This thesis investigates the mechanisms that lead to pole tip recession (PTR) in laminated magnetic recording heads (also known as "sandwich heads"). These heads provide a platform for the utilisation of advanced soft magnetic thin films in practical recording heads suitable for high frequency helical scan tape recording systems. PTR results from a differential wear of the magnetic pole piece from the tape-bearing surface of the head. It results in a spacing loss of the playback or read signal of 54.6dB per recording wavelength separation of the poles from the tape. PTR depends on the material combination used in the
head, on the tape type and the climate - temperature and relative humidity (r.h.). Five head materials were studied: two non-magnetic substrate materials- sintered multi granular
CaTi0
3 and composite CaTi0
3/ZrTi0
4/Ti0
2 and three soft magnetic materials- amorphous
CoNbZr, and nanocrystalline FeNbSiN and FeTaN. Single material dummy heads were
constructed and their wear rates measured when cycling them in a Hi-8 camcorder against
commercially available metal particulate (MP) and metal evaporated (ME) tapes in three
different climates: 25°C/20%r.h., 25°C/80%r.h. and 40°C/80%r.h. X-ray photoelectron
spectroscopy (XPS) was used to examine changes the head surface chemistry. Atomic
force microscopy (AFM) was used to examine changes in head and tape surface
topography. PTR versus cycling time of laminated heads of CaTi0
3/ZrTiO
4/Ti0
2 and
FeTaN construction was measured using AFM. The principal wear mechanism observed
for all head materials was microabrasion caused by the mating body - the tape surface. The
variation in wear rate with climate and tape type was due to a variation in severity in this
mechanism, except for tape cycling at 40°C in which gross damage was observed to be
occurring to the head surface. Two subsidiary wear mechanisms were found: third body
scratching (all materials) and grain pullout (both ceramics and FeNbSiN). No chemical
wear was observed, though tribochemical reactions were observed on the metal head
surfaces. PTR was found to be caused by two mechanisms - the first differential
microabrasion of the metal and substrate materials and which was characterised by a low
(~10nm) equilibrium value. The second was by deep ploughing by third body debris
particles, thought mainly to be grain pullout particles. This level of PTR caused by this
mechanism was often more severe, and of a non-equilibrium nature. It was observed more
for ME tape, especially at 40°C/80%r.h. and 25°c/20%r.h. Two other phenomena on the
laminated head pole piece were observed and commented upon: staining and ripple
texturing.
Date of Award | Jun 1999 |
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Original language | English |
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Awarding Institution | |
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Supervisor | John L Sullivan (Supervisor) |
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- tribology
- laminated magnetic recording heads
The tribology of laminated magnetic recording heads
Harrison, M. J. K. (Author). Jun 1999
Student thesis: Doctoral Thesis › Doctor of Philosophy