Dynamic magnetic information storage or retrieval – General recording or reproducing – Thermomagnetic recording or transducers
Reexamination Certificate
2002-08-07
2004-06-01
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
General recording or reproducing
Thermomagnetic recording or transducers
C360S017000, C360S016000, C360S066000
Reexamination Certificate
active
06744583
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for forming a magnetic pattern in a magnetic recording medium used for a magnetic recording device, method for producing a magnetic recording medium, a magnetic recording medium and a magnetic recording device.
2. Discussion of Background
A magnetic recording device represented by a magnetic disk device (a hard disk drive) has widely been used as an external memory device for an information processing device such as a computer, and has recently been used as a recording device for recording dynamic images or a set-top box.
Generally, the magnetic disk device houses a single or plurality of magnetic disks and a recording/reproducing head. As the recording/reproducing head, a flying head is generally used wherein it moves above the magnetic disk at a constant flying height. Other than the flying head, the use of a contact head is proposed in order to make the distance to the medium closer.
The magnetic recording medium such as the magnetic disk is generally prepared by forming a NiP layer, a metal underlayer, a magnetic layer (a recording layer), a protective layer, a lubricant layer and so on on the surface of a substrate of aluminum alloy successively. Or, it is prepared by forming a metal underlayer, a magnetic layer (a recording layer), a protective layer, a lubricant and so on on the surface of a substrate such as glass successively. The magnetic recording medium includes a longitudinal magnetic recording medium and a perpendicular magnetic recording medium. In the longitudinal magnetic recording medium, longitudinal recording is generally carried out.
The tendency of making the magnetic disk more dense has been accelerated year by year, and various techniques for increasing the density have been proposed. For example, there is an attempt to increase the number of tracks by narrowing the space of information recording tracks. For example, a density of track of 100 ktpi or more is needed in order to realize 100 Gbit/inch
2
.
In each track, a controlling pattern for controlling synchronization and the position of the recording/reproducing magnetic head is formed. When the space of tracks is narrowed, it is necessary to make the magnetic pattern (hereinbelow, referred to as “the servo pattern”) used for controlling the position of the magnetic head dense in a radial direction of the disk, i.e., to form the magnetic pattern in more number, so as to conduct precise controlling.
Further, there is an increased demand to widen a data recording area to increase the data recording capacity by reducing the area other than that for recording data, namely, an area used for the servo pattern and gap portions between the servo areas and the data recording areas. For this purpose, it is necessary to increase an output of the servo pattern or to increase the accuracy of synchronization.
In the conventional technique, there has been widely used a method wherein an opening is formed in the vicinity of the head actuator of the drive (the magnetic recording device), a pin with an encoder is inserted into the opening to engage the actuator with the pin whereby the head is driven to a correct position to record the servo pattern. However, such method encountered difficulty in recording correctly the servo pattern because the position of the gravity center of the actuator was different from the position of the gravity center of a positioning mechanism, so that highly accurate track position control could not be obtained.
On the other hand, there is a proposed technique that laser beams are irradiated to a magnetic disk to deform locally the surface of the disk whereby projections and recesses are physically formed so that servo patterns of projections and recesses are produced. However, this technique had problems that the formed projections and recesses made the flying head unstable to affect adversely recording or reproducing information; laser beams having a large power was necessary in order to form the projections and recesses, thus being costly, and it took much time to form the projections and recesses one by one.
In view of the above, some servo pattern forming methods are proposed.
As an example, there is a method that a servo pattern is formed in a master disk having a magnetic layer of high coercive force, the master disk is brought to close contact with the magnetic disk, and an auxiliary magnetic field is applied from the outside whereby a magnetic pattern is printed (U.S. Pat. No. 5,991,104).
As another example, there is a method that a magnetic disk is previously magnetized along a certain direction; a soft magnetic layer having a high permeability and low coercive force is formed by patterning on a master disk, and the master disk is brought to close contact with the magnetic disk, and then, an external magnetic field is applied. The soft magnetic layer serves as a shield, and a magnetic pattern is printed to an unshielded area (see U.S. Pat. No. 3,869,711, EP915456 and “Readback Properties of Novel Magnetic Contact Duplication Signals with High Recording Density FD” (Sugita, R et. al, Digest of InterMag 2000, GP-06, IEEE).
In this technique, a master disk is used, and a magnetic pattern is formed in the magnetic disk by applying a strong magnetic field.
The intensity of a magnetic field generally depends on distances. When a magnetic pattern is recorded by applying a magnetic field, the boundary of the pattern is apt to be unclear due to a stray magnetic field. Accordingly, it is essential to bring the master disk to contact with the magnetic disk in order to minimize the stray magnetic field. As the magnetic pattern is finer, it is necessary to bring them close contact without any gap. Usually, the both members are press-contacted by using vacuum suction.
Further, the higher the coercive force of the magnetic disk is, the larger the magnetic field used for printing is, and accordingly, the stray magnetic field becomes large. Therefore, the perfect close contact is required.
Accordingly, the above-mentioned technique is easily applicable to a magnetic disk of low coercive force or a flexible floppy (trademark) disk which is easy to contact. However, it is very difficult to apply this technique to a magnetic disk for high density recording which has a coercive force of 3,000 Oe or more. Namely, in the magnetic disk comprising a hard substrate, there was a possibility that fine dust deposited thereon at the time of contacting closely whereby a defect was resulted in the magnetic disk, or an expensive master disk was damaged. In a case of a glass substrate, in particular, there was a problem that the deposition of dust might cause insufficient close contact, so that it might be impossible to conduct magnetic printing, or a crack was resulted in the magnetic disk.
On the other hand, in the technique described in Japanese Patent Application Nos. 2000-134608 and 2000-134611, a magnetic pattern is formed in a magnetic recording medium in the combination of heating a local portion and applying an external magnetic field. For example, a medium is magnetized previously in a certain direction; pulse-like energy beams or the like are irradiated to the medium through a patterned mask to heat the medium locally; an external magnetic field is applied while the coercive force of the heated area is reduced so that recording is conducted to the heated area by using the external magnetic field. Thus, a magnetic pattern is formed.
According to this technique, the recording is performed with a relatively weak external magnetic field because the coercive force is reduced by heating. Further, since the area for recording is limited to the heated area, and there is no possibility of recording to the area other than the heated area even when the magnetic field is applied thereto, a clear magnetic pattern can be recorded without bringing the mask to close contact with the medium. Accordingly, there is little possibility that the medium or the mask is damaged by the close contact and causing an increased defect i
Arita Youji
Ikeda Hiroyuki
Seo Yuzo
Colon Rocio
Hudspeth David
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