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Research Papers: Magnetic Storage

Experimental and FEA Scratch of Magnetic Storage Thin-Film Disks to Correlate Magnetic Signal Degradation With Permanent Deformation

[+] Author and Article Information
Raja R. Katta

Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801

Andreas A. Polycarpou1

Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801polycarp@illinois.edu

Sung-Chang Lee, Mike Suk

 Samsung Information Systems America, San Jose, CA 95134

1

Corresponding author.

J. Tribol 132(2), 021902 (Mar 11, 2010) (11 pages) doi:10.1115/1.4000848 History: Received March 07, 2009; Revised December 02, 2009; Published March 11, 2010; Online March 11, 2010

Scratch-related magnetic signal degradation can occur during magnetic storage hard disk drive operations when the read-write heads contact the spinning multilayer disks. To investigate this phenomenon, controlled nanoscratch experiments were performed on perpendicular magnetic recording media using various indenters of different radii of curvature. Various loading conditions were used to cause permanent scratches that were measured using atomic force microscopy. The nanoscratch experiments were simulated using finite element analysis (FEA) that included the detailed nanometer scale thin-film multilayer mechanical properties. The permanently deformed field in the subsurface magnetic recording layer was extracted from the FEA results. The residual scratch widths measured on the surface of the magnetic storage disk were directly compared with the residual subsurface widths of the region on the magnetic recording layer, where extensive permanent lateral deformation was present. It was found that the subsurface widths of the deformed regions were significantly larger than the surface scratch widths. Thus, subsurface thin-film layers, such as the magnetic recording layer, could be damaged without observable damage to the protective top surface carbon overcoat. The exact location and extent of damage to the magnetic recording layer depends on the scratch load, size of scratch tip, and the friction at the interface. Such permanent deformation in magnetic recording layer could lead to demagnetization, which has been reported in the literature.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic of a typical PMR multilayer magnetic disk

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Figure 2

Typical measured AFM image of two nanoscratches with tip A (R=240 nm): (a) overall top view; (b) zoomed-in isometric view, P=80 μN; and (c) cross-sectional view of the scratch in (b)

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Figure 3

FEA mesh used for tip A (R=240 nm) and tip B (633 nm)

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Figure 4

Extracted nanomechanical properties obtained using the corrected OP nanoindentation technique for the top 10 nm of multilayer structure: (a) reduced elastic modulus Er; and (b) hardness H

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Figure 5

FEA stress contours for tip A (R=240 nm), P=50 μN: (a) maximum principal stress; and (b) maximum von Mises stress with DLC layer not shown for better visualization. Units: GPa, + symbols indicate locations of maximum values.

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Figure 6

FEA stress magnitudes in each layer for tip A, P=50 μN: (a) maximum principal stress; and (b) maximum von Mises stress (see Table 1 for each layer’s yield strength value)

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Figure 7

FEA stress contours for tip B (R=633 nm), P=100 μN: (a) maximum principal stress; (b) maximum von Mises stress (DLC layer not shown). Units: GPa, + symbols indicate locations of maximum values.

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Figure 8

FEA stress magnitudes in each layer for tip B, P=100 μN: (a) maximum principal stress; (b) maximum von Mises stress (see Table 1 for each layer’s yield strength value)

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Figure 9

FEA stress contours for tip C (R=5.2 μm), P=9 mN: (a) maximum principal stress; (b) maximum von Mises stress (DLC layer not shown). Units: GPa, + symbols indicate locations of maximum values.

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Figure 10

FEA stress magnitudes in each layer for tip C, P=9 mN: (a) maximum principal stress; (b) maximum von Mises stress (see Table 1 for each layer’s yield strength value)

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Figure 11

Direct residual scratch cross-sectional view comparison between FEA and experiment (Tip A, R=240 nm, P=80 μN)

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Figure 12

Comparison of nanoscratch FEA versus experimental maximum and residual penetration depths: (a) tip A, R=240 nm; (b) tip B, R=633 nm; (c) tip C, R=5.2 μm

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Figure 13

FEA maximum equivalent plastic strain for (a) tip A (R=240 nm), P=50 μN; (b) tip B (R=633 nm), P=100 μN after scratch (DLC layer not shown). + symbols indicate locations of maximum values.

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Figure 14

FEA maximum lateral deformation (X-displacement) contours (DLC layer not shown) for (a) tip A (R=240 nm), P=50 μN; (b) tip B (R=633 nm), P=100 μN after scratch. Units: nm, + symbols indicate locations of maximum values.

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Figure 15

Comparison of experimental surface scratch width versus FEA surface scratch width: (a) R=240 nm; (b) R=633 nm

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Figure 16

FEA comparison of surface scratch width versus subsurface width of the MAG layer deformed region: (a) R=240 nm; (b) R=633 nm

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