Pronounced effect of under layers on the squareness and slope T of the
perpendicular loops of very thin CoCr films was observed. Experimental and theoretical
studies suggest that, depending on the film microstructure, there are two origins on the
anomalous shearing of perpendicular loops of Cc-based perpendicular films: the columnar
shape anisotropy and the wall-motion-like magnetization reversal process. For films with
larger intercolumnar separation, the contribution of the columnar shape anisotropy to the
total demagnetizing factor is mainly responsible for the deshearing of the loops. For continuous
perpendicular films, the intergranular exchange coupling controls the magnetization
reversal process and the wall-motion-like reversal explains the anomalous shearing of the
hysteresis loop. The square and desheared perpendicular loops of very thin CoCr films
originated from their strong perpendicular anisotropy and large intergranular nonmagnetic
separation.
Study of the orientation relationship between the Co-based films and their underlayers
suggested that the texture of the very thin CoCr and CoCrTa films is determined by
the thermodynamic nature of hcp Co crystal itself and the nature of the underlayers or
substrates on which it grows. Amorphous underlayers provide "neutral" substrate surfaces
for. the [0002] self-oriented growth of hcp Co-based films. Hcp Ti and [111] textural fee
Pt, Au underlayers favour the [0002] oriented epitaxial growth. [100] or [110] textural bee
Cr underlayers favour the [1010] oriented growth.
The perpendicular coercivity of a Co-based medium is determined by its crystalline
anisotropy and intergranular exchange coupling, and can be largely affected by the morphology
of its underlayers. The larger perpendicular coercivity of the CoCrTa films on
Ti underlayers was mainly due to the large grain diameter which results in a reduction
in the intergranular exchange coupling constant. The difference between the surface and
bulk coercivity of the CoCrTa films on Ti underlayers was attributed to the improvement
of the crystallographic orientation of the hcp Co crystals and the development of large
grains as the film grows thicker, which causes the reduction in the surface intergranular
exchange coupling due to large grains as well as large intergranular separation.
Co84Nb12Fe4 amorphous films were investigated as back-layers for double layer media.
Very low coercivity down to 0.0125 Oe was achieved for films of 10000 Å-thick with a
saturation magnetic induction of 11 kG. The thickness dependence of coercivity follows
the Neel formula for films thicker than 400 Å.
A D5o density of 160 KFRPI was achieved for the 2000 Å-thick medium on Pt underlayers
using MIG heads of gap length 0.15 µm. Experimental and theoretical analyses of
the read/write processes show both the achieved D5o density and the reproduced output
level for these media were head field and head-medium spacing limited. Lower medium
noise and higher SNR were achieved by the media with Ti underlayers, which supports
the intergranular exchange coupling noise theory.
Date of Award | 1993 |
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Original language | English |
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Awarding Institution | |
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Investigation into the Microstructure, Magnetic Properties and Read/write Performance of Thin-film Media for Perpendicular Recording Computer Disks
Pan, G. (Author). 1993
Student thesis: PhD