Molecularly Structural Change of PFPE Lubricant Accumulated on Pin Surface at Laser Heating

Abstract

With increase in the storage capacity of hard disk drives, the flying height of the magnetic head is now typically less than a few nanometers. Picked up lubricant on the slider surface causes the head flying instability. On the head disk interface (HDI) of heat assisted magnetic recording (HAMR), the disk surface is heated to a high temperature of 400 – 500 K. If the lubricant is evaporated by laser heating and that should accumulate as smear on the slider surface. Kiely et al. concluded that the head smear played a key role not only for the stability of the HDI, but also for the transmission efficiency of the thermal energy from the near field transducer to the recording media in the HAMR system [1]. In this study, we have studied the molecularly structural change of perfluoropolyether (PFPE) lubricant accumulated on the pin surface at laser heating using TOF-SIMS in order to obtain the design guideline of lubricant film with the high heat resistance for the HAMR. TOF-SIMS spectrum of lubricant accumulated on a pin surface was compared to that of disk lubricant inside and outside laser heated track as shown in Fig. 1. The molecular weight could be obtained from these TOF-SIMS spectra. In addition, the progress of end-groups dissociation by laser heating could be estimated by the intensity of end-group fragments. As the results, the molecular weight of accumulated lubricant was smaller than that of disk lubricant and that of disk lubricant was larger than that of normal lubricant. The dissociation of end-groups increased with the temperature of laser heating as shown in Fig. 2.