Laser-Induced Thermo-Desorption of Perfluoropolyether Lubricant from the Surface of a Heat-Assisted Magnetic Recording Disk: Lubricant Evaporation and Diffusion

Abstract

Heat-assisted magnetic recording (HAMR) storage technology will thermally stress the lubricant film typically applied to the storage disk surface. Different lubricant loss and morphology change mechanisms have been hypothesized to occur during information writing. A loss to of the lubricant film will dramatically affect its overall mechanical and chemical performance of the head–disk interface, decreasing its reliability and its durability. Thus an all optical pump–probe method was used to study the effect of fast thermal transients (106 K/s) on a lubricant film on HAMR media. Thermal transients (Bhushan and Cheng in J Appl Phys 81:5390, 1997) with peak temperatures above the HAMR media Curie temperature (T c) were found to remove by evaporation the lubricant within the heated region creating a lubricant depression in the otherwise continuous film. No accumulation of lubricant volume was observed to take place in the cooler regions of the thermal spot, indicating that thermocapillary shear stress is not an important mechanism of lubricant thickness change with the optical spot size used (65 μm). The onset of lubricant loss was observed to begin at approximately 610 K and was totally removed at 823 K. The change in depth of the lubricant depression with time showed that no structural terms contributed to the disjoining pressure for the lubricant thickness range studied. From this change, the diffusion coefficient of the lubricant on the carbon overcoat surface was determined to be 1 × 10−13 m2/s by fitting Fick’s second law to the normalized lubricant thickness. The importance of these observations on the operating HAMR head–disk interface is discussed.