Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1999-10-22
2003-10-21
Evans, Jefferson (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06636393
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a magnetic transducer and a thin film magnetic head using the same and more particularly to a magnetic transducer and a thin film magnetic head which can obtain the more excellent rate of resistance change.
2. Description of the Related Art
Recently, an improvement in performance of a thin film magnetic head has been sought in accordance with an improvement in a surface recording density of a hard disk or the like. A composite thin film magnetic head, which has a stacked structure comprising a reproducing head having a magnetoresistive effect (hereinafter referred to as an MR element) that is one of magnetic transducers and a recording head having an inductive-type magnetic transducer, is widely used as the 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, 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, and the GMR head is used as the reproducing head whose surface recording density exceeds 3 gigabits per square inch.
As the GMR film, a “multilayered 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 film is the GMR film which is considered to be relatively simple in structure, to exhibit a great change in resistance even under a low magnetic field and to be suitable for mass production.
FIG. 22
shows the structure of a general spin valve type GMR film (hereinafter referred to as a spin valve film). A surface indicated by reference symbol S in the drawing corresponds to the surface facing a magnetic recording medium. This spin valve film has the stacked structure comprising an underlying layer
91
, a soft magnetic layer
92
made of a soft magnetic material, a nonmagnetic layer
93
made of a nonmagnetic material, a ferromagnetic layer
94
made of a ferromagnetic material, an antiferromagnetic layer
95
made of an antiferromagnetic material and a protective layer
96
, the layers
92
,
93
,
94
,
95
and
96
being stacked in this order on the underlying layer
91
. Exchange coupling occurs on an interface between the ferromagnetic layer
94
and the antiferromagnetic layer
95
, and thus the orientation of magnetization Mp of the ferromagnetic layer
94
is fixed in a fixed direction. On the other hand, the orientation of magnetization Mf of the soft magnetic layer
92
is freely changed in accordance with an external magnetic field.
A direct current is fed through the ferromagnetic layer
94
, the nonmagnetic layer
93
and the soft magnetic layer
92
in the direction of a biasing magnetic field Hb, for example. This current is subjected to the resistance in accordance with a relative angle between the orientation of the magnetization Mf of the soft magnetic layer
92
and the orientation of the magnetization Mp of the ferromagnetic layer
94
. Application of a signal magnetic field causes the change in the orientation of the magnetization Mf of the soft magnetic layer
92
and thus the change in electrical resistance of the spin valve film. The change in the resistance is detected as the change in a voltage. Recently, the greater a rate of resistance change (sometimes referred to as a rate of MR change) has been desired in order to allow magnetic recording at ultra-high density exceeding 20 gigabits per square inch.
A cited reference “CoFe specular spin valves with a nano oxide layer”, 1999 Digests of INTERMAG 99, published by May 18, 1999 reports that the rate of resistance change is improved by providing an oxide layer called an NOL layer for the ferromagnetic layer of the spin valve film.
Moreover, U.S. Pat. No. 5,408,377 discloses the spin valve film having the structure comprising the soft magnetic layer including therein a coupling layer (an AF coupling film) made of ruthenium (Ru) in order to increase the rate of resistance change. Furthermore, U.S. Pat. No. 5,828,529 discloses another spin valve film having the structure comprising the ferromagnetic layer including therein the coupling layer made of ruthenium.
However, there is no description about the material and film thickness of the oxide layer called the NOL layer in the above-described cited reference “CoFe specular spin valves with a nano oxide layer”, 1999 Digests of INTERMAG 99, published on May 18, 1999. Moreover, it is not clear the part of where the NOL layer is formed in the ferromagnetic layer.
Additionally, the improvement in the rate of resistance change is not given specifically and a relationship between the rate of resistance change and any other properties is not clear in U.S. Pat. Nos. 5,408,377 and 5,828,529.
SUMMARY OF THE INVENTION
The invention is made in view of the above problems. It is an object of the invention to provide a magnetic transducer and a thin film magnetic head which can increase a rate of resistance change and can also obtain good values of other properties.
A magnetic transducer of the invention comprises a nonmagnetic layer having a pair of facing surfaces, a soft magnetic layer formed on one surface of the nonmagnetic layer, a ferromagnetic layer formed on the other surface of the nonmagnetic layer and capable of having two magnetizations oriented in opposite directions, and an antiferromagnetic layer formed on the ferromagnetic layer on the side opposite to the nonmagnetic layer, wherein the ferromagnetic layer includes a ferromagnetic interlayer having magnetism and the ferromagnetic interlayer has higher electrical resistance than at least a part of the rest of the ferromagnetic layer.
In the magnetic transducer of the invention, the ferromagnetic layer has two magnetizations oriented in opposite directions, thereby reducing an influence of a magnetic field generated by the ferromagnetic layer upon the soft magnetic layer. Moreover, the electrical resistance of the ferromagnetic interlayer is higher than the electrical resistance of at least a part of the rest of the ferromagnetic layer. Thus, when a sense current flows through the magnetic transducer, the ferromagnetic interlayer reflects at least some electrons and thus limits a route by which the electrons move. As a result, the rate of resistance change is increased and thus even a low signal magnetic field can be detected. Furthermore, since the ferromagnetic interlayer has the magnetism, two portions in the ferromagnetic layer facing each other. across the ferromagnetic interlayer are magnetically integrated with each other.
The magnetic transducer of the invention can further adopt the following modes in addition to the above-described configuration.
In the magnetic transducer of the invention, it is desirable that a distance D
k1
between the nonmagnetic layer and the ferromagnetic interlayer is from 1.5 nm to 3 nm inclusive. Moreover, it is desirable that a thickness of the ferromagnetic interlayer is from 0.5 nm to 1 nm inclusive.
Desirably, the ferromagnetic layer includes an inner ferromagnetic layer, an outer ferromagnetic layer and a coupling layer sandwiched therebetween, and the inner ferromagnetic layer and the outer ferromagnetic layer are magnetically coupled to each other sandwiching the coupling layer. Such a configuration allows the ferromagnetic layer to have two magnetizations oriented in opposite directions. In this case, desirably, a relationship between the distance D
k1
between the nonmagnetic layer and the ferromagnetic interlayer and a distance D
k2
between the ferromagnetic interlayer and the coupling layer of the ferromagnetic layer is defined as 1.2≦D
k1
/D
k2
≦3.
Additionally, the inner ferromagnetic layer may have a first in
Araki Satoru
Sano Masashi
Tsuchiya Yoshihiro
Evans Jefferson
Oliff & Berridge PLC.
TDK Corporation
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