Stock material or miscellaneous articles – Structurally defined web or sheet – Including components having same physical characteristic in...
Reexamination Certificate
2001-12-20
2003-07-15
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including components having same physical characteristic in...
C428S336000, C428S690000, C428S690000, C428S900000, C360S097010
Reexamination Certificate
active
06592976
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to perpendicular magnetic recording medium which are small in read back noise and suitable for high-density magnetic recording, and to a magnetic recording apparatus using these media.
BACKGROUND OF THE INVENTION
The currently used practical magnetic recording system is the longitudinal magnetic recording system in which magnetic recording is made in parallel to the surface of the magnetic recording medium, and so that the magnetic N-poles are opposed one to one and that the magnetic S-poles are opposed to one to one. In order to increase the linear recording density in the longitudinal magnetic recording, it is necessary that the coercivity be increased by decreasing the product of residual flux density (Br) and magnetic film thickness (t) of the magnetic film of a recording medium to reduce the effect of the demagnetizing field at the magnetic recording process. In addition, to decrease the medium noise caused by magnetization transition, it is necessary to orient the magnetic easy axis of the magnetic film in the direction parallel to the substrate surface, and to control the crystal grain size. To control the crystal orientation and grain size of the magnetic thin film, an underlayer for structure control is formed between the substrate and the magnetic film.
As the magnetic film, a Co-based alloy thin film is used which chiefly contains cobalt Co, and has an element such as Cr, Ta, Pt, Rh,.Pd, Ti, Ni, Nb, Hf added to the cobalt. The Co-based alloy of the magnetic thin film is chiefly made of a material of hexagonal closed packed structure (hereinafter, referred to as hcp structure). The magnetic easy axis is present in the directions of c-axis, <0, 0.1> and is oriented in the longitudinal direction. An underlayer for structure control is formed between the substrate and the magnetic film in order to control the crystal orientation and grain size of the magnetic film. The underlayer is made of a material which chiefly contains Cr and has an element of Ti, Mo, V, W, Pt, Pd added to Cr. The magnetic thin film is formed by vacuum evaporation or sputtering. As described above, the product of residual flux density (Br) and magnetic film thickness (t) of the magnetic film is required to be reduced in order to reduce the medium noise in the longitudinal magnetic recording and to thereby increase the linear recording density. For this purpose, it has been considered that the magnetic film thickness is reduced to 20 nm or below, and that the crystal grain size is greatly reduced. However, such medium has a very important problem that the recording magnetization is reduced by thermal instability. This phenomenon interferes with the high density recording.
The presently used magnetic disk recording apparatus is of the longitudinal magnetic recording system. The technical subject is that the longitudinal domains parallel to the substrate are formed at high density in the longitudinal magnetic recording medium which is easy to be magnetized in the direction parallel to the disk substrate surface. A method of increasing the recording density in the longitudinal magnetic recording medium is proposed, which employs keepered media formed by depositing an extremely thin soft magnetic film on the recording medium that have the magnetic easy axis in the longitudinal direction.
This technique is described in Abstracts, page 116 (paper No. DQ-13) and pages 133-134 (paper No. EB12) published in the 41st Annual Conference on Magnetism & Magnetic Materials (Nov. 12-15, 1996).
In such documents, it is described that if this media structure is employed it will be possible to increase the longitudinal magnetic recording density to 1 Gb/in2 or above by use of thin film heads of self-recording/reproduction system. In the longitudinal recording system, however, since the adjacent recorded bits are substantially magnetized to oppose to each other, magnetization transition regions of certain widths are formed across the boundaries even when this technique is employed. Thus, it will be technically difficult to record at a longitudinal density of 5 Gb/in2 or above.
On the other hand, the perpendicular magnetic recording system forms domains on the recording medium surface perpendicularly, and so that the adjacent recorded bits are unti-parallel to each other. This system has the advantage that the demagnetizing field at the boundary between the recorded bits is decreased, and thus it is one of the powerful means for high-density magnetic recording.
For the longitudinal high-density recording, it is necessary that the magnetic film be formed to have a thickness of 20 nm or below as described above. In this case, there is a problem that the recorded magnetization regions may be lost by thermal instability. On the contrary, the perpendicular magnetic recording system is able to form the magnetic film thicker than the longitudinal magnetic recording system, and thus stably maintain the recorded magnetization regions. In order to reduce the media noise generated from the magnetization transition and increase the linear recording density in the perpendicular recording system, it is necessary to orient the magnetic easy axis of the magnetic film perpendicularly to the substrate surface, and control the crystal grain size.
As the magnetic film, a Co-based alloy thin film is used which chiefly contains cobalt Co and has an element of Cr, Ta, Pt, Rh, Pd, Ti, Ni, Nb, Hf added to Co. The Co-based alloy of the magnetic thin film is chiefly made of a material of hexagonal closed packed structure (hereinafter, referred to as hcp structure). The magnetic easy axis is present in the directions of c-axis, <0, 0.1> and is oriented in the perpendicular direction. The magnetic thin film is formed by vacuum evaporation or sputtering. In order to increase the linear recording density at the time of recording and the read output and reduce the read back noise so that the magnetic recording characteristics can be improved, it is necessary to improve the perpendicular orientation of the c-axis of the Co-based alloy thin film and control the crystal grain size. Thus, it has so far been considered that an underlayer for structure control is formed between the substrate and the magnetic film.
The perpendicular magnetic recording system has attracted a great deal of attention as a system capable of high-density magnetic recording, and structure of medium suitable for the perpendicular magnetic recording have been proposed. A method of providing a non-magnetic underlayer between the perpendicular magnetization film and the substrate has been examined in order to improve the perpendicular orientation of the perpendicularly magnetized film made of a Co-based alloy material. For example, a method of depositing a Ti film as an underlayer for a Co—Cr magnetic film is described in JP-A-5877025, and JP-A-58-141435, a method of providing an under layer made of Ge, Si material in JP-A-60-214417, and a method of providing an underlayer made of an oxide material such as CoO, NiO in JP-A-60-064413. In addition, a magnetic recording medium having a soft magnetic layer of Parmalloy provided between the substrate and the perpendicular magnetization film has been considered as a perpendicular magnetic recording medium which is used in combination with a single-pole type magnetic recording head.
However, in order to achieve ultra-high density magnetic recording of several Gb/in
2
or above, particularly more than 10 Gb/in
2
, it is important to reduce the noise contained in the read output signal, particularly the medium noise caused by the micro-structure of the medium in addition to the improvement of the linear recording density. Thus, it is necessary to more highly control the thin film structure in addition to the crystal orientation of the magnetic film. The media noise has so far been tried to reduce by various ways. For example, these ways are (1) to segregate the nonmagnetic element Cr of CoCr-based alloy in the crystal grain boundary or grains in order to suppress the magnetic mu
Futamoto Masaaki
Hirayama Yoshiyuki
Honda Yukio
Inaba Nobuyuki
Ito Kenya
Kenyon & Kenyon
Resan Stevan A.
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