Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1999-06-30
2001-11-06
Heinz, A. J. (Department: 2165)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06313973
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a magnetoresistive element having an change coupling film utilizing an exchanging coupling between an antiferromagnetic film and a ferromagnetic film, a magnetic head using the magnetoresistive element, and a magnetic disk drive using the magnetic head.
2. Description of the Background
As a read head in a high density magnetic recording, a magnetic head using a magnetoresistive element has been studied. At present, an 80 at % Ni-20 at % Fe (coummn name: permalloy) alloy thin-film is used as a material of the magnetoresistive element. In recent years, as materials substituted for this, artificial lattice films and spin valve films, such as (Co/Cu)n, which have a giant magnetoresistance effect, are widely noticed.
Since the magnetoresistance effect film of permalloy has magnetic domains, the Barkhausen noises resulting from this are much of a problem for practical use. Therefore, various methods for causing a magnetoresistance efts film to have a single magnetic domain are studied. As one of the methods, there is used a method for controlling the magnetic domains of a magnetoresistance effect film in a specific direction using an exchanging coupling between a magnetoresistance effect film, which is a ferromagnetic film, and an antiferromagnetic film. As the antiferromagnetic material, &ggr;-FeMn alloy is well known (e.g., U.S. Pat. No. 4,103,315 and U.S. Pat. No. 5,015,147). This magnetoresistance effect is called anisotropic magnetoresistance effect.
Moreover, in recent years, the art utilizing an exchanging coupling between an antiferromagnetic film and a ferromagnetic film is widely used in order to pin the magnetization of a magnetic film of a spin valve film. Also for this purpose, &ggr;-FeMn alloy is widely used as the antiferromagnetic film.
However, the &ggr;-FeMn alloy has the problem of corrosion resistance, particularly corrosion due to water, so that there is a problem in that the exchange coupling field to a magnetoresistance effect film as a magnetoresistive element is deteriorated by corrosion at a processing step or corrosion due to water in atmosphere as time elapses.
In addition, the pentium processor recently incorporated in a machine having an accelerated throughput has a very large heating value, so that the temperature in an HDD also rises to about 150° C. during operation. Therefore, an exchange coupling field of 200 Oe or more at 150° C. is required in view of reliability. In order to obtain an exchange coupling field of 200 Oe or more at 150° C., it is desired that the exchange coupling field at room temperature is not only high, but the temperature characteristic of the exchange coupling field is also good. Moreover, it is required that the blocking temperature, at which the exchanging coupling between the ferromagnetic film and the antiferromagnetic film disappears, should be as higher as possible.
However, the blocking temperature of the &ggr;-FeMn alloy is 170° C. or lower. In addition, the temperature characteristic of the exchange coupling field is very bad. Therefore, the exchange coupling field is not sufficient at 100° C., so that there is a problem in that there is no long-term reliability.
In addition, U.S. Pat. No. 4,103,315 discloses the use of oxides, such as NiO. Moreover, U.S. Pat. No. 5,315,468 discloses that if an antiferromagnetic film is formed of &thgr;-Mn alloy, such as NiMn alloy, which has a face centered tetragonal crystal structure, the exchange coupling field between the antiferromagnetic film and the ferromagnetic film does not deteriorate even in a high temperature range.
Moreover, the inventor has proposed an antiferromagnetic film of IrMn having a face centered cubic crystal structure, which has excellent characteristics. In addition, U.S. Pat. No. 5,315,468 discloses that other &ggr;-Mn alloys, such as MnPt and MnRh, are used as the antiferromagnetic films of the same crystal structure.
However, these antiferromagnetic films are formed of Mn alloy which is difficult to prepare a high density target, so that it is difficult to manage the quality of the film. In addition, when the antiferromagnetic films are laminated on the top of a ferromagnetic film or a spin valve film, the ferromagnetic film or the spin valve film supports an under layer for the antiferromagnetic film, so that the antiferromagnetic film crystal-grows so as to obtain good exchanging coupling characteristics. However, when the antiferromagnetic underlies the ferroelectric film, there is a problem of the selection of the under layer that promotes a crystal growth.
On the other hand, a magnetic storage having a magnetic head, which uses a magnetoresistive element having a dual spin valve film and a magnetoresistive element having a dual spin valve film, is also widely used.
Conventionally, the readout of information recorded in a magnetic recording medium is carried out by a method for moving a read head comprising a magnetic core, onto which a coil is wound and which has a magnetic gap, with respect to a recording medium, and sensing a magnetic field through the magnetic gap at that time to detect a voltage induced in the coil. On the other hand, with the increase of the magnetic recording density, a magnetic head (MR head) utilizing the magnetoresistance effect (MR effect), such as NiFe alloy film, is widely used at present, since it is able to more sensitively recorded information out of a magnetic recording medium.
Recently, in order to more increase the magnetic recording density, high sensitive magnetoresistive elements using a higher sensitive giant magnetoresistance effect (GMR) than those of the MR heads, i.e., GMR elements, are developed. The promising of the GMR elements is a structure called a spin valve structure. This comprises a non-magnetic metal layer sandwiched between two ferromagnetic metal layers. In this structure, when the direction of magnetization of one of the magnetic layers (the free layer) varies with respect to another layer, the magnetization of which is fixed, by a magnetic field from a recording medium, it is possible to obtain information in the magnetic field of the recording medium as a large variation in value of resistance.
In order to obtain a high output using such a spin valve structure, various structures have been proposed. One of them is a structure called a dual spin valve. In this structure, a free layer is arranged between two magnetization fixed layers, the magnetizations of which are fixed in the same direction, via a non-magnetic metal layer. According to this dual spin valve structure, there is an advantage in that it is possible to obtain a higher output than that of a conventional spin valve film having a single magnetization fixed layer.
However, although the above described spin valve structure can obtain a high output, there are problems in that there are some cases where the pinned layer is inverted by the electrostatic discharge (ESD) so that the output can be obtained, and that it is difficult to modify this to obtain the output again. In addition, it is difficult to set the bias point of the element since a great bias magnetic field in the spin valve.
That is, there are some cases where the pinned layer is inverted by the electrostatic discharge (ESD) in the conventional spin valve element. In order to modify the inversion of the pinned layer, there is proposed a circuit for passing a current through the element to add its galvano magnetic field to the pinned layer. However, in the case of the conventional dual spin valve structure, if the current flows through the element to add its galvano magnetic field to the magnetization fixed layer, magnetic fields are applied to two pinned layers in opposite directions to each other, so that the two pinned layers are fixed in opposite directions to each other. However, in the dual spin valve structure, it is not possible to obtain the output due to the variation in magnetic resistance unless the direction of the magnetization of the pinned layer is the same dir
Fuke Hiromi
Fukuzawa Hideaki
Iwasaki Hitoshi
Koui Katsuhiko
Saito Akiko
Heinz A. J.
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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