Dynamic magnetic information storage or retrieval – Record transport with head stationary during transducing – Disk record
Reexamination Certificate
2002-08-06
2004-12-21
Bernatz, Kevin M. (Department: 1773)
Dynamic magnetic information storage or retrieval
Record transport with head stationary during transducing
Disk record
C360S317000, C360S135000, C360S119050, C428S611000, C428S686000, C428S332000, C428S336000, C428S690000
Reexamination Certificate
active
06833975
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic recording medium used for perpendicular magnetic recording and a magnetic recording and reproducing apparatus.
2. Description of the Related Art
Perpendicular magnetic recording which enables high recording density by longitudinal recording has attracted attention in the field of magnetic recording. A single layer medium
71
shown in
FIG. 8A and a
double-layer medium
74
shown in
FIG. 8B
are known as a magnetic recording medium used for perpendicular magnetic recording.
A single layer medium
71
is formed by laminating a perpendicular magnetic recording layer
73
on a non-magnetic substrate
72
. A double-layer medium
74
is formed by laminating a soft magnetic layer
76
and a perpendicular magnetic recording layer
77
in that order on a non-magnetic substrate
75
. A protective layer and a lubricant layer (both of them are not shown) are formed on the perpendicular magnetic recording layer in both of cases of the single layer medium and the double-layer medium.
A reproducing head
78
is a shielded type magnetoresistance effect element head. A pair of shielding layers
79
a
,
79
b
are provided so as to sandwich a non-magnetic layer
81
and a magnetoresistance effect element
80
is disposed at a part of the non-magnetic layer
81
between the shielding layers
79
a
and
79
b.
A recording head is not shown. Nevertheless, as a magnetic field component (perpendicular component) in a thickness direction of the perpendicular magnetic recording layers
73
and
77
is required, a head having a main magnetic pole to obtain larger perpendicular component of recording magnetic field is used instead of a ring type recording head used in an longitudinal recording medium.
The single layer medium and the double-layer medium respectively have advantages and disadvantages for recording and reproducing.
The double-layer medium is superior to the single layer medium for recording in a magnetic recording medium for perpendicular magnetic recording. The reason is as follows. Namely, in accordance with the double-layer medium, as a result of soft magnetic layer taking in lines of magnetic force from a main magnetic pole in unillustrated recording head, the lines of magnetic force from the main magnetic pole act on the perpendicular magnetic recording layer with larger perpendicular component. That is to say, the soft magnetic layer amplifies the perpendicular component of recording magnetic field in the perpendicular magnetic recording layer.
Nevertheless, the single layer medium is superior to the double-layer medium for reproducing the magnetic recording medium for perpendicular magnetic recording. In accordance with the double-layer medium, because the soft magnetic layer is provided, a signal magnetic field loop from a recording magnetization of perpendicular magnetic recording layer is extended, so that a resolution of reproduction is decreased.
The signal magnetic field loop from recording magnetization of the perpendicular magnetic recording layer is large in a case of the double-layer medium with the soft magnetic layer and is small in a case of the single layer medium without the soft magnetic layer. This is because the soft magnetic layer extends the signal magnetic field loop. Extension of the signal magnetic field loop decreases a resolution of reproduction. In order to increase the resolution of reproduction, it is ideal to pick up only the signal magnetic field loop from the recording magnetization immediately below the magnetoresistance effect element
80
.
In a case of the single layer medium
71
, as shown in
FIG. 9A
, a signal magnetic field loop
92
from a recording magnetization
91
which is apart from an area immediately below the magnetoresistance effect element
80
is not so extended. This is because the soft magnetic layer is not provided. The signal magnetic field loop
92
enters the shielding layer
79
a
and circulates to the recording magnetization
91
without passing through the magnetoresistance effect element
80
. That is to say, the magnetoresistance effect element
80
does not pick up the signal magnetic field loop from the recording magnetization
91
placed apart from an area immediately below the magnetoresistance effect element
80
. The resolution of reproduction is high from this standpoint.
On the other hand, in a case of the double-layer medium
74
, as shown in
FIG. 9B
, a signal magnetic field loop
94
from a recording magnetization
93
of perpendicular magnetic recording layer
77
is extended because of soft magnetic layer
76
. The signal magnetic field loop circulates via the shielding layer
79
a
, the magnetoresistance effect element
80
, the perpendicular magnetic recording layer
77
and the soft magnetic layer
76
to the recording magnetization
93
. As a result of the signal magnetic field loop
94
being extended, the signal magnetic field loop
94
from the recording magnetization
93
at an area spaced apart from an area immediately below the magnetoresistance effect element
80
is picked up by the magnetoresistance effect element
80
. This leads to a decrease in the resolution of reproduction.
FIG. 10
shows linear recording density dependency of reproduced output. With respect to a unit of linear recording density, i.e., “kFCI”, “k” indicates 10
3
and “FCI” indicates Flux Change per Inch. A reproduced output obtained when the linear recording density is 100 kFCI in the double-layer medium is standardized as “1”. A characteristic curve of the double-layer medium has large rate of change and a characteristic curve of the single layer medium has small rate of change. Larger reproduced output is preferable but in order to improve the resolution of reproduction, it is preferable that not the reproduced output but a rate of change is smaller. An output halving recording density D
50
which is a representative example of linear recording density resolution indicates a linear recording density at 50% of peak value of reproduced output. The output halving recording density D
50
of the double-layer medium is 510 kFCI (which is a value corresponding to 0.5, i.e., a half of peak value 1). In contrast, the output halving recording density D
50
of the single layer medium is 630 kFCI (which is a value corresponding to 0.27, i.e., a half of peak value 0.54). The output halving recording density D
50
of the single layer medium is larger than that of the double-layer medium. A resolution of reproduction of the single layer medium is superior to that of the double-layer medium.
With respect to a bit of recording magnetization in the perpendicular magnetic recording layer, upward or downward unit recording magnetization is determined as one bit (the shortest bit). As the number of unit recording magnetizations continued in the same direction is increased, long bit length is provided. On the other hand, the number of unit recording magnetizations is decreased, short bit length is provided. Namely, the larger the linear recording density is, the shorter the bit length is.
An influence of magnetic saturation of the magnetoresistance effect element is small in a case of the single layer medium because the signal magnetic field loop is small. In a case of the double-layer medium, the influence is exhibited because the signal magnetic field loop is extended. Still, in a case of shorter bit length, signal magnetic field loops reaching the magnetoresistance effect element
80
are alternately orientated and offset each other, so that the influence is not exhibited. In a case of longer bit length, signal magnetic field loops reaching the magnetoresistance effect element
80
are oriented in the same direction, so that the magnetoresistance effect element is easily saturated. This is shown in FIG.
10
. Namely, closer to longer bit length side, i.e., lower linear recording density side, the reproduced output becomes significantly larger in the double-layer medium. If saturation occurs, a reproduced signal is deteriorated. Magnetic satur
Ahagon Akira
Fukazawa Toshio
Sakaguchi Masaya
Bernatz Kevin M.
Matsushita Electric - Industrial Co., Ltd.
McDermott Will & Emery LLP
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