Stock material or miscellaneous articles – All metal or with adjacent metals – Having magnetic properties – or preformed fiber orientation...
Reexamination Certificate
2002-02-21
2004-12-07
Bernatz, Kevin M. (Department: 1773)
Stock material or miscellaneous articles
All metal or with adjacent metals
Having magnetic properties, or preformed fiber orientation...
C428S637000, C428S671000, C428S675000, C428S678000, C428S686000, C428S216000, C428S336000, C428S690000, C428S690000
Reexamination Certificate
active
06828036
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to very high areal density magnetic recording media, such as hard disks, which exhibit improved thermal stability, overwrite (OW) capability, and equalized signal-to-media noise ratio (SMNR), and to a method of manufacturing same. More particularly, the present invention relates to a simplified layer structure providing improved longitudinal magnetic recording media utilizing anti-ferromagnetic coupling (AFC) of vertically spaced-apart ferromagnetic layers.
BACKGROUND OF THE INVENTION
Magnetic recording (“MR”) media and devices incorporating same are widely employed in various applications, particularly in the computer industry for data/information storage and retrieval applications, typically in disk form. Conventional thin-film type magnetic media, wherein a fine-grained polycrystalline magnetic alloy layer serves as the active recording layer, are generally classified as “longitudinal” or “perpendicular”, depending upon the orientation of the magnetic domains of the grains of magnetic material.
A portion of a conventional longitudinal recording, thin-film, hard disk-type magnetic recording medium
1
of single magnetic layer constitution, such as commonly employed in computer-related applications, is schematically illustrated in
FIG. 1
in simplified cross-sectional view, and comprises a substantially rigid, non-magnetic metal substrate
10
, typically of aluminum (Al) or an aluminum-based alloy, such as an aluminum-magnesium (Al—Mg) alloy, having sequentially deposited or otherwise formed on a surface
10
A thereof a plating layer
11
, such as of amorphous nickel-phosphorus (Ni—P); a seed layer
12
A of an amorphous or fine-grained material, e.g., a nickel-aluminum (Ni—Al) or chromium-titanium (Cr—Ti) alloy; a polycrystalline underlayer
12
B, typically of Cr or a Cr-based alloy; a magnetic recording layer
13
, e.g., of a cobalt (Co)-based alloy with one or more of platinum (Pt), Cr, boron (B), etc.; a protective overcoat layer
14
, typically containing carbon (C), e.g., diamond-like carbon (“DLC”); and a lubricant topcoat layer
15
, e.g., of a perfluoropolyether. Each of layers
11
-
14
may be deposited by suitable physical vapor deposition (“PVD”) techniques, such as sputtering, and layer
15
is typically deposited by dipping or spraying.
In operation of medium
1
, the magnetic layer
13
is locally magnetized by a write transducer, or write “head”, to record and thereby store data/information therein. The write transducer or head creates a highly concentrated magnetic field which alternates direction based on the bits of information to be stored. When the local magnetic field produced by the write transducer is greater than the coercivity of the material of the recording medium layer
13
, the grains of the polycrystalline material at that location are magnetized. The grains retain their magnetization after the magnetic field applied thereto by the write transducer is removed. The direction of the magnetization matches the direction of the applied magnetic field. The magnetization of the recording medium layer
13
can subsequently produce an electrical response in a read transducer, or read “head”, allowing the stored information to be read.
Adverting to
FIG. 2
, a recent approach for improving the microstructure, texture, and crystallographic orientation of magnetic alloys in the fabrication of thin film, high recording density, longitudinal magnetic recording media
1
′, involves modification of layer system
12
for microstructure control to include a third or “interlayer”
12
C between underlayer
12
B and magnetic recording layer
13
. A number of Co-based alloy materials, such as CoCr, magnetic CoPtCr, CoPtCrTa, CoCrB, CoCrTa, and CoCrTaO
x
(where O
x
indicates surface-oxidized CoCrTa), etc., have been studied for use as intermediate layers
12
C according to such approach, as disclosed in, for example, U.S. Pat. Nos. 5,736,262; 5,922,442; 6,001,447; 6,010,795; 6,143,388; 6,150,016; 6,221,481 B1; and 6,242,086 B1, the entire disclosures of which are incorporated herein by reference.
Magnetic media such as illustrated in
FIG. 2
are advantageously fabricated with simultaneous crystallographic orientation and grain size refinement, by interposition of a “double underlayer” structure (equivalent to a structure represented as
12
B
1
/
12
B
2
, wherein
12
B
1
and
12
B
2
respectively indicate first-deposited and second-deposited underlayers) between the substrate and the magnetic recording layer, e.g., a Cr/Cr
100−x
V
x
or Cr/Cr
100−x
W
x
double underlayer structure, with the Cr first underlayer (=
12
B
1
) being deposited on the seed layer
12
A.
One particular Co-based material suggested for use as interlayer
12
C is CO
63−x
Cr
37
Pt
x
, where x≦8, and a typical layer system
12
including such interlayer may be comprised of a seed layer
12
A, e.g., of amorphous or fine-grained Ni—Al or Cr—Ti, an underlayer
12
B, e.g., of a Cr/Cr
100−x
W
x
double underlayer structure
12
B
1
/
12
B
2
, such as Cr/Cr
90
W
10
, and an interlayer
12
C, e.g., of CO
63−x
Cr
37
Pt
x
, where x≦8.
While the above-described seed layer/underlayer/interlayer structures provide improvement in media performance, further efforts are continually being made with the aim of increasing the areal recording density, i.e., the bit density, or bits/unit area, thermal stability, signal-to-medium noise ratio (“SMNR”), and other properties/characteristics of high areal density magnetic media. However, severe difficulties are encountered when the bit density of longitudinal media is increased above about 20-50 Gb/in
2
in order to form ultra-high recording density media, such as thermal instability, when the necessary reduction in grain size exceeds the superparamagnetic limit. Such thermal instability can, inter alia, cause undesirable decay of the output signal of hard disk drives, and in extreme instances, result in total data loss and collapse of the magnetic bits.
One proposed solution to the problem of thermal instability arising from the very small grain sizes associated with ultra-high recording density magnetic recording media, including that presented by the superparamagnetic limit, is to increase the crystalline anisotropy, thus the squareness of the magnetic bits, in order to compensate for the smaller grain sizes. However, this approach is limited by the field provided by the writing head.
Another proposed solution to the problem of thermal instability of very fine-grained magnetic recording media is to provide stabilization via coupling of the ferromagnetic recording layer with another ferromagnetic layer or an anti-ferromagnetic layer. In this regard, it has been recently proposed (E. N. Abarra et al., IEEE Conference on Magnetics, Toronto, April 2000) to provide a stabilized magnetic recording medium comprised of at least a pair of vertically spaced-apart ferromagnetic layers which are anti-ferromagnetically coupled (“AFC”) by means of an interposed thin, non-magnetic spacer layer. The coupling is presumed to increase the effective volume of each of the magnetic grains, thereby increasing their stability. According to this approach, the coupling strength J between the ferromagnetic layer pairs is a key parameter in determining the increase in stability.
Recently, AFC-type, high areal density longitudinal media have been fabricated utilizing a layer system
12
similar to that described supra with respect to conventionally structured high areal density longitudinal media, i.e., comprised, in sequence, of a seed layer
12
A, a double underlayer structure
12
B
1
/
12
B
2
, and an interlayer
12
C, e.g., an amorphous or fine-grained Ni—Al or Cr—Ti seed layer
12
A, a Cr/Cr
90
W
10
double underlayer structure
12
B
1
/
12
B
2
, and a CO
63
Cr
37
Pt
x
interlayer
12
C, where x≦8. Thus, an AFC-type, high areal density magnetic recording medium including such layer system
12
may be described by the following minimum 7-layer structure: non-magnetic substrate//seed layer
Girt Erol
Munteanu Mariana Rodica
Bernatz Kevin M.
McDermott Will & Emery LLP
Seagate Technology LLC
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