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

Abstract

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 ls, 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.

Numerical Analysis of Contact Mechanics between a Spherical Slider and a Flat Disk with Low Roughness Considering Lennard–Jones Surface Forces

“…These parameter values are the same as those of the 2-mm-radius glass slider and magnetic disk used for the dynamic adhesion force measurements [19,20]. Accurate values of the Hamaker constant and the atomic equilibrium distance are not known.…”

“…Ono and Nakagawa [19,20] measured the dynamic adhesion force that was applied on the slider when 1-and 2-mm-radius glass sliders collided with a magnetic disk with a molecularly thin lubricant layer. They concluded that the adhesion force observed at the instant of separation after a short contact period of 15-30 µs was caused by the meniscus force rather than by vdW force.…”

Dynamic instability of flying head slider and stabilizing design for near-contact magnetic recording

“…Considering the experimental results of Li et al [12], we established a theory of interfacial force caused by meniscus formation in the toe-dipping regime and performed dynamic analysis on a flying head slider using a simple two-degree-offreedom (2-DOF) model [3,6,[16][17][18]. We also experimentally investigated the dynamic adhesion force that occurs when a spherical slider collides with a magnetic disk [19,20]. Fig.…”

“…The roughness of the disk was 0.52 nm, force calculated from 4pRg (R: mean asperity radius, g: lubricant surface tension ¼ 22 mN/m). The adhesion force dropped to zero when the slider travelled more than 5 nm from the initial disk surface height (details are given elsewhere [19,20]). These findings indicate that a meniscus in the flooded regime can form in a short period (15 ms) even when the surface of the glass slider is rough and that the dynamic adhesion force originates from meniscus force rather than van der Waals force.…”

“…Velocity change of spherical glass slider with 1-mm-radius bouncing on lubricated disks with lubricant thickness of $1 or $2 nm with and without ultraviolet (UV) irradiation (T t : total lubricant thickness, T m : mobile lubricant thickness)[20]: (a) T t ¼ 1.08 nm, w/UV, T m ¼ 0.43 nm; (…”