A Direct Simulation Monte Carlo Study of the Environmental Conditions in Nanoscale Air Bearings Affecting Head Smear Formation

We use the direct simulation Monte Carlo (DSMC) method along with the consistent Boltzmann algorithm (CBA) to study the environmental factors affecting smear formation in a representative heat-assisted magnetic recording (HAMR) air bearing. We focus on the humidity, temperature, density, and velocity fields due to the high-temperature hotspot on the head-disk interface. We find that the gas temperature gradient in the vertical direction is significantly smaller than that expected by the temperature difference between the head and disk surfaces. This is possible since the head-disk clearance limits the mean free path of the gas bearing. Consequently, the velocity field of the gas in the vertical direction also showed a drift from the colder to the hotter surface at low spacing. We also observed a high partial pressure of water vapor in the gas bearing, several times higher than the ambient level due to the higher gas temperature and pressure.