Marangoni Mechanism in Pulsed Laser Texturing of Magnetic Disk Substrates

This paper proposes a mechanism for topographical features formed during 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 irradiated spot, providing a low contact area bearing for the slider-head of a computer hard drive. Formation of topography is believed to involve gradient capillary forces acting at the surface of the molten pool (Marangoni effect). However, the central peak cannot be explained with thermo-capillary forces alone. Therefore, it is suggested that a compositional gradient due to the depletion of a surfactant at the molten surface provides the necessary condition to reverse the capillary force in the central region. This perspective is investigated using finite element modeling of the Lagrangian fluid mechanics coupled with heat and mass diffusion.