Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Reexamination Certificate
2001-07-11
2003-11-11
Rickman, Holly (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
C428S216000, C428S611000, C428S667000, C428S668000, C428S690000, C428S900000, C427S128000, C427S131000
Reexamination Certificate
active
06645614
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to very high areal recording density longitudinal magnetic recording media exhibiting improved thermal stability, such as hard disks. More particularly, the present invention relates to improved magnetic recording media including an interface layer between a spacer layer and a magnetic layer for providing enhanced magnetic coupling, i.e., RKKY-type coupling, between 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 magnetic thin-film media, wherein a fine-grained polycrystalline magnetic alloy layer serves as the active recording medium layer, are generally classified as “longitudinal” or “perpendicular”, depending upon the orientation of the magnetic domains of the grains of magnetic material.
A conventional longitudinal recording, hard disk-type magnetic recording medium
1
commonly employed in computer-related applications is schematically illustrated in
FIG. 1
, and comprises a substantially rigid, non-magnetic metal or glass 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) alloy, a chromium-titanium (Cr—Ti) alloy, a tantalum (Ta) layer, or a tantalum nitride (TaN) layer; 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.
Efforts are continually being made with the aim of increasing the areal recording density, i.e., the bit density, or bits/unit area, and signal-to-medium noise ratio (“SMNR”) of the 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, because the necessary reduction in grain size reduces the magnetic energy, E
m
, of the grains to near the superparamagnetic limit, whereby the grains become thermally unstable. 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, is to increase the crystalline anisotropy and therefore increase the magnetic energy of the grains, 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 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; the coupling strength between the ferromagnetic layer pairs being a key parameter in determining the increase in stability.
However, a significant drawback associated with the above approach is observed when a pair of ferromagnetic layers of alloy compositions which exhibit superior performance when utilized in conventional longitudinal magnetic recording media, e.g., Co—Cr and Co—Cr—Pt alloys, are coupled across an interposed thin, non-magnetic spacer layer. Specifically, the observed coupling is, in general, significantly lower than that observed with layers composed of pure (i.e., unalloyed) Co. For example,
FIG. 2
shows M(H) loops in the first quadrant for graphically illustrating the decrease in anti-ferromagnetic coupling (“AFC”), i.e., saturation fields, between a pair of Co
100−x
Cr
x
layers across a ruthenium (Ru) non-magnetic spacer layer (where the Ru layer thickness was 8 Å for maximizing the value of AFC), as the amount of Co decreases in sandwich-type Co
100−x
Cr
x
(30 Å)/Ru (8 Å)/Co
100−x
Cr
x
(30 Å) structures, for x increasing stepwise from 0 to 20 (i.e., x=0, 5, 10, 15, and 20). As may be appreciated, the saturation fields, and therefore the strength of AFC, are readily obtained from the graphical plots of M(H) loops of
FIG. 2
from the change in slope of M(H) and is seen to steadily decrease with increase in the amount x of Cr alloying element of the CoCr ferromagnetic alloy layers.
Moreover, as is evident from
FIG. 3
, similar behavior is observed with CoCrPt ferromagnetic alloys, as in sandwich-type Co
100−x−y
Cr
x
Pt
y
(30 Å)/Ru/Co
100−x−y
Cr
x
Pt
y
(30 Å) structures, for x=0, 5, 10 and y=0 and 10 (again with the thickness of the Ru spacer layer adjusted to provide the greatest amount of AFC), wherein the AFC decreases with increase in the amount x of Cr and/or the amount y of Pt in the CoCrPt ferromagnetic alloys.
Accordingly, there exists a need for improved methodology for providing thermally stable, high areal recording density magnetic recording media, e.g., longitudinal media, with increased strength magnetic coupling between a pair of ferromagnetic layers separated by a non-magnetic spacer layer (such as of Ru), wherein each of the pair of ferromagnetic layers is formed of a ferromagnetic alloy composition similar to compositions conventionally employed in fabricating longitudinal magnetic recording media, which methodology can be implemented at a manufacturing cost compatible with that of conventional manufacturing technologies for forming high areal recording density magnetic recording media. There also exists a need for improved, high areal recording density magnetic media, e.g., in disk form, which media include at least one pair of magnetically coupled ferromagnetic alloy layers separated by a non-magnetic spacer layer, wherein each of the ferromagnetic layers is formed of a ferromagnetic alloy composition similar to composit
Girt Erol
Ristau Roger Alan
Rickman Holly
Seagate Technology LLC
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