions and ultrahigh lateral thermal gradients. In addition, the maximum temperature (up to 990 K) was also examined and it is consistent with the ones required by HAMR systems to achieve areal densities beyond 1 Tb/in2.