The present invention generally relates to perpendicular magnetic recording and reproducing systems, and more particularly to a perpendicular magnetic recording and reproducing system which realizes satisfactory perpendicular magnetic recording and reproducing characteristics.
Generally, when recording and reproducing a signal on and from a magnetic recording medium by use of a ring core head as a magnetic head, the ring core head magnetizes a magnetic layer of the magnetic recording medium in a longitudinal direction of the magnetic recording medium (that is, in an in-plane direction) at the time of the recording and picks up the recording at the time of the reproduction. However, according to such a longitudinal magnetic recording system, it is known that the demagnetization field becomes high as the recording density increases and the demagnetization field introduces undesirable effects to the high density magnetic recording. Hence, in order to eliminate the undesirable effects of the demagnetization, a perpendicular magnetic recording system has been proposed in which the ring core head magnetizes the magnetic layer of the magnetic recording medium in a direction perpendicular to the magnetic layer. According to the perpendicular magnetic recording system, the demagnetization field becomes low as the magnetic recording density increases, and theoretically, it is possible to realize a satisfactory high density magnetic recording in which there is no decrease in the remanent magnetization.
As a conventional perpendicular magnetic recording medium which is used in the perpendicular magnetic recording system, there is a perpendicular magnetic recording medium having a cobalt-chromium (Co--Cr) film formed on a base film by a sputtering process. As is well known, the Co--Cr film is extremely suited for use in the perpendicular magnetic recording medium because the Co--Cr film has a relatively high saturation magnetization (Ms) and favors magnetization in a direction perpendicular to the Co--Cr film (that is, the coercivity in the direction perpendicular to the Co--Cr film is large and the axis of easy magnetization is perpendicular to the Co--Cr film).
However, when the ring core head performs the perpendicular magnetic recording and reproduction with respect to the perpendicular magnetic recording medium having the sputtered Co--Cr film, it is impossible to concentrate the magnetic flux at a predetermined magnetic recording position on the perpendicular magnetic recording medium, and there is a disadvantage in that it is impossible to obtain a strong magnetization which is in the direction perpendicular to the Co--Cr film and does not spread in the longitudinal direction of the perpendicular magnetic recording medium. In other words, when the ring core head is used to perform the recording on the Co--Cr film of the perpendicular magnetic recording medium, the magnetization direction easily deviates in the longitudinal direction of the perpendicular magnetic recording medium since the magnetic field generated by the ring core head includes considerable components in the in-plane direction. Accordingly, in order to maintain the magnetization direction in the perpendicular direction, the perpendicular magnetic recording medium must have a high perpendicular anisotropic magnetic field and have a saturation magnetization which is suppressed to a certain extent. However, the Co--Cr film does not have such characteristics, and there is a disadvantage in that it is impossible to perform a satisfactory perpendicular magnetic recording by the ring core head. In addition, the coercivity in the perpendicular direction must be large in order to obtain a high reproduced output from the perpendicular magnetic recording medium having the Co--Cr film. On the other hand, it is desirable to make the thickness of the perpendicular magnetic recording medium large in order to decrease the demagnetization field, but the perpendicular magnetic recording medium will not make contact with the ring core head in a satisfactory state when the thickness of the perpendicular magnetic recording medium is large because the perpendicular magnetic recording medium will lose its flexibility and become rigid. In this case, there are disadvantages in that the rigid perpendicular magnetic recording medium is easily damaged and undesirable effects are introduced to the ring core head, and it is impossible to perform a satisfactory perpendicular magnetic recording and reproduction.
Accordingly, a perpendicular magnetic recording medium having a double film construction has been proposed. According to this perpendicular magnetic recording medium, a film having a high permeability, that is, a film having a low coercivity such as a nickel-ion (Ni--Fe) film, is formed between the Co--Cr film and the base film. The magnetic flux which is spread within the high permeability film is concentrated toward the magnetic pole of the ring core head at a predetermined magnetic recording position in order to obtain a strong magnetization which is in the perpendicular direction and does not spread in the longitudinal direction of the perpendicular magnetic recording medium. However, in the case of the perpendicular magnetic recording medium having the double film construction, the coercivity of the high permeability film is extremely small compared to the coercivity of the Co--Cr film, and there is a disadvantage in that Barkhausen noise is generated. For example, the coercivity of the Co--Cr film is over 700 Oe, and the coercivity of the high permeability film is under 10 Oe. Further, in order to produce the perpendicular magnetic recording medium having the double film construction, an amorphous (ion-nickel) Fe--Ni alloy or the like is formed on the base film by a sputtering process under a predetermined sputtering condition suited for forming the high permeability film, and Co--Cr is thereafter formed on the high permeability film by a sputtering process under a certain sputtering condition suited for forming the Co--Cr film. As a result, the sputtering condition under which the sputtering process is performed and the target must be changed for the formation of each film, and the sputtering processes cannot be performed continuously. Therefore, there are disadvantages in that the processes of manufacturing the perpendicular magnetic recording medium are complex and unsuited for mass production.
On the other hand, as the magnetic which is used in the perpendicular magnetic recording and reproducing system, there are in addition to the ring core head an auxiliary pole type (or driven) perpendicular magnetic head (hereinafter simply referred to as an auxiliary pole type head) having an auxiliary magnetic pole opposing a main magnetic pole and a single-sided main pole type (or driven) perpendicular magnetic head (hereinafter simply referred to as a single-sided main pole type head) not requiring an auxiliary magnetic pole and having a main magnetic pole opposing only one surface of the perpendicular magnetic recording medium. However, in the case of the perpendicular magnetic recording and reproducing system using the auxiliary pole type head, the perpendicular magnetic recording medium must be inserted between the main and auxiliary magnetic poles of the auxiliary pole type head, and the application of the system is limited. In other words, there is a disadvantage in that it is difficult to employ the auxiliary pole type head in a recording and reproducing apparatus such as a video tape recorder and a hard disc player. On the other hand, in the case of the single-sided main pole type head, the disadvantage of the auxiliary pole type head is eliminated, however, the construction of the single-sided main pole type head becomes complex. Furthermore, the single-sided main pole type head is disadvantageous in that the magnetic field distribution cannot be directed in the perpendicular direction as much as the auxiliary pole type head.