Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1999-07-07
2002-02-05
Letscher, George J. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06344955
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetoresistive element using a magnetoresistance effect and a thin film magnetic head comprising the magnetoresistive element.
2. Related Art Statement
Under a tendency of miniaturization of a magnetic disk drive unit, a thin film magnetic head using a magnetoresistive element (hereinafter, referred to as an MR element also) as a read head is known as a magnetic/electric converter suitable for reading information stored in a high recording density on a magnetic medium since its output is not related to the relative speed of the head to a magnetic disk.
As an MR element used in such a thin film magnetic head, an MR element using an anisotropic magnetoresistance effect film (hereinafter, referred to as an AMR film) made of permalloy and the like, and a gigantic magnetoresistive element (hereinafter, referred to as a GMR element) using a spin valve film structure (hereinafter, referred to as an SV film structure) are known. These MR elements each contain a magnetic sensitive film responding to a magnetic field applied from the outside. In case of an AMR element an AMR film corresponds to the magnetic sensitive film, and in case of a GMR element of a spin valve structure a free layer corresponds to the magnetic sensitive film. A longitudinal bias magnetic field (a single domain anisotropic magnetic field) is applied to the magnetic sensitive film by a magnetic domain control film. This longitudinal bias magnetic field makes the magnetic sensitive film into a single magnetic domain and suppresses a Barkhausen noise to be caused by movement of a domain wall. As a method for applying a longitudinal bias magnetic field, an exchange bias method utilizing the exchange coupling between an antiferromagnetic film and a magnetic film, and a hard magnetic bias method using a hard magnetic film are known.
For example, an exchange bias method is disclosed in Japanese Patent Laid-Open Publication No. Sho 62-40,610 and U.S. Pat. No. 4,103,315. The respective magnetic domain control films in an MR element disclosed in these prior technical documents are stacked with a space between them on both sides being opposite to each other of an AMR film to be a magnetic sensitive film. A magnetic domain control film comprises an antiferromagnetic film. And utilizing an exchange coupling generated between an antiferromagnetic film and a magnetic film, this method applies a uniform longitudinal bias magnetic field to the AMR film to make it into a single magnetic domain and thereby prevents a Barkhausen noise to be caused by movement of a magnetic domain.
The specification of U.S. Pat. No. 5,528,440 discloses an exchange bias method which makes a magnetic domain control film have a film structure generating an exchange coupling by forming an antiferromagnetic film of an NiMn layer on an NiFe layer and brings an end portion of this magnetic domain control film into contact with an AMR film.
Japanese Patent Laid-Open Publication No. Hei 7-244,821 discloses a technique which removes an antioxidizing film on the surface of an AMR element layer by cutting by a specified amount both end portions in the longitudinal direction of the AMR element, forms an antiferromagnetic film in an area where an exchange coupling can be generated, generates an exchange coupling between a magnetic film and the antiferromagnetic film, and applies a longitudinal bias magnetic field.
Japanese Patent Laid-Open Publication No. Hei 7-210,834 discloses a film structure having magnetic domain control films provided on both ends in the longitudinal direction of an AMR film, wherein a buffer layer composed of an NiFe film is provided between the AMR film and the magnetic domain control film.
Further, a hard magnetic bias method has been disclosed in Japanese Patent Laid-Open Publication No. Hei 3-125,311. In this prior technical document, hard magnetic films are formed in end passive areas at both sides of it.
A GMR element having an SV film structure is disclosed in Japanese Patent Laid-Open Publication No. Hei 4-358,310 and IEEE TRANSACTIONS ON MAGNETICS, Vol. 30, No. 6, NOVEMBER 1994, pp. 3801-3806. This known SV film structure has basically a structure having a pin layer and a free layer stacked with a nonmagnetic layer between them. The pin layer has the direction of magnetization fixed in one direction, and the free layer has the direction of magnetization freely moving in response to a magnetic field applied from the outside. The SV film structure has the minimum resistance value when the pin layer and the free layer have the same direction of magnetization, and has the maximum resistance value when they are inverse to each other in direction of magnetization. An external magnetic field is detected by utilizing this resistance change characteristic.
In the SV film structure also, a magnetic domain control film for applying a longitudinal bias magnetic field to a free layer is provided. As a magnetic domain control film, a film structure by an exchange bias method and a film structure by a hard magnetic bias method are known.
Although a longitudinal bias magnetic field by a magnetic domain control film is necessary for making a magnetic sensitive film into a single magnetic domain, a too large longitudinal bias magnetic field degrades the reproduction sensitivity of the magnetic sensitive film. Accordingly, the intensity of a longitudinal bias magnetic field needs to be set so as to make a magnetic sensitive film into a single magnetic domain but so as not to degrade the reproduction sensitivity of the magnetic sensitive film. The intensity of a longitudinal bias magnetic field varies according to the relation between the thickness and magnetic characteristics of a magnetic sensitive film and the thickness and magnetic characteristics of a magnetic domain control film. In order to set a proper longitudinal bias magnetic field, therefore, it is necessary to clarify an influence which the thickness and magnetic characteristics of a magnetic sensitive film and the thickness and magnetic characteristics of a magnetic domain control film have upon the longitudinal bias magnetic field.
However, the above-mentioned prior technical documents have disclosed methods for applying a longitudinal bias magnetic field to a magnetic sensitive film and thereby making it into a single magnetic domain, but they do not teach at most the relation between the thickness and magnetic characteristics of a magnetic sensitive film and the thickness and magnetic characteristics of a magnetic domain control film, said relation having an influence upon the longitudinal bias magnetic field.
And in order to cope with high-density integration of an MR element, it is necessary to make thinner the thickness of a magnetic sensitive film. For example, in case of an AMR element, it is required to reduce the thickness of a magnetic sensitive film from a thickness of 20 to 25 nm at present to a thickness of 10 nm or less. The above-mentioned prior technical documents do not teach how to determine the thickness of a magnetic domain control film in case that the magnetic sensitive film is made thin as described above.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a magnetoresistive element capable of applying a proper longitudinal bias magnetic field to a magnetic sensitive film according to a change in thickness of the magnetic sensitive film, and a thin film magnetic head provided with the same magnetoresistive element.
Another object of the present invention is to provide a magnetoresistive element capable of applying a proper longitudinal bias magnetic field to a magnetic sensitive film by clarifying an influence which the magnetical thickness of a magnetic sensitive film and the magnetical thickness of a magnetic domain control film have upon the longitudinal bias magnetic field, and a thin film magnetic head provided with the same magnetoresistive element.
A further other object of the present invention is to provide a magnetoresistive element capable o
Hiromatsu Fumihiro
Sato Jun-ichi
Letscher George J.
Oliff & Berridg,e PLC
TDK Corporation
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