Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2000-11-21
2003-03-25
Heinz, A. J. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S321000
Reexamination Certificate
active
06538855
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to magneto-resistive thin film magnetic heads, and more particularly to a magneto-resistive thin film magnetic head employing a magneto-resistive element (hereinafter referred to as an MR element) so as to read digital information recorded on a magnetic recording medium as a magnetic field strength signal from the magnetic recording medium.
2. Description of the Related Art
Conventionally, a magneto-resistive thin film magnetic head (hereinafter referred to as an MR head) which employs an MR element and yokes to lead magnetic flux from a magnetic recording medium to the MR element.
FIGS. 1 through 3
each show a conventional yoke-type MR head. In the following description, the left and right sides of the MR head shown in
FIGS. 1 through 3
are defined as front and rear sides of the MR head, respectively. Ag shown therein, the yoke-type MR head includes a nonmagnetic substrate
2
on which a lower yoke
11
, an upper yoke
12
, an MR element
21
, and nonmagnetic insulating layers
31
and
32
are provided. The lower yoke
11
includes a front portion
11
a
, a rear portion
11
b
, and a center portion
11
c
. The upper yoke
12
includes a front portion
12
a
and a rear portion
12
b.
Each of the lower and upper yokes
11
and
12
is formed of a ferromagnetic material, and a gap
22
is formed between the front and rear portions
12
a
and
12
b
of the upper yoke
12
. The upper yoke
12
is separated by the gap
22
into the front and rear portions
12
a
and
12
b.
The MR element
21
is provided below the position where the gap
22
is formed in the upper yoke
12
so as to be magnetically coupled to the front and rear portions
12
a
and
12
b
of the upper yoke
12
. The lower yoke
11
and the rear portion
12
b
of the upper yoke
12
are Joined to be magnetically coupled. A reproducing head gap
15
(minute gap) is formed between the lower yoke
11
and the front portion
12
a
of the upper yoke
12
.
According to this structure, the front portion
12
a
of Me upper yoke
12
, the MR element
21
, the rear portion
12
b
of the upper yoke
12
, and the lower yoke
11
form a magnetic circuit in the yoke-type MR head so that magnetic flux of a signal from a magnetic recording medium such as a magnetic tape, which flux is detected by the reproducing head gap
15
, is converted into au electric signal by the MR element
21
so as to obtain a reproduced output (signal). The nonmagnetic insulating layers
31
and
32
ore formed between the lower and upper yokes
11
and
12
.
FIG. 4
shows the waveform of a reproduced signal which is obtained when a reproduction process is performed, using the yoke-type MR head having the above-mentioned structure, on a magnetic tape
1
on which bits having an equal recording wavelength are recorded (namely a magnetic tape on which recorded is a signal which Is reversed magnetically at a predetermined period).
As described above, the signal, which is reversed magnetically at the predetermined period, is recorded on the magnetic tape
1
. Therefore, if the reproduction process is well performed, a rectangular signal shown by a dot-dash line in
FIG. 4
should be output. However, as shown in
FIG. 4
, the conventional MR head distorts the waveform of the reproduced signal (output).
FIG. 3
is a diagram for illustrating the reason for the generation of the distortion of the waveform of the reproduced signal. As shown therein, a plurality of bits
3
n−1
through
3
n+2
. . . Having the equal recording wavelength are formed on the magnetic tape
1
. Further, magnetic reversal regions
4
n−1
through
4
n+3
. . . are formed on corresponding boundary portions each formed between each adjacent two of the bits
3
n−1
through
3
n+2
. . . A recent trend toward a high-density magnetic recording requires a shorter recording wavelength. As a result, each of the bits
3
n−1
through
3
n+2
. . . is also required to have a shorter length in the running directions (indicated by arrows A
1
and A
2
in
FIG. 3
) of the magnetic tape
1
.
According to
FIG. 3
, the reproducing head gap
15
formed in the MR head opposes the bit
3
n
. Magnetic flux
5
from the magnetic reversal region
4
n
, as indicated by an arrow in
FIG. 3
, forms a magnetic path from the front portion
12
a
of the upper yoke
12
to the magnetic reversal region
4
n+1
by way of the MR element
21
, the rear portion
12
b
of the upper yoke
12
, and the lower yoke
11
.
When the magnetic flux
5
passes through the MR element
21
, the MR element
21
varies an electrical resistance in accordance with a magnetic field applied thereto. Therefore, by causing a sense current to flow through the MR element
21
in advance, a variation in the electrical resistance can be obtained as a value of a voltage drop. The reproduced signal can be thus obtained.
According to
FIG. 3
, if the length of the recording wavelength is equal to or more than the thickness of the front portion
12
a
of the upper yoke
12
, magnetic flux (hereinafter referred to as unnecessary magnetic flux)
6
from the magnetic reversal region
4
, toward the magnetic reversal region
4
n−1
, which is in close proximity to the magnetic reversal region
4
n
, enters the MR element
21
through the front portion
12
a
of the upper yoke
12
.
In other words, since a nonmagnetic coating layer of aluminum oxide (Al
2
O
3
) is provided on the front portion
12
a
of the upper yoke
12
, the unnecessary magnetic flux
6
from the magnetic reversal region
4
, goes to the front portion
12
a
of the upper yoke
12
, which front portion has low magnetic reluctance. Although the direction of the unnecessary magnetic flux
6
is equal to that of the magnetic flux
5
from the proper magnetic reversal regions
4
n
and
4
n+1
, the unnecessary magnetic flux
6
interferes with the magnetic flux
5
, thus causing the distortion of the waveform of the reproduced signal shown in FIG.
4
.
SUMMARY OF THE INVENTION
It IS a general object of the present invention to provide a magneto-resistive thin film magnetic head in which the above disadvantage is eliminated. A more specific object of the present invention is to provide a magneto-resistive thin film magnetic head which is allowed to have an excellent reproduction characteristic by preventing unnecessary magnetic flux from entering a yoke so as to preclude the waveform of a reproduced signal from being distorted.
The above objects of the present invention are achieved by a magneto-resistive thin film magnetic head including: a base; a first yoke provided on the base and separated by a gap into first and second portions, the first portion including a side which opposes a magnetic recording medium; a magneto-resistive element which is magnetically coupled to the first and second portions of the first yoke and detects a magnetic recording signal; a second yoke formed on the first yoke so as to form a reproducing head gap between the first portion of the first yoke and the second yoke; and a third yoke provided between the first portion of the first yoke and the bass so as to be magnetically coupled to the first portion of the first yoke, wherein the reproducing head gap, the first portion of the first yoke, the magneto-resistive element, the second portion of the first yoke, and the second yoke form a circular magnetic circuit.
According to the above-described magneto-resistive thin film magnetic head, the third yoke is provided between the first portion of the first yoke and the base so as to be magnetically coupled to the first portion of the first yoke. Therefore, even if a length of each bit recorded on the magnetic recording medium becomes shorter as a result of a high-density recording, magnetic flux (unnecessary magnetic flux) from a bit in a position separate from a bit opposing the reproducing head gap flows into the third yoke and Is prevented from flowing into the magneto-resistive element via the first yoke because of th
Hasegawa Norio
Hayashi Naoto
Kondo Morio
Machida Kenji
Mutou Kazutoshi
Heinz A. J.
Ladas & Parry
Mitsumi Electric Co. Ltd.
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