Figure - available from: Scientific Reports
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(a) Schematic view of the HAMR Head-Disk Assembly (Not to scale). Two directions are also shown relative to the head. The down-track direction is along the circumferential direction on the disk, and the vertical direction is perpendicular to it. The cross-track direction is along the width of the head and into the plane of the schematic (b) Experimental image of smear on the head after HAMR writing⁵.
Source publication
A main challenge in Heat-Assisted Magnetic Recording technology is the build-up of contaminants called smear on the near field transducer. In this paper, we investigate the role of optical forces originating from the electric field gradient in the formation of smear. First, based on suitable theoretical approximations, we compare this force with ai...
Citations
... The presence of the TFC (Thermal fly-height control) heater and NFT (Near-field transducer) on the head raises the temperature above 700 K with temperature gradients exceeding 10 9 K/m. Further, the NFT forms a local protrusion [6] and induces electric field gradients exceeding 10 16 V/m 2 [7]. The space between the head and the disk forms an air bearing of helium or air. ...
... Since we made no assumption on the size and mass of the helium atom, Eq. 9 can be used for any spherical atom or molecule using an appropriate U(r). Further, in addition to these forces, other effects such as optical forces [7] and ballistic jumps [21] can influence PFPE molecules. However, the conditions where they are significant, such as the presence of metallic nanoparticles or sub 4-nm spacing, are not present in this study. ...
This report investigates the kinetics of lubricant molecules in the HAMR air bearing to understand the initiation and growth of PFPE contamination on the head surface. The collisions with the air bearing induce three forces—drag, thermophoresis, and lift. Of these, we find that lift forces are negligible. Then, a sensitivity analysis of the remaining two forces reveals the conditions where they dominate. Further, a hybrid simulation strategy is utilized to track their movements. The results show that the contaminations (smear) highly depend on the interplay between the thermophoresis and drag forces. We then explain the mechanism of the formation of the various observed patterns. Finally, we offer some recommendations to exploit the air bearing to contain smear on the head.
