Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2000-06-23
2003-04-08
Evans, Jefferson (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S324100
Reexamination Certificate
active
06545848
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic transducer such as a magnetoresistive element, a thin film magnetic head and a method of manufacturing the same. More particularly, the present invention relates to a magnetic transducer comprising a magnetic domain control film to suppress, for example, Barkhausen noise or the like, a thin film magnetic head and a method of manufacturing the same.
2. Description of the Related Art
Recently, an improvement in performance of a thin film magnetic head has been sought in accordance with an increase in a surface recording density of a hard disk drive. A composite thin film magnetic head, which has a stacked structure comprising a reproducing head having a magnetoresistive element (hereinafter also referred to as an MR element) and a recording head having an inductive-type magnetic transducer, is widely used as a thin film magnetic head.
MR elements include an AMR element using a magnetic film (an AMR film) exhibiting an anisotropic magnetoresistive effect (an AMR effect), a GMR element using a magnetic film (a GMR film) exhibiting a giant magnetoresistive effect (a GMR effect), and so on.
The reproducing head using the AMR element is called an AMR head or simply an MR head, and the reproducing head using the GMR element is called a GMR head. The AMR head is used as the reproducing head whose surface recording density exceeds 1 gigabit per square inch (0.155 gigabits per square centimeters), and the GMR head is used as the reproducing head whose surface recording density exceeds 3 gigabits per square inch (0.465 gigabits per square centimeters).
As the GMR film, a “multi-layered type (antiferromagnetic type)” film, an “inductive ferromagnetic type” film, a “granular type” film, a “spin valve type” film and the like are proposed. Of these types of films, the spin valve type GMR film is most efficient as the GMR film which is relatively simple in structure, exhibits a great change in resistance in a low magnetic field, and is suitable for mass-production.
FIG. 20
is a sectional view of the magnetoresistive element, which uses a spin valve type GMR film (hereinafter referred to as a spin valve film) disclosed in Unexamined Patent Application Publication No. Hei 8-45032, parallel to the opposed face (medium-facing surface or air bearing surface; ABS) to a magnetic recording medium. The magnetoresistive element has the stacked structure comprising a free layer
63
made of a soft magnetic material, a spacer layer
65
made of a nonmagnetic metal, a pinned layer
70
made of a ferromagnetic material and an antiferromagnetic layer
66
made of an antiferromagnetic material in the order named on an underlayer
62
made of Ta (tantalum) or the like. The antiferromagnetic layer
66
is covered with a protective layer
67
. Exchange coupling is induced on an interface between the pinned layer
70
and the antiferromagnetic layer
66
, and thus the orientation of the magnetization of the pinned layer
70
is fixed in a direction indicated by
71
in the drawing, for instance. On the other hand, the orientation of the magnetization of the free layer
63
is freely changed in accordance with a signal magnetic field from a magnetic recording medium because the free layer
63
is isolated from the antiferromagnetic layer
66
by the spacer layer
65
.
Reproducing of information using such a spin valve film, that is, the detection of a signal magnetic field from a magnetic recording medium is performed as follows. A detecting current (sense current) as a direct constant current is fed through the free layer
63
through lead electrode layers
92
a
and
92
b
in the direction indicated by
64
in the drawing, for example. Receiving the signal magnetic field from the magnetic recording medium rotates the magnetization of the free layer
63
. The current passing through the free layer
63
is subjected to the resistance in accordance with a relative angle between the orientation of the magnetization of the free layer
63
and the fixed orientation of the magnetization of the pinned layer
70
and thus the resistance is detected as a voltage.
In such a magnetoresistive element, it is considered to apply a bias magnetic field to the free layer
63
to reduce Barkhausen noise. The Barkhausen noise is caused when many magnetic domains having random orientations of magnetizations change to one large magnetic domain, that is, change to a single magnetic domain, having a common orientation of magnetization under the influence of an external magnetic field.
Providing a magnetic domain control film produces the bias magnetic field. The magnetic domain control film is consisted of two layers of magnetic domain control ferromagnetic films
90
a
and
90
b
formed to sandwich the free layer
63
and of magnetic domain control antiferromagnetic films
90
a
and
90
b
deposited thereon, respectively. The orientation of the magnetizations of the domain control ferromagnetic films
90
a
and
90
b
is fixed by exchange coupling on each interface between the magnetic domain control ferromagnetic film
90
a
and the magnetic domain control antiferromagnetic film
90
a
, and the magnetic domain control ferromagnetic film
90
b
and the magnetic domain control antiferromagnetic film
90
b
in the direction indicated by
90
c
in the drawing. The bias magnetic field indicated by
64
in the drawing is applied to the free layer
63
sandwiched between the magnetic domain control ferromagnetic films
90
a
and
90
b
. The bias magnetic field flows to the same direction as sense current and is called as a “longitudinal bias”.
The explanation of magnetostriction of the magnetic domain control ferromagnetic films
90
a
and
90
b
will be made here.
FIG. 21
simply illustrates the orientation of the magnetizations of the magnetic domain control ferromagnetic films
90
a
and
90
b
and a bias magnetic field applied to the free layer
63
as seen from above of the magnetoresistive element (the direction indicated by the arrow XXI in FIG.
20
). The face indicated by reference character S in the drawing is a medium-facing surface opposite to the magnetic recording medium.
The magnetoresistive element is overlaid on the shield layer (not shown) or the like to make the reproducing head. It is known that the tensile stress F is applied on such reproducing head in the direction orthogonal to the medium-facing surface S. At this time, “tensile strain” (strain in the direction of the expansion Exp) parallel to the tensile stress F and “compression strain” (strain in the direction of the compression Com) perpendicular to the tensile stress F are developed in the magnetic transducer. If the magnetostrictios &lgr;s of the magnetic domain control ferromagnetic films
90
a
and
90
b
is positive, the magnetization thereof may orient the same direction as tensile strain. That is, the magnetization of the magnetic domain control ferromagnetic films
90
a
and
90
b
rotates toward the tensile direction as indicated by dashed lines in the drawing. In this case, the bias magnetic field produced in the free layer
63
is weakened by the rotation of the magnetic domain control ferromagnetic films
90
a
and
90
b.
Unexamined Patent Application Publication No. Hei 6-84145 proposes that the magnetostriction &lgr;s of the magnetic domain control ferromagnetic film is a negative value having a large absolute value, specifically, &lgr;s≦−15×10
−6
. If the magnetostriction &lgr;s of the magnetic domain control ferromagnetic film is negative, when the tensile stress F is applied to the magnetic domain control ferromagnetic films
90
a
and
90
b
as in
FIG. 21
, the magnetization thereof may orient to the direction of compression strain. In this case, the magnetic domain control ferromagnetic films
90
a
and
90
b
do not rotate and therefore the bias magnetic field produced in the free layer
63
is not weakened.
However, if the magnetostriction &lgr;s of the magnetic domain control ferromagnetic film is set to &lgr;s≦&min
Evans Jefferson
TDK Corporation
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