Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2002-01-04
2004-02-10
Rickman, Holly (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S336000, C428S668000, C428S900000, C427S128000, C427S131000
Reexamination Certificate
active
06689497
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to very high areal density magnetic recording media exhibiting improved thermal stability, such as hard disks. More particularly, the present invention relates to longitudinal, anti-ferromagnetically coupled (“AFC”) magnetic recording media including improved spacer layers providing reduced or optimized lattice mismatch with 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
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.
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, 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 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 interface exchange energy density, J, between the ferromagnetic layer pairs being a key parameter in determining the increase in stability.
However, a drawback associated with the above-described approach is encountered when a number of materials, e.g., Ru, are utilized as the non-magnetic spacer layer for providing AFC between Co-based ferromagnetic layers, as are typically employed in the fabrication of high areal density magnetic recording media. Illustratively, the lattice constants of hexagonal close-packed (“hcp”) Ru are a=2.714Å and c=4.299 Å, which lattice constants are frequently much larger than the corresponding lattice constants of the typically employed hcp Co-based ferromagnetic layers. Thus, in order to obtain a desired crystallographic orientation (e.g., an in-plane alignment of the c-axis) and microstructure of the Co-based ferromagnetic layer(s) grown on the non-magnetic spacer layer, the mismatch between the lattice constants of the non-magnetic spacer layer and the Co-based ferromagnetic layers on opposite sides of the non-magnetic spacer layer must be adjusted, i.e., reduced or optimized, in order to obtain optimal or maximal performance of the AFC media.
Accordingly, there exists a need for improved methodology for providing thermally stable, high areal density magnetic recording media, e.g., longitudinal media, with large interface exchange energy density, J, optimal microstructure and crystallographic orientation (i.e., in-plane alignment of the c-axis), and reduced or optimized lattice mismatch between vertically separated ferromagnetic layers and a non-magnetic spacer layer (such as of a Ru-based material) providing anti-ferromagnetic coupling (AFC) of the ferromagnetic layers, wherein each of the 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 density magnetic recording media. There also exists a need for improved, high areal density magnetic recording media, e.g., in disk form, which media include at least one pair of anti-ferromagnetically 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 compositions conventionally utilized in longitudinal magnetic recording media (such as Co-based alloys) and the lattice mismatch between each of the ferromagnetic layers and the non-magnetic spacer layer is reduced or optimized, leading to improved thermal stability.
The present invention, therefore, addresses and solves problems attendant upon forming high areal recording density magnetic recording media, e.g., in the form of hard disks, which media utilize anti-ferromagnetic coupling between vertically spaced-apart pairs of ferromagnetic layers for enhancing thermal stability, while providing full compatibility with all aspects of conventional automated manufacturing technol
Rickman Holly
Seagate Technology LLC
LandOfFree
Stabilized AFC magnetic recording media with reduced lattice... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Stabilized AFC magnetic recording media with reduced lattice..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Stabilized AFC magnetic recording media with reduced lattice... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3317481