Dynamic Adhesion Characteristics of Spherical Sliders Colliding with Stationary Magnetic Disks with a Thin Lubricant Layer

The dynamic indentation characteristics of 1- and 2-mm-radius hemispherical glass sliders when colliding with stationary magnetic disks under various lubricant conditions were investigated to clarify the dynamic interfacial forces between flying head sliders and magnetic disks. The collision times were ~15 and ~30 μs, respectively, and independent of the impact velocity. For a 1-mm-radius slider (Ra roughness = 1.71 nm), a clear adhesion force nearly equal to the static pull-off force was observed at the instant of separation when the lubricant thickness was from 1 nm without UV (0.69 nm mobile lubricant thickness) to 3 nm with UV (1.89 nm mobile lubricant thickness). The dynamic adhesion force was maximum when the slider had separated from the disk surface by about 2 nm and dropped from the maximum to zero when the separation reached more than 5 nm. When the mobile lubricant thickness was 0.43 nm, a clear adhesion force was not observed. For a 2-mm-radius slider (Ra roughness = 0.34 nm), a clear adhesion force, similar to the static pull-off force, was observed at the instant of separation at almost all lubricant thicknesses and impact velocities tested except at a small mobile lubricant thickness of 0.43 nm with impact velocities greater than 1.1 mm/s. The dynamic adhesion force dropped from the maximum to zero when the distance traveled from the maximum reached more than 5 nm. These results suggest that the dynamic adhesion force of 1- and 2-mm-radius sliders originates from meniscus formation rather than van der Waals force.