Experimental Study of Lubricant Depletion in Heat Assisted Magnetic Recording

Heat assisted magnetic recording (HAMR) is a promising choice to overcome the superparamagnetic limit in magnetic recording and further increase the areal recoding density of a hard disk drive. However, HAMR brings about serious lubricant depletion problems on the disk surface due to the high temperature in the heat assisted writing process. Experimental studies of the lubricant depletion under HAMR conditions are still very limited so far. It is essential to do experimental studies under real HAMR conditions or under equivalent conditions if a stand-alone laser is used to emulate the HAMR system. In this work, a self-developed HAMR tester is introduced. A method to control the repeatability of laser heating temperature is explained. Lubricant depletion, accumulation, loss, the percentage of accumulation to depletion, and the depth of depletion are determined quantitatively. The effects of laser power, total laser-on-time and laser-off-time in one laser heating and cooling cycle on lubricant depletion are studied experimentally with the HAMR tester. From the experimental studies, it is found that lubricant accumulation at the edge of the lubricant depletion track takes a considerable percentage of the lubricant depletion and the lower the laser heating temperature, the higher the percentage is. Furthermore, media cooling time plays a significant role in lubricant depletion for the media without a heat sink layer and on glass substrate.

I. Introduction

Heat assisted magnetic recording (HAMR) is a promising choice to overcome the superparamagnetic limit in magnetic recording and further increase the areal recording density of hard disk drive. It uses recording media of very high coercivity, which is too high to be writable for conventional write head. Therefore, a tiny area of the media has to be heated up to a high temperature (>400 ° C) with laser to lower the coercivity temporarily before information can be written on the area. However, HAMR brings about serious problems to slider-disk interface, such as lubricant depletion on disk surface under the high temperature in the heating assisted writing process. Conventional perfluoropolyether (PFPE) lubricants such as Z-Dol 4000 or Z-Tetraol, which are used to coat current magnetic recording media surfaces, cannot withstand the HAMR recording temperatures. Lubricant desorption and/or degradation under laser irradiation was instantaneous and catastrophic, leading to head-disk interface failure [1].