EFFECT OF INTERMOLECULAR FORCES ON THE DYNAMIC RESPONSE OF A SLIDER Saurabh K. Deoras Center for Magnetic Recording Research Department of Mechanical and Aerospace Engineering University of California, San Diego San Diego, California 92093-0401 Email: sdeoras@talkelab.ucsd.edu Frank E. Talke Center for Magnetic Recording Research Department of Mechanical and Aerospace Engineering University of California, San Diego San Diego, California 92093-0401 Email: ftalke@ucsd.edu Introduction As the spacing between the slider and the disk approaches atomic distances, near range intermolecular forces start to act at the slider-disk interface. Wu and Bogy have numerically pre- dicted that intermolecular forces become of importance when the slider-disk spacing is lower than 5nm [1]. Thornton and Bogy have proposed that it may not be possible for a slider to fly at a very low flying height without ”snapping” and without hav- ing slider disk contacts [2; 3]. According to their calculations, a slider would ”snap” (get pulled very close) to the disk surface, as a result of attractive intermolecular forces, when the flying height is lowered below a certain ”critical” flying height. How- ever, the question arises whether a slider is likely to ”snap” at flying heights greater than the ”critical” flying height due to its dynamic response. Static Flying Height and the ”Snapping” Effect The slider body is modeled as a point mass. The pitch-II (vertical motion) air-bearing stiffness is modeled as a spring- mass-damper system. The equation for the non-linear change in the air-bearing stiffness was assumed by Thornton et al. to be of the form [3] ks β s α (1) Address all correspondence to this author. 0.5 1 1.5 2 0 0.5 1 1.5 2 Nominal FH [nm] Equilibrium FH [nm] Effect of intermolecular forces on static FH Equilibrium flying height 45 degree line Reduction in the equilibrium flying height due to intermolecular forces "Snapping" (With Intermolecular Forces) (Without Intermolecular Forces) Figure 1. Onset of ”snapping” effect: Bifurcation diagram Figure 1 is a reproduction of the results from Thornton and Bogy, also called ”bifurcation diagram”. We observe that the slider ”snaps” to the surface of the disk at nominal flying heights below 12nm. 1 Copyright  2005 by ASME Proceedings of WTC2005 World Tribology Congress III September 12-16, 2005, Washington, D.C., USA WTC2005-63679