MARANGONI MECHANISM IN PULSED-LASER TEXTURING OF MAGNETIC DISK SUBSTRATES

This paper proposes a mechanism for topographical features formed duri ng pulsed laser texturing of Ni-P magnetic disk substrates. A salient feature of the process is the ability to raise a central peak in the i rradiated spot, providing a low contact area bearing for the slider-he ad of a computer hard drive. Formation of topography is believed to in volve gradient capillary forces acting at the surface of the molten po ol (Marangoni effect). However, the central peak cannot be explained w ith thermo-capillary forces alone. Therefore, it is suggested that a c ompositional gradient due to the depletion of a surfactant at the molt en surface provides the necessary condition to reverse the capillary f orce in the central region. This perspective is investigated using fin ite element modeling of the Lagrangian fluid mechanics coupled with he at and mass diffusion.