Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2000-08-14
2003-02-25
Rickman, Holly (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S213000, C428S336000, C428S900000, C204S192100, C204S192120, C204S192150, C204S192200
Reexamination Certificate
active
06524730
ABSTRACT:
TECHNICAL FIELD
The present invention relates to the recording, storage and reading of magnetic data, particularly rotatable recording media, such as thin film magnetic disks having smooth surfaces for data zone. The invention has particular applicability to high density recording media exhibiting low noise and having improved flying stability, glide performance and head-media interface reliability for providing zero glide hits.
BACKGROUND ART
The requirements for high areal density impose increasingly greater requirements on magnetic recording media in terms of coercivity, remanent squareness, low medium noise and narrow track recording performance. Data are written onto and read from a rapidly rotating recording disk by means of a magnetic head transducer assembly that flies closely over the surface of the disk.
It is considered desirable during reading and recording operations to maintain each transducer head as close to its associated recording surface as possible, i.e., to minimize the flying height of the head. This objective becomes particularly significant as the areal recording density increases. The areal density (Mbits/in
2
) is the recording density per unit area and is equal to the track density (TPI) in terms of tracks per inch times the linear density (BPI) in terms of bits per inch.
The increasing demands for higher areal recording density impose increasingly greater demands on flying the head lower because the output voltage of a disk drive (or the readback signal of a reader head in disk drive) is proportional to 1/exp(HMS), where HMS is the space between the head and the media. Therefore, a smooth recording surface is preferred, as well as a smooth opposing surface of the associated transducer head, thereby permitting the head and the disk to be positioned in closer proximity with an attendant increase in predictability and consistent behavior of the air bearing supporting the head.
In recent years, considerable effort has been expended to achieve high areal recording density. Among the recognized significant factors affecting recording density are magnetic remanance (Mr), coercivity, coercivity squareness (S*), signal
oise ratio, and flying height, which is the distance at which a read/write head floats above the spinning disk. Prior approaches to achieve increased areal recording density for longitudinal recording involve the use of dual magnetic layers separated by a non-magnetic layer as in Teng et al., U.S. Pat. No. 5,462,796, and the use of a gradient magnetic layer interposed between two magnetic layers as in Lal et al., U.S. Pat. No. 5,432,012.
However, the goal of achieving a rigid disk recording medium having an areal recording density of about 100 Gb/in
2
has remained elusive. In particular, the requirement to further reduce the flying height of the head imposed by increasingly higher recording density and capacity renders the disk drive particularly vulnerable to head crash due to accidental glide hits of the head and media. To avoid glide hits, an accurately controlled movement of the head and a smooth surface of data zone are desired.
It is extremely difficult to produce a magnetic recording medium satisfying such demanding requirements, particularly a high-density magnetic rigid disk medium for longitudinal and perpendicular recording. The magnetic anisotropy of longitudinal and perpendicular recording media makes the easily magnetized direction of the media located in the film plane and perpendicular to the film plane, respectively. The remanent magnetic moment of the magnetic media after magnetic recording or writing of longitudinal and perpendicular media is located in the film plane and perpendicular to the film plane, respectively.
In theory, perpendicular media is capable of considerably higher linear data density. Generally, this possibility stems from the fact that information is stored in perpendicular media in discrete domains having opposite magnetization to the magnetization found in the surrounding areas. Such domains can potentially reside in crystals in the media. Typically the information is read from the media through use of a magnetic head that converts local discontinuities present in the discrete domains of perpendicular magnetization into electrical fields which can then be processed as information.
However, between the discrete domains of magnetization, magnetization parallel to the surface of the media, or subdomains or opposite magnetization, are usually present. This is particularly true in situations where remanent magnetization of a layer is significantly smaller than the saturation magnetization of the media. In such situations, the transitions between the domains can cause undesirable electronic signals stemming from, essentially, magnetic noise.
Several terms that are important in describing magnetic recording media are explained below. Coercivity essentially refers to how firmly the media holds a particular orientation of magnetization. For example, how much energy is required to cause a crystal in the media to change orientation. On a magnetization hysteresis (M-H) curve, the required applied magnetic field to reduce the magnetization of the material to zero is called coercivity Hc. Permeability (&mgr;) is equal to B/H, where B is the flux density and H is the applied magnetic field.
The easy axis of magnetization of a crystal is the direction of spontaneous domain magnetization in the demagnetized state. The direction of the easy axis of magnetization can be detected on M-H curves. Along the easy axis of magnetization, the M-H curve is forms a square. Along the hard axis direction, the M-H curve is skewed.
Anisotropy refers to the energy stored in a crystal by virtue of the work done in rotating the magnetization of a domain of the crystal away from the easy axis of magnetization. Output basically refers to the strength of the flux created by the media to read the media. Media noise comes from the recording medium. When a magnetic pulse and a transition is written during recording, there is a noise when the signal is being readback.
Some materials change dimension when exposed to a magnetic field. This effect is called magnetostriction. Most NiFe compositions exhibit magnetostriction, except the composition of Ni
81
Fe
19
.
A multilayer superlattice has a structure with many interfaces of magnetic
on-magnetic layers. A bilayer superlattice [A/B]n has n bilayers stacked together to form a superlattice, e.g., [Co/Pt]n, [Co/Pd]n, [CoX/Pt]n, [CoX/Pd]n, where X=Cr, B, etc. The thickness of layers A and B can vary from about 3 Å to about 10 Å and from about 5 Å to about 20 Å, respectively.
A soft magnetic layer (also referred as “keeper layer”) is a layer on the substrate of a magnetic recording medium that gives better writing efficiency by pulling the magnetic flux down from the writing pole of a head of the magnetic recording medium. Soft magnetic layers are made of soft magnetic materials. Soft magnetic material is one of the two kinds of commonly available magnetic materials. One kind has a high coercivity and is called hard magnetic material, e.g., CoCr, CoCrTa and CoCrPt. Because it has high coercivity, it is “hard” to change the magnetization direction unless a strong reverse magnetic field is applied. Another kind is has a very low coercivity in the range of 0.1 Oe to 500 Oe and is called a soft magnetic material, e.g., NiFe, CoZrNb, FeAlNx. Because it has a low coercivity, it is easy (“soft”) to change the magnetization direction with a very small reverse magnetic field. “Hard” and “soft” magnetic materials in the context of this invention are not related to mechanical softness or hardness of the material.
In order to undertake perpendicular recording, it is necessary to utilize a magnetic recording media having perpendicular anisotropy. Perpendicular anisotropy is essentially due to a crystal structure of the magnetic material that creates a magnetic moment perpendicular to the surface of the media. One typical perpendicul
Morrison & Foerster / LLP
Rickman Holly
Seagate Technology LLC
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