Dynamic magnetic information storage or retrieval – General recording or reproducing – Thermomagnetic recording or transducers
Reexamination Certificate
2001-05-15
2004-08-24
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
General recording or reproducing
Thermomagnetic recording or transducers
C360S055000, C360S097010, C360S135000
Reexamination Certificate
active
06781779
ABSTRACT:
The present invention relates to a magnetic recording medium and its production method and a magnetic recording apparatus. Particularly, it relates to a magnetic recording medium carrying out recording and reproducing by a flying/contact magnetic head and its production method and a magnetic recording medium.
A magnetic recording apparatus represented by a magnetic disk apparatus (hard disk drive) has been widely used as an outboard recording apparatus of an information processing apparatus such as a computer, and in recent years, it has been used also as a recording apparatus for dynamic images or as a recording apparatus for a set-top box.
A magnetic disk apparatus usually consists of a shaft which fixes one or plurality of magnetic disks in a skewered state, a motor which is bonded to said shaft by means of a bearing and which rotates the magnetic disk, a magnetic head which is used for recording and/or reproducing, an arm to which said head is attached, and an actuator capable of moving the head to an optional position on the magnetic recording medium by means of the head arm. The head for recording and reproducing is usually a flying head, and moves on the magnetic recording medium with a certain flying height.
Further, in addition to the flying head, use of a contact head has also been proposed so as to further shorten the distance from the medium.
The magnetic recording medium to be mounted on the magnetic disk apparatus is prepared usually by forming a NiP layer on the surface of a substrate made of e.g. an aluminum alloy, conducting a required smoothing treatment, texturing treatment or the like, and subsequently forming e.g. a metal base layer, a magnetic layer (information recording layer), a protective layer and a lubricant layer thereon. Otherwise, it may be formed by subsequently forming e.g. a metal base layer, a magnetic layer (information recording layer), a protective layer and a lubricant layer on the surface of a substrate made of e.g. glass. As the magnetic recording medium, a longitudinal magnetic recording medium and a perpendicular magnetic recording medium are mentioned. On the longitudinal magnetic recording medium, longitudinal recording is usually conducted.
The protective layer on the magnetic layer prevents damages of the magnetic layer due to impact of the flying magnetic head or sliding of the contact head, and the lubricant layer imparts lubricity between the magnetic head and the medium. By the present constitution, recording and reproducing by a flying/contact magnetic head becomes possible. Use of a flying/contact head can shorten the distance between the magnetic layer and the head, whereby information recording with a significantly high density becomes possible as compared with an optical disk or a photomagnetic disk employing a head of another type.
The density of the magnetic recording medium becomes high acceleratingly year by year, and the density becomes high by an annual rate of at least 60% in recent years. Many technique may be mentioned to realize this high density, and it is attempted, for example, to employ a GMR head as a magnetic head which is a magnetic head having its flying height decreased, to improve the magnetic material to be used for a recording layer of the magnetic disk, or to shorten the space between information recording tracks in the magnetic disk.
In each track, a magnetic pattern for control which controls the magnetic head, such as a signal to be used for position control of the magnetic head or a signal to be used for synchronous control, is formed. If the space between the information recording tracks is shortened to increase the number of tracks, signals to be used for position control of the data recording/reproducing head (hereinafter sometimes referred to as servo signals) have to be dense relative to the radius direction of the disk correspondingly, i.e. more signals have to be provided to carry out precise control.
Further, it is also strongly required to decrease the region other than the region to be used for data recording, i.e. the region used for the servo signals and the gaps between the servo region and the data recording region, in order to enlarge the data recording region and to increase the data recording capacity. Accordingly, it is necessary to increase output of the servo signals and to increase precision of the synchronous signals.
A method which has been used widely as a servo signal forming method is to make a hole in the vicinity of a head actuator of a drive (magnetic recording apparatus), insert a pin equipped with an encoder to the hole, engage said pin with the actuator, and drive the head to a precise position to record the servo signals. However, by this method, no higher precision than the limit of the recording by a magnetic head can be obtained.
Accordingly, as a magnetic printing method to a magnetic disk, a method of patterning a soft magnetic material to a master disk and contacting the master disk with a magnetic disk, which is used as a shield, and applying a magnetic field from the exterior to print the magnetic pattern, has been proposed (JP-A-50-60212 (U.S. Pat. No. 3,869,711), JP-A-10-40544 (European Patent No. 915456), “Readback Properties of Novel Magnetic Contact Duplication Signals with High Recording Density FD” (Sugita, R et. al, Digest of InterMag 2000, GP-06, published by IEEE)).
However, this method can be applied to a hard disk or a floppy disk having a low coercive force, but can hardly be applied to a magnetic disk having a high coercive force.
For example, the literature by Sugita et. al reports results of application of the magnetic printing method to a floppy disk and reports that excellent results of e.g. PW50 can be obtained. However, (1) the coercive force is 2,300 Oe and relatively low, and printing can be carried out with a small external magnetic field. Further, it is considered that conditions are suitable for magnetic printing, such that (2) a floppy disk has flexibility and is likely to be in contact with a master disk, (3) the magnetic pattern to be formed is broad with a width of 5 &mgr;m or 10 &mgr;m, and it is easy to improve PW50, and (4) a floppy disk usually has no protective layer, whereby magnetic printing can easily be carried out.
In recent years, the coercive force of a longitudinal hard disk exceeds 3 kOe. If the coercive force of a magnetic disk is large, a larger external magnetic field is required for magnetic printing, however, if the external magnetic field is made large, the magnetic field which leaks to the surrounding becomes significant, whereby the leakage magnetic field can not adequately be shielded at the pattern boundary. Accordingly, the magnetic transition region becomes unclear, and the signal quality such as PW50 may be impaired.
Further, it is very difficult to completely contact the master disk with the magnetic recording medium to which magnetic printing is applied, and the medium may have a flaw due to the contact.
On the other hand, with respect to a perpendicular hard disk which has been developed in recent years, it is difficult to shield it by the soft magnetic material, and accordingly, it is more difficult to apply the magnetic printing method.
Under these circumstances, it is an object of the present invention to provide a magnetic recording medium having improved precision and output of signals for control such as servo signals and synchronous signals, and a method for forming a magnetic pattern for control, and to provide a magnetic recording medium with which a high density recording can be carried out and a magnetic recording apparatus in a short period of time at a low cost.
According to a first aspect of the present invention, there is provided a magnetic recording medium for recording information by forming a magnetic pattern for information thereon by a magnetic head, which is a longitudinal magnetic recording medium having a coercive force of at least 3000 Oe, and which has a magnetic pattern for control of the magnetic head preliminarily formed thereon, wherein the full width at half maximum
Arita Yoji
Ikeda Hiroyuki
Hudspeth David
Matsushita Electric - Industrial Co., Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Rodriguez Glenda P
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