Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2000-09-29
2003-07-22
Rickman, Holly (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S611000, C428S900000, C427S131000, C204S192150, C204S192200
Reexamination Certificate
active
06596417
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
Not Applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic thin film for a magnetic recording medium, and more particularly, to Ga
3
Pt
5
structured underlayers for use with a cobalt or cobalt based magnetic layer.
2. Description of the Invention Background
In recent years there has been an ever-increasing demand for computers with greater data storage capacity. This demand has been met by the development of computer discs, both flexible and rigid, that contain magnetic recording media with a greater magnetic recording density. Data on the discs is stored in circular tracks and divided into segments within the tracks. Disc drives typically employ one or more discs rotated on a central axis. A magnetic head is positioned over the disc surface to either access or add to the stored information. The heads for disc drives are mounted on a movable arm that carries the head in very close proximity to the disc over the various tracks and segments. The structure of disc drives is well known.
Presently, the dominant type of disk is a thin-film disk comprised of a multilayer structure that includes a substrate at the base covered by an underlayer structure, a magnetic layer structure and optionally, an overlayer at the top. The overlayer is commonly coated with an overcoat and an organic lubricant. Sometimes an intermediate layer will be placed between the underlayer structure and the magnetic layer and in addition sometimes a seed layer will be placed between the substrate and the underlayer structure. Data, in the form of magnetic bits, is stored on the magnetic layer. The magnetic layer is typically comprised of cobalt or a cobalt based alloy with a hexagonal closed packed (“HCP”) structure, such as CoCrTa, CoCrPt, CoCrPtB, CoCrPtTa, and CoNiCrPt.
The microstructure of the magnetic layer is critical to achieving a high magnetic recording density. For thin film longitudinal magnetic recording media, the desired crystalline structure of the Co or Co alloy is HCP with uniaxial crystalline anisotropy and a magnetization easy direction along the c-axis, which is in the plane of the film. The better the in-plane c-axis crystallographic texture, the more suitable the Co alloy thin film is for use in longitudinal recording.
To achieve a high magnetic recording density, the magnetic layer must consist of small and isolated grains that reduce media noise. In addition, a key to increasing media recording density is to reduce transition length, which can be achieved by increasing media coercivity. High coercivity is achieved by obtaining Co grains of such crystalline perfection that the Co magneto-crystalline anisotropy is maximized and not compromised by lattice strains and defects. It is well known that, by obtaining a good Co crystallographic texture, the alignment of the Co easy axis in the film plane increases the coercivity of the media. There are two crystallographic textures that align the Co easy axis in the thin film plane, Co (1120) and Co (1010).
The desired microstructure of the magnetic layer can be achieved by manipulating the deposition process, by grooving the substrate surface, or, most commonly, by using an underlayer. It is well known that an underlayer can be used to control the texture and grain size of the magnetic layer. Various materials have been employed for use as an underlayer. In particular, for longitudinal media, NiAl, NiP, Cr and Cr alloys containing such elements as Mn, Ru, Ti, W, Mo or V have been used, although, among these materials, pure Cr and Cr alloys have been the most widely used. A Cr underlayer develops a Cr (002) texture when deposited at elevated temperatures, e.g., about 150 or 200° C., which enables epitaxial growth of the Co (1120) textured thin film.
U.S. Pat. No. 5,693,426 to Lee et al., teaches the use of a material having a B2-ordered crystalline structure, and a combined layer structure of a B2 followed by a Cr or Cr alloy, as an underlayer structure. These B2 materials include NiAl, AlCo, FeAl, FeTi, CoFe, CoTi, CoHf, CoZr, NiTi, CuBe, CuZn, AlMn, AlRe, AgMg, and Al
2
FeMn
2
. The most preferable material is NiAl. The NiAl underlayer is preferable to the Cr underlayer because the unique NiAl (112) texture can be used to induce the uni-crystal Co layer of the Co (1010) texture. In addition, the NiAl underlayer induces smaller Co grains and a “tighter” grain size distribution than can be achieved with the Cr underlayer. Both of these factors are essential to reduce media noise.
Notwithstanding the benefits achieved by the use of materials having a B2-ordered crystalline structure as an underlayer, and NiAl in particular, the NiAl (112) plane is not the lowest surface-energy plane. There is a need for recording media having even greater storage density and improved texture of NiAl.
SUMMARY OF THE INVENTION
The present invention provides an improved recording media. The recording media of the invention may be used for incorporation in a disc drive having a rotatable disc for operation in conjunction with magnetic transducing heads for the recording and reading of magnetic data. It may also be used with storage devices such as flexible magnetic discs or tapes using known flexible substrates or x-y addressable storage systems that might use ridge substrates. The novel recording media comprises a flexible or rigid substrate, a magnetic layer, preferably formed from a Co or Co alloy film, and an underlayer comprised of a material having a Ga
3
Pt
5
structure disposed between the substrate and the magnetic layer. As used herein, Ga
3
Pt
5
structure means a material having a crystal symmetry like that of Ga
3
Pt
5
. The Ga
3
Pt
5
structure has orthorhombic symmetry. Materials having a Ga
3
Pt
5
structure include Ga
3
Pt
5
, Mn
3
Pd
5
, &dgr;Ga
3
Ni
5
, InPt
2
, and Ni
5
Al
3
. Ni
5
Al
3
, the most studied of the Ga
3
Pt
5
materials, is a crystallographic derivative of the face-centered cubic (“FCC”) structure. The underlayer may be formed in multiple layers wherein each layer is a different one of the foregoing FCC derivative materials, or wherein the layers alternate between a different one of the foregoing FCC derivative materials and a body-centered cubic (“BCC”) derivative material. The Co or Co alloy magnetic layer has a HCP structure deposited with its magnetic easy axis substantially parallel to the plane of the magnetic layer.
An overlayer that, in turn, may be covered by an overcoat may cover the magnetic layer. An organic lubricant is preferably added over the overcoat.
The recording medium may also include a first intermediate layer interposed between the magnetic layer and the underlayer. The first intermediate layer may be used to promote epitaxial crystalline growth of the magnetic layer. The first intermediate layer, if used, can consist of Cr, a Cr alloy, or a material having a BCC derivative crystalline structure, such as a material having a B2, DO
3
, or L2
1
crystalline structure. Cr has a BCC crystalline structure. A derivative structure of a basic structure is one in which one or more symmetry elements of the basic, or “parent”, structure (translational or orientational) is (are) suppressed. The basic periodicity and position of the atoms remains the same but the specific atomic occupancies change. BCC structures have many derivative structures, including but not limited to B2, DO
3
, or L2
1
. The BCC structure has two atoms in its unit cell. The occupancy of the atom at (000) and that at (½, ½, ½) is the same. The same can be seen to be true for the other examples of derivative structures. The degree of atomic order increases:for each crystal structure in the sequence of crystal structures from BCC to B2 to DO
3
to L2
1
. Examples of suitable materials for the first intermediate layer include NiAl, AlCo, FeAl, FeTi, CoFe, CoTi, CoHf, CoZr, NiTi, CuBe, CuZn, AlMn, AlRe, AgMg, Mn
3
Si and Al
2
FeMn
2
. When NiAl is used as the mat
Hsu Yu-Nu
Lambeth David N.
Laughlin David E.
Carnegie Mellon University
Kirkpatrick & Lockhart LLP
Rickman Holly
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