Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-07-25
2003-12-23
Rickman, Holly (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S690000, C428S900000, C428S216000, C428S336000, C204S192100, C204S192200, C427S129000, C427S131000, C427S132000
Reexamination Certificate
active
06667118
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an improved method for forming soft magnetic underlayers for magnetic recording media having uniaxial anisotropy and to improved magnetic recording media including such uniaxially anisotropic soft magnetic underlayers. The present invention is of particular utility in the manufacture of high areal recording density perpendicular magnetic recording media, e.g., hard disks, which exhibit substantially reduced Barkhausen noise.
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 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, 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. The magnetically soft underlayer serves to guide magnetic flux emanating from the head through the 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, serves to (1) prevent magnetic interaction between the soft underlayer
3
and the hard recording layer
4
and (2) promote desired microstructural and magnetic properties of the hard recording layer. 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) formed over hard magnetic layer
5
, and a lubricant topcoat layer, such as 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 NiP 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; underlayer
3
is typically comprised of an about 2,000 to about 4,000 Å thick layer of a soft magnetic material selected from the group consisting of Ni, NiFe (Permalloy), Co, CoZr, CoZrCr, CoZrNb, CoFe, Fe, FeN, FeSiAl, FeSiAlN, etc.; 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 1 Å thick. Each type of hard magnetic recording layer material has perpendicular anisotropy arising from magneto-crystalline anisotropy (1
st
type) and interfacial anisotropy (2
nd
type).
A significant problem and drawback associated with the utilization of soft magnetic underlayers, such as layer
3
shown in
FIG. 1
, is the generation of noise resulting from, inter alia, pinning and unpinning (i.e., motion) of the magnetic domain walls thereof, termed “Barkhausen noise”, which noise adversely affects performance characteristics of magnetic media, particularly high bit density magnetic media.
Accordingly, there exists a need for an improved method for manufacturing high bit density perpendicular magnetic information/data recording, storage, and retrieval media including magnetically soft underlayers, but which exhibit no, or at least substantially reduced, Barkhausen noise. In addition, there exists a need for improved, high bit density perpendicular magnetic recording media employing magnetically soft underlayers which exhibit no, or at least substantially reduced, Barkhausen noise, which media can be readily and economically fabricated by means of conventional manufacturing techniques and instrumentalities.
The present invention addresses and solves problems attendant upon the use of magnetically soft underlayers in the manufacture of high bit density perpendicular magnetic media, e.g., generation of Barkhausen noise, while maintaining all structural and mechanical aspects of high bit density recording technology. Moreover, the magnetic media of the present invention can be fabricated by means of conventional manufacturing techniques, e.g., sputtering.
DISCLOSURE OF THE INVENTION
An advantage of the present invention is an improved method of manufacturing a magnetic recording medium having no, or at least substantially reduced, Barkhausen noise.
Another advantage of the present invention is an improved method of manufacturing a high areal density, perpendicular magnetic recording medium wherein Barkhausen noise is at least substantially suppressed.
Still another advantage of the present invention is an improved magnetic recording medium with no, or at least substantially reduced, Barkhausen noise.
Yet another advantage of th
Chang Chung-Hee
Ranjan Rajiv Yadav
McDermott & Will & Emery
Rickman Holly
Seagate Technology LLC
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