Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
2000-05-18
2002-05-28
Dinh, Tan (Department: 2653)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
C369S013130, C369S112010
Reexamination Certificate
active
06396776
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a recording/reproducing head, a recording/reproducing disk drive and a method for fabricating a magnetic sensor, which are used for a magnetic recording with heating a recording part by light irradiation (Optically Assisted Magnetic (OAM) recording) and reproducing by a magnetic sensor. More particularly, the invention relates to a recording/reproducing head, the recording/reproducing disk drive and a method for fabricating the magnetic sensor, which enable high density recording and high rate data transfer.
2. Description of the Prior Art
For use with hard disk drives (HDD),which perform recording and/or reproducing on magnetic recording films with a magnetic head, magnetoresistive (MR) sensors using magnetoresistance for reproduction or giant-magnetoresistive (GMR) sensors with higher sensitivity and higher resolution (these sensors are collectively referred to as magnetic sensors) have been developed. The recording density has been increased approximately 60% a year in recent years. However, it has turned out recently that the surface density has a limit of approximately 30 Gbits/ (inch)
2
because of the super paramagnetic effect: the magnetization direction of a magnetic domain is inverted in the opposite directions by magnetization of adjacent magnetic domains due to thermal disturbance (R. L. White, Tech. Digest of MORIS'99, 11-A-03(1999) P.7).
The optically assisted magnetic (OAM) recording method is proposed as a promising solution to this problem. By this method, the recording is performed by applying magnetic fields and beam spots onto magnetic recording films or magneto-optic recording films and the reproducing is performed with a magnetic sensor such as GMR sensor. The recording is performed with heating a magnetic film by the irradiation of a laser beam for decreasing the magnetization strength of the magnetic films. This method allows recording on a magnetic film of high magnetization, so the magnetization inversion at room temperatures can be avoided. A conventional recording/reproducing disk drives adopting the OAM recording method is described in the literature, “Nikkei Electronics, No. 734, (99.1.11), P.35”, for example
FIG. 27
shows the recording/reproducing disk drive. The recording/reproducing disk drive
1
has: a semiconductor laser
2
that emits laser beams
3
; a polarized beam splitter
33
that separates the laser beam from the semiconductor laser
2
and reflected beam from the recording/reproducing disk
8
; a quarter wavelength plate
34
that converts the laser beam
3
from the semiconductor laser
2
to circular polarized beam; a condense lens
4
′ that condenses the laser beams
3
from the semiconductor laser
2
after passing through the polarized beam splitter
33
and the quarter wavelength plate
34
; a hemispherical solid immersion lens (SIL)
6
that condenses the laser beams
3
from the condense lens
4
′, incident from a hemispherical incident surface
6
a
, to form a beam spot
9
a
on a beam-condense surface
6
c
; a flying slider
12
that supports the SIL
6
; a coil
10
for modulating magnetic fields, provided in the circumference of the beam spot
9
a
of the flying slider
12
; and a magnetic sensor
11
comprising a GMR sensor.
By the recording/reproducing disk drive
1
, the information is recorded in following steps: the semiconductor laser
2
emits a laser beam
3
in a pulse shape; a beam spot
9
a
is formed on the beam-condense surface
6
c
of the SIL
6
by the condense lens
4
′; a near field wave
9
b
leaked from the beam-condense surface
6
c
irradiates a magneto-optic recording film
8
b
on the recording/reproducing disk
8
to heat the magneto-optic recording film
8
b
, and at the same time the information is recorded by applying a modulating magnetic field by a coil
10
corresponding to the information. This is referred to as laser-pumped modified field magnetic (LP-MFM) recording. The LP-MFM recording enables recorded mark to be formed shorter than the beam spot diameter. Information is reproduced by scanning the recording/reproducing disk
8
by the magnetic sensor
11
with a magnetic-resistive film used as a detection part. According to the recording/reproducing disk drive
1
, since the beam spot
9
a
can be reduced inversely proportional to the refractive index of the SIL
6
, minute magnetic domains of approximately 0.3 &mgr;m wide can be formed, so the higher recording density can be achieved.
FIG. 28
shows the above-described LP-MFM recording and the reproduction with the magnetic sensor
11
. The LP-MFM recording is performed, as shown in FIG.
28
. The laser beam
3
, which is turned on and off like a pulse to be adapted to a mark interval. The recording/reproducing disk
8
is moved in the track direction X relative to the magnetic sensor
11
. The information is recorded by inverting the direction of applied external magnetic fields corresponding to the basis of recording information. Since circular marks
81
recorded first on a recording track
80
are partially erased due to recording of the next inverted magnetic field, crescent recording marks
81
are formed in the tail of near field wave
9
b
as shown in FIG.
28
. Because the mark length L is determined only by a recording frequency and disk rotation speed, it can be reduced to the size of magnetic particles of the recording film
8
b
. by increasing the recording frequency.
However, according to the conventional recording/reproducing disk drive
1
, the detection part
11
a
of the magnetic sensor
11
has rectangular shape as shown in FIG.
28
. If the crescent marks
81
was scanned with the sensor
11
and the magnetic sensor proceeded to the mark
81
after passing above the central portion of the preceding mark
81
, the tail portion of the preceding mark
81
and the present mark
81
would overlapped. So the resolving power would be decreased when the output signal of the magnetic sensor
11
is reproduced on the basis of the reference level S. Further, the output signal of the magnetic sensor
11
is distorted because of the asymmetry between the preceding and following portion of a mark, so the jitter is increased, then the information cannot be correctly reproduced. This phenomenon becomes conspicuous by reducing the mark length L. Although minute recorded mark can be formed during recording, a recording density cannot practically be increased even by use of the LP-MFM recording method because of the limit of the reproducing resolution. The above-mentioned limit of the recording density also limits the transfer rate.
FIG. 29
shows the dependence of the output signals of the magnetic sensor on the mark length L, when the thickness (length in the track direction X) T of the detection part
11
a
of the magnetic sensor
11
is constant. In this example, the size of a beam spot is 0.2 &mgr;m and the length of the detection part
11
a
of the magnetic sensor
11
is 0.07 &mgr;m. As seen from this figure, when the mark length L becomes smaller than the size of the near field wave
9
b
, output signals is rapidly reduced. Since the jitter is increased at the same time, the reproducible mark length L actually becomes approximately 0.15 &mgr;m. Although the shorter marks
81
can be formed by LP-MFM recording and the thickness T of the detection part
11
a
of the magnetic sensor
11
is thin, these advantages cannot be effectively used.
SUMMARY OF THE INVENTION
The present invention provides a recording/reproducing head, a recording/reproducing disk drive which provide a high recording density and a high transfer rate, and a fabrication method of a magnetic sensor used for the head.
The present invention provides a recording/reproducing head, which records recorded mark on recording/reproducing disks by applying magnetic fields and irradiating near field wave and detects magnetic fields from the recorded mark with a magnetic sensor. The head includes a laser beam emitting unit that emits a laser beam, an optical sys
Dinh Tan
Fuji 'Xerox Co., Ltd.
Oliff & Berridg,e PLC
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