Evolution of Transferred Lubricant Distributions on the Slider Surface Under Ambient and Laser-Heating Conditions

The dynamic equilibrium among the condensation, evaporation and shear flow of the lubricant on a slider has been modeled by solving a continuum-based partial differential equation, with temperatures obtained from a finite element model. Zero-flux and specified-flux boundary conditions were used to study the trailing pad of a slider. The results show that the average lubricant thickness on the trailing pad gradually approaches a steady state, and the steady-state value increases with increasing disk lubricant thickness. A reduction of the flying height leads to a reduced steady-state slider lubricant thickness. The temperature rise of the disk surface tends to promote the lubricant transfer to the slider in a region close to the trailing edge. However, this effect may be locally suppressed by the laser-induced local thinning of the lubricant film on the disk.

Independence between friction and velocity distribution in fluids subjected to severe shearing and confinement

Lubricated friction at high shear and high enough pressure becomes saturated, independently of the velocity profile in the lubricant thickness.

Molecular Dynamics Simulation of Lubricant Transfer Between Slider and Bit Patterned Disk

A modified coarse-grained, bead-spring model for lubricant transfer from a bit patterned media (BPM) disk to a slider is developed using molecular dynamics (MD). The lubricant transfer at slider/BPM disk interface is compared with that at slider/conventional disk interface. In addition, the effect of lubricant thickness and slider flying height is investigated.

Lubricant Evaporation and Flow due to Laser Heating With a Skewed Temperature Distribution Induced by Disk Motion

Due to the fast disk rotation, the temperature distribution on the disk under laser illumination in heat-assisted magnetic recording (HAMR) tends to deviate significantly from an axisymmetric distribution. A lognormal approximation scheme for the temperature distribution containing a tail based on a fast-moving heat source solution was proposed for use in an equation for the lubricant film involving evaporation, surface tension, disjoining pressure and thin-film enhanced effective viscosity. The results reveal the process of formation of a lubricant trough: an indent of the lubricant profile first forms and grows to a steady-state depth, followed by a continuous extension at the rate of the disk velocity. Both evaporation and thermal capillarity due to the surface tension gradient contribute greatly to the creation of a trough in the lubricant profile while the latter also causes boundary ridges. Unlike the Gaussian temperature-based solution, the local minimum of the lubricant thickness occurs at the trailing edge of the thermal spot.

Correlation of Disk Topography Waves With Nanometer Scale Lubricant Moguls

Magnetic recording disk carbon overcoats are lubricated with nanometer thick films of perfluoropolyether lubricant. It is well-known that lubricant thickness redistribution takes place due to air shear stress oscillation at air bearing resonant frequencies and also due to shear stress oscillation induced by disk topography waves on test tracks. We extended this work to demonstrate correlation between surface topography and lubricant redistribution on whole disk surfaces. Lubricant moguls are shown to form over regions of the disk surface which have topography waves that are half the slider length, and the lubricant thickness peak is out of phase down track from the topography peak height. There is a critical relative humidity above 20% beyond which moguls are readily formed by the slider flying at 10 nm without thermal fly height control. The significance of the lubricant redistribution for drive magnetic performance has long been the subject of debate. These results demonstrate that lubricant thickness redistribution on the order of atomic diameters can degrade magnetic performance, and that the surface topography waves alone can degrade areal density by as much as 2%.

A Method to Measure the Media Lubricant Loss After HAMR Recording

Heat assisted magnetic recording (HAMR) is anticipated to increase the areal density in hard disk drives to multiple Tb/in2. During HAMR recording, as a near filed laser light heats the media to the temperature above Curie point to assist magnetic switching, the lubricant that is typically applied to the disk surface will be under an intensive thermal stress, which will lead to the lubricant desorption and/or decomposition, and frequently accompanied with the underneath carbon overcoat (COC) graphitization and oxidation. Due to the optical properties change of the COC at such a high temperature, the traditional optical techniques are not appropriate to measure the lubricant thickness post HAMR recording. In this paper, we introduce a new method based on atomic force microscopy (AFM) in different imaging modes to detect the lubricant and also COC thickness change as a result of laser heating with a vertical resolution at the angstrom scale. Using AFM in a soft tapping mode, we can also characterize the lubricant thickness variation with time after laser exposure, which enables the measurement of the lubricant reflow kinetics on HAMR media.