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Magnetic Disk for High Density Recording

IP.com Disclosure Number: IPCOM000104716D
Original Publication Date: 1993-May-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 2 page(s) / 91K

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Gambino, RJ: AUTHOR [+2]


Disclosed is a method of controlling crystal structure of magnetic material used for high density magnetic recording material.

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Magnetic Disk for High Density Recording

      Disclosed is a method of controlling crystal structure of
magnetic material used for high density magnetic recording material.

      High coercivity materials must be used for high density
recording, where the medium consists of single magnetic domain
particles formed of crystalites with size of order 100 angstrom If
the size, shape, and orientation of the polycrystals of the magnetic
material could be controlled, the material would have higher magnetic
anisotropy and narrower magnetic transitions so that they could be
used for higher density recording.

      It is well known from laser annealing studies of silicon and
other crystalline materials that polycrystals propagate from the edge
of the molten material into the melt, and the resulting material has
gain boundaries substantially perpendicular to the melt boundary.
The proposal is to write tracks on a metallic layer which will be
used as the substrate when laying down the magnetic layer.  The
underlying crystal structure of the substrate will then control the
crystal structure of the magnetic material.

      Fig. 1 sketches the set up to "write" the tracks.  A
multiplicity of laser beams 1 is focussed on the surface 2 of the
disk 3.  The disk 3 is spun at high speed, say, 6000 rpm, and the
laser beam focussing lenses 4 follow the surface 2 of the disk with
techniques well known in the art.  An argon ion laser beam can be
focussed to a spot size of 1 micron at the surface with a 5 micron
depth of focus, which is much easier that the typical inexpensive CD
player technology.  The laser beams are moved out on a radius at a
rate of 1 micron/revolution, so a series of overlapping tracks is
written in the metal.  The material, especially if it is a 2 phase
material, will break into a series of polycrystal grains which are
long and thin and oriented perpendicular to the track.  The laser
will write a 1 micron wide track at the rate of 100 microns per
microsec, which is about the time needed for recrystallization.  At
this rate, the laser beam should be about 1 watt.  A single 20 watt
argon ion laser could be broken up into 10 beams to write a 30 cm
disk in 1 minute.

      A magnetic m...