Stock material or miscellaneous articles – Structurally defined web or sheet – Including components having same physical characteristic in...
Reexamination Certificate
2001-11-07
2004-08-17
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including components having same physical characteristic in...
C428S690000, C428S690000, C428S690000
Reexamination Certificate
active
06777066
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to improved perpendicular magnetic recording media with improved signal-to-medium noise ratio (“SMNR”), for use with single-pole transducer heads. The present invention is of particular utility in the manufacture of data/information storage and retrieval media, e.g., hard disks, exhibiting ultra-high areal recording densities of about 200 Gb/in
2
and greater with ultra-low noise characteristics.
BACKGROUND OF THE INVENTION
Magnetic media are widely used in various applications, particularly in the computer industry, and efforts are continually made with the aim of increasing the areal recording density, i.e., bit density of the magnetic media. In this regard, so-called “perpendicular” recording media have been found to be superior to the more conventional “longitudinal” media in achieving very high bit densities. In perpendicular magnetic recording media, residual magnetization is formed in a direction perpendicular to the surface of the magnetic medium, typically a layer of a magnetic material on a suitable substrate. Very high linear recording densities are obtainable by utilizing a “single-pole” magnetic transducer or “head” with such perpendicular magnetic media.
It is well-known that efficient, high bit density recording utilizing a perpendicular magnetic medium requires interposition of a relatively thick (i.e., as compared to the magnetic recording layer), magnetically “soft” underlayer (“SUL”), i.e., a magnetic layer having relatively low coercivity, such as of a NiFe alloy (Permalloy), between the non-magnetic substrate, e.g., of glass, aluminum (Al) or an Al-based alloy, and the “hard” magnetic recording layer, e.g., of a cobalt-based alloy (e.g., a Co—Cr alloy) having perpendicular anisotropy or of a (CoX/Pd or Pt)
n
multi-layer superlattice structure. The magnetically soft underlayer serves to guide magnetic flux emanating from the head through the magnetically hard, perpendicular magnetic recording layer. In addition, the magnetically soft underlayer reduces susceptibility of the medium to thermally-activated magnetization reversal by reducing the demagnetizing fields which lower the energy barrier that maintains the current state of magnetization.
A typical perpendicular recording system
10
utilizing a vertically oriented magnetic medium
1
with a relatively thick soft magnetic underlayer, a relatively thin hard magnetic recording layer, and a single-pole head, is illustrated in
FIG. 1
, wherein reference numerals
2
,
3
,
4
, and
5
, respectively, indicate the substrate, soft magnetic underlayer, at least one non-magnetic interlayer, and vertically oriented, hard magnetic recording layer of perpendicular magnetic medium
1
, and reference numerals
7
and
8
, respectively, indicate the single and auxiliary poles of single-pole magnetic transducer head
6
. Relatively thin interlayer
4
(also referred to as an “intermediate” layer), comprised of one or more layers of non-magnetic materials, is provided in a thickness sufficient to prevent (i.e., de-couple) magnetic interaction between the soft underlayer
3
and the hard recording layer
5
but should be as thin as possible in order to minimize the spacing (HSS in the figure) between the lower edge of the transducer head
6
and the upper edge of the magnetically soft underlayer
3
. In addition, interlayer
4
serves to promote desired microstructural and magnetic properties of the hard recording layer
5
. As shown by the arrows in the figure indicating the path of the magnetic flux &phgr;, flux &phgr; is seen as emanating from single pole
7
of single-pole magnetic transducer head
6
, entering and passing through vertically oriented, hard magnetic recording layer
5
in the region above single pole
7
, entering and travelling along soft magnetic underlayer
3
for a distance, and then exiting therefrom and passing through vertically oriented, hard magnetic recording layer
5
in the region above auxiliary pole
8
of single-pole magnetic transducer head
6
. The direction of movement of perpendicular magnetic medium
1
past transducer head
6
is indicated in the figure by the arrow above medium
1
.
With continued reference to
FIG. 1
, vertical lines
9
indicate grain boundaries of each polycrystalline (i.e., granular) layer of the layer stack constituting medium
1
. As apparent from the figure, the width of the grains (as measured in a horizontal direction) of each of the polycrystalline layers constituting the layer stack of the medium is substantially the same, i.e., each overlying layer replicates the grain width of the underlying layer. Not shown in the figure, for illustrative simplicity, are a protective overcoat layer, such as of a diamond-like carbon (DLC) layer formed over hard magnetic layer
5
, and a lubricant topcoat layer, such as a layer of a perfluoropolyethylene material, formed over the protective overcoat layer. Substrate
2
is typically disk-shaped and comprised of a non-magnetic metal or alloy, e.g., Al or an Al-based alloy, such as Al—Mg having an Ni—P plating layer on the deposition surface thereof, or substrate
2
is comprised of a suitable glass, ceramic, glass-ceramic, polymeric material, or a composite or laminate of these materials; soft magnetic underlayer
3
is typically comprised of an about 2,000 to about 4,000 Å thick layer (or a pair of layers) of a soft magnetic material selected from the group consisting of Ni, NiFe (Permalloy), Co, CoZr, CoZrCr, CoZrNb, CoFe, Fe, FeN, FeSiAl, FeSiAlN, etc.; interlayer
4
typically comprises an up to about 10 Å thick layer (or layers) of at least one non-magnetic material, such as Pt, Pd, Ir, Re, Ru, Hf, alloys thereof, TiCr, and Co-based alloys; and hard magnetic layer
5
is typically comprised of an about 100 to about 250 Å thick layer of a Co-based alloy including one or more elements selected from the group consisting of Cr, Fe, Ta, Ni, Mo, Pt, V, Nb, Ge, and B, iron oxides, such as Fe
3
O
4
and &dgr;-Fe
2
O
3
, or a (CoX/Pd or Pt)
n
multilayer magnetic superlattice structure, where n is an integer from about 10 to about 25, each of the alternating, thin layers of Co-based magnetic alloy is from about 2 to about 3.5 Å thick, X is an element selected from the group consisting of Cr, Ta, B, Mo, and Pt, and each of the alternating thin, non-magnetic layers of Pd or Pt is about 10 Å thick. Each type of hard magnetic recording layer material has perpendicular anisotropy arising from magneto-crystalline anisotropy (1
st
type) and/or interfacial anisotropy (2
nd
type).
Another way of classifying perpendicular magnetic recording media into different types is based on the media properties provided by the material utilized for the magnetically hard recording layer. For example, as indicated above, the magnetically hard, perpendicular recording layer can comprise magnetic alloys which are typically employed in longitudinal media, e.g., CoCr alloys, or multilayer magnetic superlattice structures, such as the aforementioned (CoX/Pd or Pt)
n
superlattice structures. Representative M-H hysteresis loops of magnetic recording layers comprised of these different types of materials are shown in FIGS.
2
(A)-
2
(B). As is evident from FIG.
2
(A) showing the M-H loop of a perpendicular recording medium comprising a CoCr alloy, such type media typically exhibit a relatively low coercivity, low remanent squareness, i.e., less than 1, and a positive nucleation field H
n
. In addition, the occurrence of magnetic domain reversal within bits, caused by the presence of high demagnetization fields in CoCr-based perpendicular recording media, is problematic with such media in that the phenomenon is a significant source of media noise reducing the SMNR. A high remanent squareness and a negative nucleation field H
n
are required in order to obtain good bit stability.
By contrast, and as evidenced by FIG.
2
(B) showing the M-H loop of a perpendicular recording medium comprising a (CoX/Pd)
n
multilayer magnetic superlattice structure, such type media adva
Chang Chung-Hee
Ranjan Rajiv Yadav
McDermott Will & Emery LLP
Resan Stevan A.
Seagate Technology LLC
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