Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reissue Patent
2000-01-18
2002-08-13
Heinz, A. J. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reissue Patent
active
RE037819
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
In general, the present invention relates to a magnetic read head utilizing a magnetoresistive effect such as an AMR head or a spin-valve head. In particular, the present invention relates to a magnetoresistive head which sustains the linear response characteristic of the magnetoresistive effect, reduces the amount of Barkhausen noise, lessens the effect of problems encountered in the conventional antiferromagnetic film and effectively applies a bias generated by an exchange coupling magnetic field.
2. Description of the Related Art
Magnetic read heads utilizing a magnetoresistive effect of the conventional technology include an AMR (Anisotropic Magnetoresistance) head based on anisotropic magnetoresistive phenomena and a GMR (Giant Magnetoresistance) head based on spin scattering phenomena of conduction electrons. An example of the GMR head disclosed in U.S. Pat. No. 5,159,513 is a spin-valve head exhibiting a high magnetoresistive effect caused by a weak external magnetic field.
FIGS. 9 through 11
are diagrams showing a skeleton configuration of elements composing the AMR head according to the conventional technology. Reference numeral
1
shown in the figures is a soft magnetic film and reference numeral
2
is a nonmagnetic film. Reference numerals
3
and
4
are a magnetoresistive film and an antiferromagnetic film made of an FeMn alloy respectively. Reference numeral
5
is a ferromagnetic film whereas reference numeral
7
denotes a permanent magnetic film (a hard film). Reference numeral
8
is an antiferromagnetic film.
In order to operate a magnetoresistive head, two bias magnetic fields are required for the magnetoresistive film
3
which exhibits a magnetoresistive effect. One of the bias magnetic fields is used to make changes in resistance in the magnetoresistive film respond linearly to a magnetic flux from a magnetic recording medium. This bias magnetic field is applied in a Z direction perpendicular to the surface of the magnetic recording medium as shown in the figures and is called a lateral bias.
Normally called a longitudinal bias, the other bias magnetic field is applied in an X direction parallel to the surface of the magnetic recording medium and the magnetoresistive film
3
. The longitudinal bias magnetic field is used for reducing the amount of Barkhausen noise which is generated by formation of a plurality of magnetic domains by the magnetoresistive film
3
. In other word, the longitudinal bias magnetic field makes the change in resistance with the magnetic flux from the magnetic recording medium smooth. It is necessary to put the magnetoresistive film
3
in a single-domain state in order to reduce the amount of Barkhausen noise. There are two methods for applying the longitudinal bias for that purpose. According to one of the methods, the permanent magnetic films
7
are located at both the sides of the magnetoresistive film
3
and a leaking magnetic flux from the permanent magnetic films
7
is utilized as is shown in a structure of FIG.
10
. According to the other method, on the other hand, an exchange coupling magnetic field developed on each of the contact boundary surfaces of the magnetoresistive film
3
and the antiferromagnetic films
8
is utilized as is shown in a structure of FIG.
11
.
It is obvious from the structure shown in
FIG. 11
wherein a bias magnetic field is generated from an exchange coupling magnetic field that this method is characterized in that the magnetoresistive film
3
is also created and extended at both ends beyond the region of the read track of the magnetic recording medium. The antiferromagnetic films
8
are created, coming in direct contact with the extended portions of the magnetoresistive film
3
to generate an exchange coupling magnetic field on each of the contact boundary surfaces between the magnetoresistive film
3
and the antiferromagnetic films
8
. By pinning the direction of magnetization in the regions at both the ends of the magnetoresistive film
3
in the read-track direction (that is, the X direction shown in the figure), a bias for putting the magnetization of the read-track region of the magnetoresistive film
3
into a single-domain state in the X direction can be obtained.
The structure shown in
FIG. 11
has the following problems. One of the problems is that, in spite of the fact that the magnetization in the magnetoresistive film
3
in each of the regions outside the read track is pinned in the X direction by the exchange coupling with the antiferromagnetic film
8
, the direction of the magnetization in the magnetoresistive film
3
in the region outside the read track is changed by a magnetic flux from the magnetic recording medium in the Z direction shown in the figure because, normally, the intensity of the exchange coupling magnetic field is of the order in a range of several tens to 200 Oe. As a result, a magnetoresistive effect is observed also in each of the regions at both the ends in which region a magnetoresistive effect should never be observed. This problem gives rise to an inconvenience that the read track width can not be determined.
The other problem is that, since portions the magnetoresistive film in the regions at both the ends outside the read track are contiguous with the portions of the magnetoresistive film inside the read track, noise and irreversibility of the change in magnetization in the magnetoresistive film in the regions at both the ends outside the read track directly affect the change in magnetization of the magnetoresistive film inside the read track, giving rise to generation of Barkhausen noise and irreversibility of the change in magnetization in the magnetoresistive film inside the read track.
It is obvious from the structure shown in
FIG. 10
wherein a bias magnetic field is generated by the permanent magnetic film that the permanent magnetic films
7
are located at both ends of the read-track region and that the direction of magnetization of each of the permanent magnetic films
7
is pinned in the read-track direction (that is, the X direction shown in the figure) by magnetic polarization. By applying a magnetic flux leaking from the permanent magnetic film
7
in the X direction into the magnetoresistive film
3
, a bias for putting the magnetization of the magnetoresistive film
3
in a single-domain state in the read-track direction can be obtained.
The portions of the soft magnetic film
1
, the nonmagnetic film
2
and the magnetoresistive film
3
at both the ends of the read track, which portions are in contact with the permanent magnetic films
7
, must each be formed into a taper shape in order to stabilize the contact resistance against a current for detecting a magnetic resistance flowing from the permanent magnetic film
7
at one end to the soft magnetic film
1
, then to the nonmagnetic film
2
, then to the magnetoresistive film
3
and finally to the permanent magnetic film
7
at the other end. However, the taper shape gives rise to the following problems in the magnetic characteristics of the permanent magnetic film
7
.
One of the problems is that the soft magnetic film
1
, the nonmagnetic film
2
and the magnetoresistive film
3
each become an underlayer in the process of manufacturing the permanent magnetic film
7
at the tapered sections. In general, the magnetic characteristics of a permanent magnetic layer are affected very easily by the underlayer thereof. In the case of the structure shown in
FIG. 10
, the magnetic characteristics of the permanent magnetic film
7
in close proximity to the boundary surface facing the soft magnetic film
1
, the nonmagnetic film
2
and the magnetoresistive film
3
are affected by the three underlayers of different types. As a result, it is extremely difficult to obtain stable magnetic characteristics.
The other problem is that, in order to put the magnetization of the magnetoresistive film
3
in a single-domain state in the read-track direction (that is, in the X direction shown in the figure), the permanent magnet
Kuriyama Toshihiro
Saito Masamichi
Watanabe Toshinori
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Heinz A. J.
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