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Method for Distinguishing Between Slider-Induced Erasure And Relaxation of Written Transitions

IP.com Disclosure Number: IPCOM000120580D
Original Publication Date: 1991-May-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 3 page(s) / 135K

Publishing Venue

IBM

Related People

Eaton, RE: AUTHOR [+4]

Abstract

Disclosed is a method for non-invasive measuring, from prerecorded transitions on a magnetic medium, partial magnetic erasure caused by the slider and temperature or mechanical stress-induced relaxation caused by slider-disk interaction. The method includes means to distinguish between the effect of partial erasure and temperature/stress induced relaxation. The method utilizes the readback signal of the recording head for deriving this information from previously written transitions. It is, therefore, a non-invasive, in-situ measurement that can be performed on completely assembled disk (and tape) drives to check for HDI related problems.

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This is the abbreviated version, containing approximately 51% of the total text.

Method for Distinguishing Between Slider-Induced Erasure And Relaxation
of Written Transitions

      Disclosed is a method for non-invasive measuring, from
prerecorded transitions on a magnetic medium, partial magnetic
erasure caused by the slider and temperature or mechanical
stress-induced relaxation caused by slider-disk interaction.  The
method includes means to distinguish between the effect of partial
erasure and temperature/stress induced relaxation.  The method
utilizes the readback signal of the recording head for deriving this
information from previously written transitions.  It is, therefore, a
non-invasive, in-situ measurement that can be performed on completely
assembled disk (and tape) drives to check for HDI related problems.

      In DASD devices it has been observed that the ceramic
head-slider material may contain undesirable ferromagnetic inclusions
which can cause partial erasure of the track(s) directly underneath
these inclusions noticeable either at nominal velocity, at reduced
velocity or at touch-down. Such partial erasure may also be brought
about by a recording head whose yoke shows non-zero remanence after a
write operation due to an undesirable magnetic domain pattern in the
head yoke.  It has further been observed that, upon contact between
the slider/head and the recording medium, the resulting increased
temperatures caused by friction and/or the resulting mechanical
stresses can produce a demagnetization of transitions in the tracks
underneath the air-bearing rails of the slider.

      The effect of (partial) magnetic erasure on the written
transitions will first be explained.  As shown in Fig. 1, one or more
tracks are written on a DC-erased recording medium.  The associated
remnant magnetization distribution in the magnetic medium is shown in
Fig.  1(b).  The resultant head readback signal is shown in Fig.
1(c).  Now these transitions are assumed to be partially erased by a
magnetic field weak with respect to the nominal head write field.  In
Fig. 1(d) this is shown by way of example for the weak field produced
by the remanent magnetic poletips.  This field will lower the
magnetization of the bit cell in the opposite direction.  This leads
to a lower step in Mr (as shown in Fig. 1(e)) and a smaller
associated transition. The moment the weak erase field has arrived at
the left-hand side of the bit cell that is magnetized in the
direction opposite the erase field, the total field (i.e. the erase
field plus the bias field of the magnetization at the right-hand side
of the bit cell end) becomes strong enough to further erase the
magnetization and more so towards the end of the bit cell.  The
result is a change in the slope of the Mr step inside the bit cell
at the end of the bit cell. The resulting...