Laser-induced local heating and lubricant depletion in heat assisted magnetic recording systems

The present study concerns the depletion of thin lubricant film on a disk surface subject to repeated heating by a scanning laser in a heat assisted magnetic recording (HAMR) system. The absorption rate of optical energy by the disk medium is derived from Maxwell equations, which is incorporated into the energy equation by a source term. Both the temperature and the temperature gradient have important effects on lubricant thickness, which, in turn, influences lubricant dynamics and evaporation via the disjoining pressure. The heat loss via convection from the disk surface becomes significant only when the convective heat transfer coefficient is bigger than 109 W/(K m2). With an increase in the absorption coefficient β, the maximum temperature on the disk increases while the heat penetrating depth decreases. For the same energy absorptivity, the surface temperature and, in consequence, lubricant depletion, predicted by the present optical absorption model is lower than that obtained by simplifying the laser heating as a heat flux at the disk surface. By adjusting empirical absorptivity, the heat flux model can produce the same heat transfer results and, in consequence, the same lubricant depletion results, as those predicted by the optical absorption model only when β ⩾ 108 m−1.