Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-08-30
2003-10-21
Rickman, Holly (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S212000, C428S690000, C428S900000
Reexamination Certificate
active
06635367
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic recording device for a household electrical information device such as a digital VTR or a magnetic disk drive used in a computer, an information processing device or the like, and a magnetic recording medium thereof, and more particularly to a magnetic recording medium ideal for realizing high density recording and a magnetic recording device using this magnetic recording medium.
2. Description of the Related Art
Semiconductor memories, magnetic memories and the like are used in the storage (recording) devices of information equipment. From the viewpoint of high speed access, semiconductor memories are used in internal storage devices, whereas from the viewpoint of high capacity, low cost and nonvolatilty, magnetic memories are used in external storage devices. Magnetic memories are used mainly in magnetic disk drives, magnetic tapes and magnetic card drives. To write magnetic information onto the recording medium, i.e. the magnetic disk, magnetic tape, magnetic card or the like, a magnetic recording part that generates a strong magnetic field is used. Moreover, to play back magnetic information that has been recorded at high density, a playback part that makes use of the phenomenon of magneto-resistance or the phenomenon of electromagnetic induction is used. Recently, giant magneto-resistive effects and tunnel type magneto-resistive effects have also started to be studied. The above functional parts (the magnetic recording part and the playback part) are provided on an input/output component called a magnetic head.
FIG. 10
shows the basic constitution of a magnetic disk drive. FIG.
10
(
a
) is a plan view of the drive, while FIG.
10
(
b
) is a cross-sectional view along the line A—A′ shown in FIG.
10
(
a
). A recording medium
101
is fixed to a rotating bearing
104
, and is rotated by a motor
100
.
FIG. 10
shows an example in which there are 5 magnetic disks and 10 magnetic heads (with 3 of the magnetic disks and 4 of the magnetic heads actually being depicted), but the number of magnetic disks and the number of magnetic heads may each be any number from 1 upwards. A magnetic head
102
moves across the surface of the rotating recording medium
101
. The magnetic head
102
is supported by a rotary actuator
103
via an arm
105
. A suspension
106
has a function of pushing the magnetic head
102
against the recording medium
101
with a prescribed load. Prescribed electrical circuits are needed for processing the playback signal and inputting and outputting information. PRML (partial response maximum likelihood) and EPRML (extended PRML) signal processing circuits that actively utilize waveform interference at high recording density have recently been introduced, and have contributed greatly to increased recording density. These circuits are installed in a case
108
or the like.
The parts provided on the magnetic head for recording and playing back information have, for example, a constitution as shown in FIG.
11
. The recording part
111
is composed of a spirally wound coil
116
, and magnetic poles
117
and
118
that envelop the coil
116
from the top and bottom respectively and are magnetically coupled to the coil
116
. The magnetic poles
117
and
118
are each composed of a patterned magnetic film. The playback part
112
is composed of a magneto-resistive effect element
113
, and an electrode
119
for passing a constant current through the magneto-resistive effect element
113
and detecting changes in the resistance. The magnetic pole
118
, which also serves as a magnetic shielding layer, is provided between the recording part
111
and the playback part
112
. A shielding layer
115
is also provided below the magneto-resistive effect element
113
. The shorter the length of the gap between the shielding layer
115
and the magnetic pole
118
(which also serves as a shielding layer), the higher the playback resolution. The functional parts described above are formed on top of a magnetic head slider
1110
.
To make the magnetic disk drive have a large capacity, the magnetic information recorded on the recording medium
101
shown in
FIG. 10
should be at high density. However, a conventionally used magnetic recording medium is composed of minute crystalline particles, and thus there is a problem that as the recording density is increased, the number of particles per bit becomes lower and hence noise increases. Attempts have thus been made to reduce noise by making the diameter of the magnetic particles lower, and promoting segregation by using a non-magnetic component at the boundaries between the magnetic particles to reduce the interactions between the magnetic particles. However, in recent years the recording density has been increased at a rate of over 50% per year, and attempts are now being made to carry out recording and playback at a surface recording density of about 15 Gb/in
2
or more, whereupon as the volume of the magnetic particles is reduced, decay of the recording magnetization due to thermal fluctuation (thermal demagnetization) becomes a serious problem. This is a phenomenon whereby the magnetization of the particles that make up the medium is reversed by heat, and becomes marked as the particle diameter is reduced to reduce noise. It is hoped that the influence of thermal fluctuation can be mitigated using the perpendicular magnetic recording method proposed by Iwasaki et al. Moreover, at the 2000 Intermag international conference, a longitudinal medium in which the magnetic layers are antiferromagnetically coupled through Ru (called an ‘AFC medium’) was proposed by Fujitsu and IBM as a way of enhancing thermal stability. However, with this newly proposed medium, the recording magnetic field becomes large, and it is thought that there is a high possibility that this will cancel out the merits of thermal stability enhancement. A description will now be given of the antiferromagnetically coupled (AFC) medium that forms the basis of the present invention, with reference to FIG.
3
.
FIG. 3
is a conceptual diagram of the cross-sectional structure of the medium. The medium comprises a magnetic underlayer
12
formed on top of a non-magnetic substrate
15
, and a recording magnetic layer
11
formed via a non-magnetic intermediate layer
13
. If Ru is used as the non-magnetic intermediate layer
13
, then exchange coupling takes place between the recording magnetic layer
11
and the magnetic underlayer
12
. The associated exchange coupling energy J varies in an oscillatory fashion with the thickness of the Ru non-magnetic intermediate layer
13
as shown in FIG.
4
. Exchange coupling takes place such that the magnetization direction of the recording magnetic layer
11
and the magnetization direction of the magnetic underlayer
12
are anti-parallel to one another when the exchange coupling energy J takes a negative value, and are parallel to one another when the exchange coupling energy J takes a positive value. By setting the thickness of the Ru non-magnetic intermediate layer
13
such that the exchange coupling energy J is at the negative peak, the magnetization of the recording magnetic layer
11
and the magnetization of the magnetic underlayer
12
can thus be coupled antiferromagnetically (i.e. made to be anti-parallel to one another) The product of the thickness and the residual magnetization of the recording magnetic layer
11
is made to be larger than the product of the thickness and the residual magnetization of the magnetic underlayer
12
. For the sake of simplicity, assume that the recording magnetic layer
11
and the magnetic underlayer
12
have the same saturation magnetization Ms and the same magnetic anisotropy energy Ku, and let the particle volume for the recording magnetic layer
11
be v
1
and the particle volume for the magnetic underlayer
12
be v
2
. When the antiferromagnetic coupling is sufficiently strong, the value of K&bgr;=Ku*v/(k*T) (where K is Boltzmann's constant and T is
Akagi Fumiko
Igarashi Masukazu
Tomiyama Futoshi
Zaitsu Hideki
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