Dynamic magnetic information storage or retrieval – Head – Core
Reexamination Certificate
2000-06-27
2003-03-25
Evans, Jefferson (Department: 2754)
Dynamic magnetic information storage or retrieval
Head
Core
Reexamination Certificate
active
06538845
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to thin-film magnetic heads which are mounted in, for example, hard disk drives. In particular, the present invention relates to thin-film magnetic heads suitable for higher recording densities and higher recording frequencies and relates to methods for making the same.
2. Description of the Related Art
FIG. 9
is an enlarged cross-sectional view of a conventional thin-film magnetic head. This thin-film magnetic head is an inductive head for writing. A MR head for reading may be formed below the inductive head. The thin-film magnetic head has a lower core layer
1
formed of a conventional magnetic material such as permalloy. A gap layer
2
of alumina or the like is formed on the lower core layer
1
, and an insulating layer
3
composed of polyimide or a resist material is formed on the gap layer
2
.
A coil layer
4
having a spiral pattern is formed on the insulating layer
3
. The coil layer
4
is formed of a nonmagnetic conductive material having low electrical resistance, such as copper. The coil layer
4
is covered with an insulating layer
5
formed of polyimide or a resist material. An upper core layer
6
formed of a magnetic material such as permalloy is plated on the insulating layer
5
.
The upper core layer
6
faces the lower core layer
1
at a surface opposing a recording medium (air bearing surface (ABS)) and these layers are separated by the gap layer
2
. The gap layer
2
forms a magnetic gap with a magnetic gap length GL
1
which applies a recording magnetic field to a recording medium. A base end
6
b
of the upper core layer
6
is magnetically coupled with the lower core layer
1
.
In this inductive head, the coil layer
4
yields a recording magnetic field by a recording current flowing therein toward the upper core layer
6
and the lower core layer
1
. A magnetic signal is recorded on a recording medium, such as a hard disk, by a fringing magnetic field between the lower core layer
1
and the upper core layer
6
at the magnetic gap.
With trends toward higher recording densities and higher recording frequencies, the saturation magnetic flux density B
s
and the specific resistance &rgr; of the upper core layer
6
must be increased. The specific resistance &rgr; is an important magnetic characteristic in order to reduce eddy current loss at high-frequencies. However, NiFe alloys, which are generally used in the upper core layer
6
, have at most 50 &mgr;&OHgr;·cm. As a result, in conventional thin-film magnetic heads, eddy current loss is insufficiently suppressed at high-frequencies.
The high saturation magnetic flux density B
s
is a magnetic characteristic which is essential for improved recording density. When the upper core layer
6
is formed of a magnetic material having high saturation magnetic flux density B
s
which is suitable for higher recording densities and higher recording frequencies, the specific resistance &rgr; is further decreased and thus the eddy current loss is unintentionally increased. When the upper core layer
6
is formed of a magnetic material having high specific resistance &rgr;, the saturation magnetic flux density B
s
will be be sacrificed to some extent.
The following conventional thin-film magnetic head provides an improved saturation magnetic flux density B
s
. In this head, the upper core layer
6
shown in
FIG. 9
has two films, that is, a high B
s
film having high saturation magnetic flux density B
s
and a conventional permalloy film (a NiFe alloy film) in order to be suitable for high recording densities. The lower core layer
1
is composed of only a permalloy film.
Since a recording magnetic field is generated from a portion which is near the gap layer
2
of a leading edge
6
a
of the upper core layer
6
toward the lower core layer
1
, the high B
s
film is believed to intensively generate the magnetic field near the gap and this is suitable for future higher recording densities.
This double-layer structure can improve recording characteristics compared to the above single upper core layer
6
composed of permalloy. However, a recording magnetic field formed between the high B
s
film and the lower core layer
1
is affected by a magnetic field from the recording medium, and an intensive recording magnetic field will not be concentrated near the gap. As a result, this structure cannot effectively improve an overwrite (OW) characteristic and a non-linear transition shift (NLTS) characteristic, as described in detail below.
The NLTS exhibits a phase lead by nonlinear distortion of a magnetic field generated at the magnetic gap between the upper and lower core layers
1
and
6
, respectively, which is caused by a recorded magnetic field from magnetic signals recorded immediately before on the recording medium toward the head.
In order to evaluate the OW characteristic, low-frequency signals are recorded and then high-frequency signals are overwritten. The OW characteristic is evaluated by a decrease in residual output of the low-frequency recorded signals after the high-frequency overwriting compared to the recorded signals after low-frequency recording.
Moreover, this double layer structure does not effectively reduce eddy current loss which is caused by increased recording frequencies.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a thin-film magnetic head including an upper core layer and a lower core layer which have improved structures and which comprise improved magnetic materials.
It is another object of the present invention to provide a thin-film magnetic head which is suitable for higher recording densities and higher recording frequencies.
It is another object of the present invention to provide a method for making a thin-film magnetic head.
According to a first aspect of the present invention, a thin-film magnetic head includes a gap layer; a magnetic pole layer optionally provided on one face of the gap layer; a lower core layer; an upper core layer, the lower core layer and the upper core layer facing each other and being separated by the gap layer; and a coil layer for applying a recording magnetic field to the lower core layer and the upper core layer. At least one of the lower core layer and the upper core layer includes a soft magnetic layer and at least one high-specific-resistance layer formed on at least one of the upper face and the lower face of the soft magnetic layer, and the high-specific-resistance layer has a specific resistance which is higher than the specific resistance of the soft magnetic layer.
In the present invention, at least one of the lower core layer and the upper core layer includes the soft magnetic layer and at least one high-specific-resistance layer formed on at least one of the upper face and the lower face of the soft magnetic layer. This structure can reduce eddy current loss which is generated by increased recording frequencies. Thus, this thin-film magnetic head is suitable for future higher recording frequencies.
In the present invention, the high-specific-resistance layer is formed on the core layer, because eddy current loss is particularly generated in the vicinity of the core layer by skin effects.
Preferably, the high-specific-resistance layer is formed on the upper face of the upper core layer and is covered with a protective film. The protective film can prevent cracks of the high-specific-resistance layer which is generally formed of a fragile material.
Preferably, the protective film is formed of one of a NiFe alloy, elemental Ni, and a NiP alloy.
Preferably, the high-specific-resistance layer is formed at a portion other than a magnetic path-forming region toward the gap layer on at least one of the lower face of the upper core layer and the upper face of the lower core layer.
If the high-specific-resistance layer is formed in the magnetic path-forming region, a recording magnetic field generated in the vicinity of the gap is reduced. When the high-specific-resistance layer is formed on the upper face of the upper core lay
Kawasaki Mitsuo
Watanabe Toshinori
LandOfFree
Thin-film magnetic head having a high specific resistance layer does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Thin-film magnetic head having a high specific resistance layer, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Thin-film magnetic head having a high specific resistance layer will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3035148