Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2001-08-23
2003-10-14
Ometz, David L. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C428S692100
Reexamination Certificate
active
06633460
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic head employing a magnetoresistive device, and more particularly to a technique for providing a magnetic head that has a reduced amount of change in asymmetry with respect to the MR height, and that exhibits better reproduction characteristics
2. Description of the Related Art
In magnetic heads for use in VCRs, data storage units of computers, etc., the track width has been narrowed in recent years as a result of an increase in recording density and conversion into a digital form of signal recording.
Against such a background, various MIG (Metal In Gap) magnetic heads have hitherto been employed. An MIG magnetic head has a structure with a pair of magnetic core halves, each of which is fabricated by forming, on a core half made of ferrite or ceramic, a metal magnetic thin film having superior soft magnetic characteristics. The core halves are joined to each other by a bonding material, such as a fusing glass, with an insulating film interposed between the magnetic core halves.
Recently, in an attempt to obtain narrower tracks than those possible in MIG magnetic heads, efforts have been made to apply a magnetic head utilizing a magnetoresistive device (MR device) as a device for reproducing magnetic recording information in VCRs, data storage units, etc.
FIG. 13
shows the sectional structure of a principal part of a conventional magnetic head. This magnetic head comprises two half cores, an MR head section for reproduction, and a write head section for recording, both of the head sections being formed between the half cores.
As shown in
FIG. 13
, an MR head section
110
for reproduction is formed on an insulating layer
104
that is formed on an end surface
103
a
of one half core
103
. The MR head section
110
is made up of a lower shield layer
112
and a lower insulating layer
113
, which are successively formed on the insulating layer
104
in that order, a magnetoresistive device (hereinafter referred to as an “MR device”)
120
is formed on the lower insulating layer
113
and is exposed to a medium sliding surface
102
. An upper insulating layer
114
covers the MR device
120
, and an upper shield layer
115
is formed on the upper insulating layer
114
. The upper shield layer
115
also serves as a lower core layer for a write head section
111
described below.
The write head section
111
is made up of a lower core layer (upper shield layer)
115
, a gap layer
116
and a coil
117
, which are successively formed on the lower core layer
115
in that order, an upper insulating layer
118
covering the coil
117
, and an upper core layer
119
joined at one end to the gap layer
116
and at the other end to the lower core layer
115
on the side of the coil
117
.
More specifically, a base end
119
b
of the upper core layer
119
is magnetically coupled to the lower core layer
115
in a substantially central portion of the coil
117
. A core protective layer
130
made of, e.g., alumina, is formed on the upper core layer
119
, and the other half core (not shown) is joined to the core protective layer
130
from above.
The MR device
120
is formed of a thin film of a soft magnetic alloy such as a Ni—Fe alloy, and is connected to an MR electrode
121
. The MR device
120
is also exposed at its part to the medium sliding surface
102
, and has the MR height h of a predetermined dimension in a direction perpendicular to the medium sliding surface
102
(i.e., in a direction of arrow Z shown in FIG.
13
).
As will be described later, the dimension of the MR height h of the MR device
120
gives an important effect upon reproduction characteristics of the MR head section
110
, and therefore the dimensional accuracy of the MR height h must be closely managed. Usually, the MR height h is adjusted by polishing the medium sliding surface
102
.
A Ni—Fe alloy film has hitherto been used in the MR device
120
, and it is known that the magnitude of a reproduction output from the MR head section
110
depends upon the magnetostriction constant of the Ni—Fe alloy film. In a conventional magnetic head, therefore, a Ni—Fe alloy film with the magnetostriction constant having a positive value is used to increase the reproduction output. In order to make positive the magnetostriction constant of the Ni—Fe alloy film, the composition ratio of Fe must not be lower than 19% by weight.
For the above-mentioned reason, most of MR devices used in conventional magnetic heads are formed of Ni—Fe alloys in which the composition ratio of Fe is not lower than 19% by weight.
On the other hand, in the case of employing a digital magnetic recording method, the symmetry in peak heights of a reproduction signal obtained by a magnetic head, i.e., the so-called asymmetry, occurs as a problem to be considered in addition to the magnitude of the reproduction output. The reproduction signal in a digital magnetic recording shows a waveform defined by a series of successive pulse waveforms that are reversed alternately in the positive and negative directions. If the symmetry in peak heights of successive pulse waveforms reversed alternately in the positive and negative directions is deteriorated, read errors may be increased.
Preventing the occurrence of read errors requires a reproduction signal having good symmetry, that is, by reducing the asymmetry of a magnetic head to 0%. The asymmetry of a magnetic head depends upon the MR height h of the MR device
120
.
Although the MR height h is adjusted by polishing the medium sliding surface
102
, the polishing accuracy is about 0.01 &mgr;m at a minimum and hence a variation in asymmetry may sometimes occur.
To suppress the variation in asymmetry, it is therefore necessary that the change in asymmetry be kept as small as possible, even with a change in the MR height h on the order of 0.01 &mgr;m.
Although a conventional magnetic head employing the MR device
120
whose magnetostriction constant has a positive value is superior in the reproduction output, it is disadvantageous in providing a larger amount of change in asymmetry with respect to the MR height h. An improvement in polishing accuracy of the MR height h should be effective in suppressing a variation in asymmetry. In the present state of the art, however, it is difficult to further improve the polishing accuracy of the MR height. Thus, the variation in asymmetry of the magnetic head cannot be suppressed to a satisfactory level.
Additionally, with an increase in magnetic recording density, an increased reproduction rate is demanded, and the use of higher frequencies to produce a recording magnetic field is likewise demanded. Precise reading of a recording magnetic field at higher frequencies requires a magnetic head having a higher resolution. However, the resolution of a conventional magnetic head is not sufficient for satisfying the above demand.
The inventors have made intensive studies with a view to overcoming the problems described above, and have found that there is a specific relationship between the asymmetry of a magnetic head and the magnetostriction constant of an MR device. Based on such a specific relationship, the inventors have accomplished the present invention.
SUMMARY OF THE INVENTION
In view of the state of the art described above, it is an object of the present invention to provide a magnetic head that has a smaller amount of change in asymmetry (i.e., symmetry in peak heights of a reproduction signal) with respect to the MR height, and has an improved resolution for the reproduction signal.
To achieve the above object, the present invention is constituted as follows.
According to one aspect of the present invention, there is provided a magnetic head including a magnetoresistive device as a read device for reading magnetic recording information recorded on a magnetic recording medium while contacting the magnetic recording medium, wherein a magnetostriction constant of a soft magnetic substance forming the magnetoresistive device is 0 or below.
With the magnetic head havin
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Ometz David L.
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