Stabilized recording media including coupled discontinuous...

Details Stabilized recording media including coupled discontinuous... Stabilized recording media including coupled discontinuous...

2001-10-09

2004-08-17

Rickman, Holly (Department: 1773)

Stock material or miscellaneous articles

Composite

Of inorganic material

C428S690000, C428S336000, C428S212000, C428S900000

Reexamination Certificate

active

06777112

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to high areal recording density magnetic recording media exhibiting enhanced thermal stability and increased signal-to-medium noise ratio (“SMNR”). The invention finds particular utility in the form of hard disks such as employed in high areal recording density magnetic data/information storage and retrieval devices and systems.
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 substrate
10
, typically of aluminum (Al) or an aluminun-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
10
-
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. For example, the SMNR may be increased by reducing the grain size of the recording media, as by utilization of appropriately selected seed and underlayer structures and materials, and by reduction of the thickness of the magnetic recording layer. 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, reduce and 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 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 the discontinuous character of each of the AFC-coupled ferromagnetic layers of the media Specifically, if the magnetic grains of the upper and lower magnetic layers are not grown in vertical alignment, or if they are not of equal size, the areas written in each of the pair of ferromagnetic layers may not coincide. In addition, the prior art approaches to media design fail to adequately take into account the significant effect on stability of magnetic recording media arising from interactions between magnetic grains.
Accordingly, there exists a need for improved methodology and structures for providing thermally stable, high areal recording density magnetic recording media, e.g., in the form of hard disks, with increased signal-to-media noise ratios (SMNRs), e.g., longitudinal media which methodology and media structures can be implemented/fabricated at a manufacturing cost compatible with that of conventional manufacturing technologies for forming high areal recording density magnetic recording media.
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 magnetic or anti-ferromagnetic coupling between spaced-apart pairs of ferromagnetic layers for enhancing thermal stability and increasing SMNR, while providing full compatibility with all aspects of conventional automated manufacturing technology. Moreover, manufacture and implementation of the present invention can be obtained at a cost comparable to that of existing technology.
DISCLOSURE OF THE INVENTION
An advantage of the present invention is an improved, high areal recording density magnetic recording medium having enhanced thermal stability.
Another advantage of the present invention is an improved, high areal recording density magnetic recording medium exhibiting an increase signal-to-medium noise ratio (“SMNR”).
Yet another advantage of the present invention is an improved, high areal recording density magnetic recording medium having enhanced thermal stability and SMNR arising from magnetic or anti-ferromagnetic coupling between spaced-apart continuous and discontinuous ferromagnetic layers.
Additional advantages and other features of the present invention will be set forth in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized as particularly pointed out in the appended claims.
According to one aspect of the present invention, the foregoing and other advantages are obtained in part by a magnetic recording medium having increased thermal stability and signal-to

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