Effect of Functional End-Groups on Lubricant Reflow in Heat-Assisted Magnetic Recording (HAMR)

In the developing heat-assisted magnetic recording technology, a laser heats up the magnetic media to the Curie temperature of a few hundred degrees celsius for a few nanoseconds. Accordingly, the thin-film lubricant coating on the disk experiences thermo-capillary and evaporation effects followed by its depletion. In order to maintain a reliable head–disk interface, the lubricant needs to return to the initial uniform profile, in a process known as lubricant reflow. We performed numerical simulations of the lubricant reflow and compared the recovery times for widely used lubricants in hard disk industry including Z-dol, Z-tetraol, and ZTMD lubricants with similar molecular weights. We modeled the lubricant reflow on the disk for a wide range of film thicknesses and laser spot sizes, based on a classical lubrication theory and material properties reported by experiments. The results show that the recovery times for Z-tetraol 2200 and ZTMD are significantly greater than that for Z-dol 2000, while the recovery time for ZTMD is close to that for Z-tetraol, despite its higher viscosity value. It is also shown that all lubricants have an optimum film thickness for recovery time, and this optimum point largely depends on the dewetting behavior of the lubricant.