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Effects of a Keeper on Thin Film Magnetic Bits

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2 Author(s)

When Permalloy films are used for computer storage, a magnetic keeper can improve performance by reducing the following undesirable conditions: stray fields from adjacent lines and from adjacent bits; the effect of current spreading in the ground plane; and trapped flux in the ground plane which opposes switching in the absence of a low reluctance path outside the bit. Theoretical analysis and experimental verification of these important keeper functions are presented in this paper. Through the use of high-frequency pulse techniques, effects of both metallic and non-metallic keepers, at distances from the ground plane ranging from 5 to 30 mils, have been determined. By defining efficiency as the percentage reduction in the average of four worst-case effects, the efficiency factor of a metallic keeper is shown to be 56 and that of a non-metallic keeper, 73. It is suggested that better efficiency is due more to lower electrical conductivity than to any intrinsic magnetic properties.

Note: The Institute of Electrical and Electronics Engineers, Incorporated is distributing this Article with permission of the International Business Machines Corporation (IBM) who is the exclusive owner. The recipient of this Article may not assign, sublicense, lease, rent or otherwise transfer, reproduce, prepare derivative works, publicly display or perform, or distribute the Article.  

Published in:

IBM Journal of Research and Development  (Volume:10 ,  Issue: 2 )