Research Papers: Magnetic Storage

Stress Induced Permanent Magnetic Signal Degradation of Perpendicular Magnetic Recording System

[+] Author and Article Information
Sung-Chang Lee1

 Samsung Information Systems America, 75 W. Plumeria Drive, San Jose, CA 95134sungc.lee@samsung.com

Soo-Youl Hong, Na-Young Kim, Joerg Ferber, Xiadong Che

 Samsung Information Systems America, 75 W. Plumeria Drive, San Jose, CA 95134

Brian D. Strom

 Apple Inc., 1 Infinite Loop, MS5-Q Cupertino, CA 95014


Corresponding author.

J. Tribol 131(1), 011904 (Dec 03, 2008) (6 pages) doi:10.1115/1.2991123 History: Received March 05, 2008; Revised August 05, 2008; Published December 03, 2008

Model scratches of the size found in hard disk drives are produced under controlled conditions at a series of applied loads on both longitudinal magnetic recording (LMR) media and perpendicular magnetic recording (PMR) media using a diamond tip. The scratches are created at low speed, eliminating thermal considerations from the interpretation of the media response. Nanoindentations are produced as well. The scratches and indentations are characterized by atomic force microscope (AFM), magnetic force microscope (MFM), and also by the same magnetic reader and writer used in an integrated hard disk drive (HDD). A comparison of the response of PMR and LMR media shows the PMR media to have larger scratches and greater magnetic signal degradation than LMR media for a given scratch load. The extent of magnetic damage, as measured by MFM, is greater than the extent of surface mechanical damage, as measured by AFM. Analysis of scratches using the HDD reveals that the magnetic damage is irreversible and permanent damage in magnetic layer, which is confirmed by cross section transmission electron microscope image. The experiments reveal the mechanism for magnetic scratch erasure in the absence of thermal effects. This understanding is expected to lead to improved designs for mechanical scratch robustness of next-generation PMR media.

Copyright © 2009 by American Society of Mechanical Engineers
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Figure 1

Layers of LMR and PMR disk samples used in this study

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Figure 2

Hysitron TriboIndenter system for nanoindentation and nanoscratch on disk and HDD samples. Radius of nanoindentation tip (Berkovich tip) used in this study was 100–200 nm.

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Figure 3

Cross section average along nanoscratch direction of MFM images: (a) LMR media sample with 100 μN load; (b) PMR media sample with 100 μN load

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Figure 4

Comparison of mechanical scratch and magnetic signal erasure using cross section average along nanoscratch line: (a) LMR media with 60 μN load; (b) PMR media with 60 μN load. Width of magnetic signal erasure is slightly larger than width of mechanical scratch in both cases.

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Figure 5

(a) Penetration depth during nanoscratch versus residual depth after nanoscratch with PMR media. Magnetic signal degradation was first observed when penetration depth was about 4 nm with normal load of 20 μN; (b) Comparison between LMR residual depth and PMR residual depth after nanoscratch tests.

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Figure 6

(a) and (b) AFM and MFM images after nanoindentation of 500 μN load with PMR media; (c) cross section image along nanoindentation and written pattern

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Figure 7

Read-back (magnetic) signal degradation of PMR HDD after nanoscratch tests: (a) 100 μN, (b) 50 μN, and (c) 20 μN. Note that (c) shows the running average of the amplitude because the scratch is hard to distinguish otherwise in this light load case of 20 μN. Good agreement between PMR disk and PMR HDD data was found. The same Berkovich tip was used for both PMR HDD and PMR disk samples. The scratch width was evaluated manually and has to be corrected with the skew angle between track and nanoscratch.

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Figure 8

Cross section TEM image of nanoscratched PMR media (50 μN load)



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