Dynamic magnetic information storage or retrieval – General recording or reproducing – Specifics of biasing or erasing
Reexamination Certificate
2002-10-01
2004-09-21
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
General recording or reproducing
Specifics of biasing or erasing
C360S110000, C360S125330, C324S244000, C324S249000, C324S260000
Reexamination Certificate
active
06795263
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic head utilizing a magneto-impedance effect by which the impedance of a sensing conductor is varied by application of a magnetic field, and a magnetic recording and reproducing apparatus using the magnetic head.
An example of a magnetic reproducing head in the prior art is described with reference to
FIG. 12A
, FIG.
12
B and FIG.
13
.
FIG. 12A
is a perspective view of a magnetic reproducing head (hereinafter referred to as the MI head) utilizing the magneto-impedance effect (MI effect) in the prior art, described in IEICE Technical Report MR95-80.
In
FIG. 12A
, a magneto-impedance effect detector (hereinafter referred to as the magnetic detector) in a MI head
61
is configured by placing a thin film sensing conductor
42
of an electrically conductive metal thin film between two soft magnetic cores
46
and
47
each having a width
43
approximately equal to the track width of a magnetic recording medium
53
. As shown in an enlarged view of
FIG. 12B
, the soft magnetic cores
46
and
47
are formed by alternately laminating permalloy films
44
and SiO2 films
45
.
When the MI head
61
reproduces a signal magnetization
54
recorded on the magnetic recording medium
53
, a high frequency carrier signal in the UHF band is applied from a high frequency oscillator
48
to the thin film sensing conductor
42
through a resistor
49
, thereby flowing a high frequency current
50
therethrough. Then, a voltage change caused by the magneto-impedance effect is detected across terminals
51
and
52
connected to respective ends of the thin film sensing conductor
42
. The easy magnetization axes of the soft magnetic cores
46
and
47
are initially oriented in a direction parallel to the width direction of the recording track of the magnetic recording medium
53
.
When there is no signal magnetization
54
on the magnetic recording medium
53
, a voltage of a high frequency carrier signal arises across the terminals
51
and
52
, and the voltage value is equal to the product of the high frequency current
50
and the impedance between these terminals
51
and
52
of the thin film sensing conductor
42
.
When there is a signal magnetization
54
on the magnetic recording medium
53
, the easy magnetization axes of the soft magnetic cores
46
and
47
deviate from their initial direction of orientation because of the presence of the signal magnetization
54
. As a result, the impedance across these terminals
51
and
52
of the thin film sensing conductor
42
decreases due to the magneto-impedance effect.
The high frequency carrier signal is amplitude-modulated according to the change in the impedance of the thin film sensing conductor
42
by the signal magnetization
54
on the magnetic recording medium
53
, and thereby the signal magnetization
54
is detected. The signal magnetization
54
on the magnetic recording medium
53
can be read out by demodulating the amplitude-modulated signal.
The detection sensitivity of the signal magnetization
54
on the magnetic recording medium
53
based on the magneto-impedance effect is much higher than the detection sensitivity based on the magnetoresistive effect. The MI head utilizing the magneto-impedance effect has the possibility of producing an output about 10 times as high as that of the known giant MR head utilizing magnetic resistance which is in the process of development.
FIG. 13
is a characteristic curve showing the change in the high frequency carrier signal level with respect to the magnetic field applied to the MI head
61
. In
FIG. 13
, the characteristic curve
56
is obtained by setting the frequency of the high frequency carrier signal at 1 GHz and varying the strength of DC magnetic field applied to the MI head
61
placed in the central portion of the known Helmholtz coil.
According to the characteristic curve
56
, the rate of change of the high frequency carrier signal level is small at and near the point where the applied magnetic field strength is zero. In order to modulate the high frequency carrier signal with a high degree of modulation with respect to the change in the magnetic field strength and to obtain a high frequency amplitude-modulated signal with a low distortion, it is desirable to give a DC bias magnetic field
55
biasing the magnetic field so as to use the linear portion of the characteristic curve
56
. In the above-mentioned MI head, a DC power supply
58
superimposes a DC current on the current of the high frequency carrier signal in order to produce the DC bias magnetic field
55
. By flowing this DC current through the thin film sensing conductor
42
, a DC magnetic field is generated to bias the magnetic field.
The change rate of the impedance of the sensing conductor caused by the magneto-impedance effect is proportional to the product of the frequency of the high frequency carrier signal applied to the sensing conductor and the rate of change of the magnetic permeability of the soft magnetic cores. In order to increase in the detection sensitivity by increasing the change rate of the impedance of the sensing conductor, permalloy films
44
having a large permeability change are used for the material of the soft magnetic cores
46
and
47
in the prior art MI head as mentioned above. A laminated film structure consisting of the permalloy films
44
interleaved with insulating SiO
2
films
45
is employed in order to suppress eddy currents at high frequencies. Further, the frequency of the high frequency carrier signal is set at several hundred MHz or higher.
BRIEF SUMMARY OF THE INVENTION
Accompanied by the increase of the magnetic recording density, the track width must be made narrower. As the track width becomes narrower, the strength of the signal magnetization decreases. The MI head in the prior art has no sufficient sensitivity with respect to such narrow track. Therefore, an MI head having a higher sensitivity is needed. An object of the present invention is to provide an MI head having a higher sensitivity than that in the prior art.
The MI head utilizing the magneto-impedance effect has a high reproduction sensitivity and is suitable for high density recording media. However, since the MI head is exclusively for reproducing, a separate recording head must be used for recording. Another object of the present invention is to provide a recording and reproducing head by adding a recording capability to a reproducing head utilizing the magneto-impedance effect.
A magnetic head of the present invention comprises: a first soft magnetic film formed on a non-magnetic substrate; a second soft magnetic film having a thickness smaller than the thickness of the first soft magnetic film, and formed on the substrate in contact with an end portion of the first soft magnetic film; an electrically conductive metal film formed on the second soft magnetic film; a third soft magnetic film having a thickness smaller than the thickness of the first soft magnetic film, and formed on the electrically conductive metal film so that an end portion of the third soft magnetic film contacts the first soft magnetic film; a magnetic path portion of a soft magnetic film formed on the substrate in contact with an end portion of each of the second and third soft magnetic films, and having a thickness greater than the thickness of each of the second and third soft magnetic films; and a return path yoke formed by facing to the magnetic path portion at one end portion thereof with a non-magnetic gap member interposed therebetween, contacting to the first soft magnetic film at the other end portion, and with a center portion thereof separated from the third soft magnetic film by a non-magnetic portion interposed therebetween.
When a high frequency current is passed through the electrically conductive metal film, the impedance of the electrically conductive metal film placed between the second and third soft magnetic films changes due to the magnetic flux passing through the first and second soft magnetic films by an external magnetic
Fusayasu Hirotsugu
Kuroe Akio
Muramatsu Sayuri
Murata Akio
Akin Gump Strauss Hauer & Feld L.L.P.
Davidson Dan I
Hudspeth David
Matsushita Electric - Industrial Co., Ltd.
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