Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2002-01-10
2004-02-24
Ometz, David L. (Department: 2653)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06697235
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to magnetic recording/reproducing head with magnetoresistive head, and particularly to the structure of the magnetic domain control film of a magnetoresistive head and to the technology for magnetic domain control by GMR film.
In recent years, as the magnetic recording/reproducing apparatus has achieved high-density recording capability, GMR heads for reproducing heads have been practically used which employ spin valve films having magnetoresistive effect as sensor films and permanent magnet layer abutted junction for magnetic domain control, thus making the reproducing track width narrower.
FIG. 9
shows the structure of a conventional magnetic head of the abutted junction type. This structure has a GMR sensor film
1
, a permanent magnet layer
2
and an electrode film
4
intervened between two magnetic shields S
1
and S
2
. The permanent magnetic layer
2
is abutted to both the edges of the GMR sensor film
1
, and the electrode film
4
is formed immediately above the layer
2
. The electrode film
4
and the permanent magnetic layer
2
(which also has conductivity) serve as electrodes for causing current to flow in the GMR film. The permanent magnetic layer
2
also plays a role for domain control to apply a magnetic field to a free layer
8
that constitutes the GMR film
1
, thereby making the orientation of domains in a uniform direction.
Since the strength of the magnetic field from the permanent magnet layer
2
increases with the decrease of the distance to the magnet layer
2
(see
FIG. 3
that shows the distribution of the field strength when the position on the free layer is changed in the track width direction), the magnetization rotation of the free layer in a small region of the GMR film near the permanent magnet layer is restricted by the field from the permanent magnet layer (the orientation of the magnetic domains is strongly fixed by the intense field strength), thus giving rise to a region in which the sensor sensitivity is low (the orientation of magnetic domains becomes difficult to change under the magnetic field from a magnetized recording medium, thus the sensitivity of magnetic head being reduced). This region will be hereinafter referred to as “low-sensitivity region”.
Although a sensitivity distribution of the sensor is shown on the bottom of
FIG. 9
, both the skirts of the peak of the sensitivity distribution correspond to the “low-sensitivity region” as indicated by reference numeral
6
. The low-sensitivity region is located over about 0.05~0.1 &mgr;m from the edges of the permanent magnet. When the reproducing track width is as large as, for example, 1 &mgr;m, the proportion of the low-sensitivity region to the reproducing track width is about 0.2 and thus it is not so significant. However, if the reproducing track width is too narrow, the proportion of the low-sensitivity region to the reproducing track width increases, so that the reproduction output suddenly decreases.
FIG. 10
shows the dependence of the reproduction output on the reproducing track width (dimensional, geometric track width) under a constant MR height (that is a depth from the medium as indicated by a line with arrow heads at both ends in
FIG. 9
) and a constant sense current. From
FIG. 10
it will be understood that the reproduction output more suddenly decreases than the proportional relation indicated by the dotted line, and becomes zero at an effective track width of 0.15 &mgr;m when extrapolated.
The recording density of 70 G bits/in
2
or above needs a reproducing track width (magnetic track width) of 0.2 &mgr;m or below. Since a reproduction output of about 1 mV is necessary in order to normally operate the hard disk drive, the reproduction output of the conventional permanent magnet abutted junction type GMR head is too low, and thus the information written on the recording medium cannot be reproduced.
In order to prevent the reproduction output from being drastically reduced due to this narrow track width, an electrode overlap type GMR head is proposed as in JP-A-11-53716.
FIG. 11
shows the structure of the electrode overlap type GMR head. This structure has a pair of permanent magnet layers
2
abutted to both the edges of the GMR sensor film
1
that is formed to have a desired width, and a pair of electrode films
4
formed on the permanent magnet layers
2
and overlapped on part of the GMR film
1
. Thus, the distance DLD between the pair of electrodes
4
is smaller than the distance DCD between the pair of permanent magnet layers
2
serving as magnetic domain control films.
Since current is caused to flow chiefly in the DLD region of GMR film
1
between the pair of electrodes in the structure shown in
FIG. 11
, the sensitivity region of the sensor film is the DLD region. Since the permanent magnet layers are sufficiently separated from this region, the sensitivity of the DLD region is expected not to decrease. In other words, the electrode film edges are located out of the low-sensitivity region that is produced by the high field strength near the permanent magnet layers.
However, after detailed examination of the sensor sensitivity distribution, it has been revealed that, as shown in
FIG. 11
, the sensitivity distribution of the sensor film is wider than the region DLD between the electrodes, resulting in the fact that the reproducing track width is larger than the electrode distance DLD. Therefore, it was found that in order to obtain a desired reproducing track width, the electrode film distance DLD must be decreased to be smaller than the desired width.
The reason for the reproducing track width to be larger than the DLD is that the magnetic flux from the medium into the free layer
8
just under the electrodes propagates up to the free layer of DLD region, changing the resistance of the GMR sensor film. In other words, the magnetic flux flowing from the medium into the free layer right under part of the electrode films
4
that is directly overlapped on the free layer as shown in
FIG. 11
affects the DLD region of the sensor film to change the resistance of the GMR sensor film between the electrodes, so that the voltage between the electrodes is changed.
One method for solving the above problem is to reduce the electrode film distance DLD that is expected to be smaller than the reproducing track width. This method, however, requires the photolithography for further narrow distance DLD, and thus has a difficulty in the production process.
Another means for improving the sensitivity of the sensor is to reduce the magnetic domain control force by the permanent magnet layers, or to properly weaken the magnetic field strength in the free layer in which the field strength at the edges of the sensor film shown in
FIG. 3
is too strong as described later. However, the domain control is not satisfactorily made (the domains are not uniformly magnetized) due to the irregularity of the amount that the electrodes and domain control films are overlapped at the edges of the sensor film and the irregularity of the angles, thus causing the waveform to vary.
The prior art permanent magnet layer abutted junction type head thus has the problem that the output is drastically reduced due to the reduction of the reproducing track width as described above.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a reproduce head with the above problems solved, with high reproduction sensitivity and with narrow reproduction track width without waveform variation.
The present invention employs chiefly the following construction in order to solve the above problems.
A magnetoresistive head having a substrate, first and second magnetic shields formed on the top of the substrate, a magnetoresistive effect film formed within a gap layer between the first and second magnetic shields, a permanent magnet layer formed on both sides of the magnetoresistive effect film to apply a magnetic field thereto, and an electrode film formed on the permanent magnet layer to permit a signal detected cu
Nishioka Koichi
Ohtsu Takayoshi
Hitachi , Ltd.
Ometz David L.
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