The present invention relates to a magnetic transfer method for transferring a recording information to a magnetic recording medium used in a large capacity and high recording density magnetic recording and reproducing system. In particular, the invention relates to a magnetic transfer method to be used in the recording of servo signal, address signal, other normal video signal, audio signal, data signal, etc.
With rapid propagation and progress in the technique to utilize digital image, the amount of information processed by devices such as personal computer has extensively increased. To cope with the increase of the amount of information, there are now strong demands on a magnetic recording medium, which has large capacity for information recording and is available at low cost, and further, can record and read within shorter time.
In a high density recording medium, e.g. hard disk or large capacity removable type magnetic recording medium such as ZIP (Iomega Inc.), the information recording region has narrower tracks compared with floppy disk. In order to accurately scan the magnetic head with narrower track width and to record and reproduce signals at high S/N ratio, it is necessary to perform accurate scanning by using tracking servo technique.
In a large capacity magnetic recording medium such as hard disk or removable type magnetic recording medium, there are provided regions where servo signal for tracking, address information signal, reproduction clock signal, etc. are recorded at a given angular spacing. The magnetic head reproduces these signals at a given spacing and accurately scans on the track while confirming and correcting the position of the head. These signals are recorded on the magnetic recording medium in advance by the so-called “preformat” process when the magnetic recording medium is manufactured.
Accurate positioning is required for recording of servo signal for tracking, address information signal, reproduction clock signal, etc. In this respect, after the magnetic recording medium is incorporated in the drive, the preformat recording is performed by the magnetic head under strict position control using a special-purpose servo recording system.
However, in the preformat recording of servo signal, address signal, and reproduction clock signal, recording is performed under strict position control of the magnetic head using a special-purpose servo recording system, and this means that much time is required for the preformat recording. Also, magnetic recording density is increased and the amount of signals to be recorded by the preformat recording is also increased, and this means that much more time is required. The percentage of the cost required for the preformat recording process of servo signal in the total manufacturing cost of the magnetic recording medium is increased, and there are now strong demands on the reduction of the cost in this process.
On the other hand, a method is proposed, by which magnetic transfer of a preformat information is performed from the master carrier to the slave medium without recording the preformat information track by track. For instance, JP-63-183623 and EP-0915456 (JP-10-040544, JP-10-269566) describe such transfer technique.
According to the methods described in JP-63-183623 or EP-0915456, surface irregularities (i.e. convex and concave portions) corresponding to an information signal are formed on the surface of a substrate used as a master carrier for magnetic transfer, and a ferromagnetic thin film is formed at least on the surface of convex portions among the surface irregularities of the master carrier for magnetic transfer. The surface of the master carrier is brought into contact with the surface of a sheet-type or a disk-type magnetic recording medium where a ferromagnetic thin film or a coating layer of a composition containing ferromagnetic powder is formed. Or, AC bias magnetic field or DC magnetic field is applied on the surface, and the ferromagnetic material on the surface of the convex portions is excited. Thus, a magnetization pattern corresponding to the surface irregularities (convex and concave portions) is recorded on the magnetic recording medium. According to this method for magnetic transfer, the surface of convex portions of the master carrier for magnetic transfer is brought into close contact with the magnetic recording medium to be preformatted, i.e. the slave medium, and the ferromagnetic material of the convex portions is excited. Then, a predetermined preformat information is recorded on the slave medium. By this method, static recording can be achieved without changing relative positions of the master carrier and the slave medium, and accurate preformat recording can be performed. Also, this method is characterized in that the time required for the recording is very short.
This magnetic transfer method is a method to transfer by bringing the master carrier for magnetic transfer and the slave medium in stationary condition. In this respect, damage occurs less frequently on the master carrier and the slave medium in the process for recording the servo signal, and this method is considered as a method to provide high durability.
As the magnetic material used for the master carrier for magnetic transfer, a soft magnetic material is used. Initially, it has been believed that magnetic permeability of the magnetic layer gives extensive influence on the transfer property, and the priority has been given on high magnetic permeability when the material is selected. However, signal quality is in marginal region, and it is necessary to improve the signal quality further. Also, transfer magnetic field intensity region where magnetic transfer of the signal of good quality can be accomplished is very narrow, and there are problems relating to the facilities.
It is an object of the present invention to provide a magnetic transfer method, by which it is possible to increase the quality of the signal transferred when a recording information recorded on the carrier for magnetic transfer is transferred to the slave medium and which can provide extensive transfer magnetic field intensity region.