Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2000-06-07
2001-06-19
Letscher, George J. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06249405
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to magnetic storage/read systems and more particularly to a magnetic storage/read system having a high recording density.
A prior art magnetic storage/read system in which metallic magnetic and nonmagnetic films having different magnetic properties are stacked is disclosed in
Journal of the Physical Society of Japan,
Vol. 59, No. 9, September 1990, pp. 3061-3064.
Also disclosed in
Physical Review B,
Vol. 43, No. 1, Jan. 1, 1991, pp. 1297-1300, is another prior art magnetic storage/read system in which an FeMn antiferromagnetic film is laminated with a ferromagnetic film, a nonmagnetic film and a ferromagnetic film.
JP-A-2-61572 discloses a magnetic field sensor which uses a ferromagnetic thin film separated by an interlayer and an antiferromagnetic thin film adjacent to one side of the ferromagnetic thin film.
Further disclosed in JP-A-2-23681 is a multilayer film which comprises a ferromagnetic thin layer having magnetoresistive effects and a metallic conductive thin layer.
In the prior art techniques, it has been difficult to realize a magnetic storage/read system having a high recording density and particularly a function as a storage device comprising a magnetoresistive element which provides sufficient sensitivity and output in response to an applied field.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a magnetic storage/read system which has a high recording density.
In accordance with an aspect of the present invention, a magnetic storage/read system, which in use is connected to an external device such as a computer, comprises preferably a recording medium for magnetically storing a signal, an electric-magnetic transducer opposing the recording medium, means for rotating the recording medium relative to the electric-magnetic transducer, and means for moving the electric-magnetic transducer to a predetermined position relative to the recording medium. It is more desirable that the magnetic storage/read system further comprises an interface circuit through which the system is connected to an external data processor and a circuit for processing signals stored on the recording medium.
The recording medium used in the present invention refers to a so-called magnetic disk which has a magnetic film for magnetically storing signals thereon, a substrate and a protective layer. The signal to be recorded on the recording medium may be recorded longitudinally in or perpendicularly to the plane of the recording medium. The magnetic film of the recording medium is required to have a coercivity that can magnetically hold the signals thereon.
The electric-magnetic transducer used in the present invention refers to a so-called magnetic head which can record signals on the recording medium or reproduce signals recorded thereon. The magnetic head used in the present invention is a dual type head having separate write and read heads. In particular, the read head preferably comprises a magnetoresistive head which detects a leakage magnetic field from the recording medium and reproduces the detected field in the form of a change in an electric resistance.
The magnetoresistive head is also referred to as a magnetoresistive element. The magnetoresistive element used in the present invention preferably comprises a magnetoresistive film for detecting a leakage magnetic field from the recording medium, a domain control film for controlling a magnetic domain created in the magnetoresistive film, a shunt film for applying a magnetic field for prescribing the magnetic driving range of the magnetoresistive film in a specific direction, and a soft magnetic film. In this case, the shunt film refers to an electrically conductive film formed adjacent to the magnetoresistive film such as a tantalum film or a copper film, and acts to apply a magnetic field generated by a current flowing therethrough to the magnetoresistive film. Similarly, the soft magnetic film refers to a soft magnetic film separated from the magnetoresistive film by a nonmagnetic film, and acts to apply to the magnetoresistive film a bias field generated by static coupling at an edge of the magnetoresistive film. These films do not physically contribute to the magnetoresistive effect per se but merely control the magnetization direction of the magnetoresistive film.
In accordance with an aspect of a magnetic storage/read system of the present invention, a magnetoresistive element in the magnetic storage/read system is made of a substrate, an antiferromagnetic film, a magnetic film, a nonmagnetic conductive film, a soft magnetic film, a nonmagnetic conductive film, a magnetic film and an antiferromagnetic film which are sequentially layered on said substrate, and said magnetoresistive element is driven relative to said medium in the longitudinal direction of the recording medium.
The antiferromagnetic film is made preferably of nickel oxide, but may be made of iron-manganese alloy, chromium-manganese alloy or chromium-aluminum alloy, or may be made of a hard magnetic material such as cobalt-platinum alloy or iron-cobalt-terbium alloy. The hard magnetic film is assumed to have a property that it is difficult to change its magnetization with an applied field and to have a coercivity of, e.g., above 100 Oe. Then, even when 50 Oe of magnetic field is applied, the direction of the magnetization of the hard magnetic film will not be substantially changed. Therefore, the hard magnetic film has an effect similar to that of the antiferromagnetic film. That is, the hard magnetic film has a property that when it contacts another magnetic film, it can apply unidirectional anisotropy based on the exchange coupling bias effect. It is not necessary to use an antiferromagnetic film, and instead a film generally called a bias film may be used.
The ferromagnetic film is made preferably of an alloy of 70-95 atomic % of Ni, 5-30 atomic % of Fe and 1-5 atomic % of Co or made of an alloy of 30-85 atomic % of Co, 2-30 atomic % of Ni and 2-50 atomic % of Fe. The ferromagnetic film may be also made of Permalloy or Permendur alloy. In other words, any material that is ferromagnetic and has a good soft magnetic property can be preferably employed for the ferromagnetic film.
The nonmagnetic film is made preferably of any one selected from the group of Au, Ag and Cu. The film may be made of Cr, Pt, Pd, Ru, Rh or an alloy thereof. That is, any material that does not have a spontaneous magnetization property at room temperature and has a high electron transmission property is preferably used as the material of the nonmagnetic film. The film has a thickness of preferably about 2-1000 Å.
Further, in place of the nonmagnetic conductive film, a very thin nonmagnetic insulating film may be used. In other words, this film is only required to allow electron movement between the magnetic films, such that an electron tunneling effect through a nonmagnetic insulating film may be employed if necessary. In the latter case, it is necessary to make the nonmagnetic insulating film thin enough to enable the electron tunneling effect. The nonmagnetic insulating film is formed to have a thickness of generally below 100 Å and preferably below 50 Å. The nonmagnetic insulating film may be formed preferably as a surface oxide of the soft magnetic film or as an aluminum oxide layer on a metallic film such as an aluminum film additionally formed on the soft magnetic film. The nonmagnetic insulating film may be made of alumina as necessary. In other words, a film having a property of interrupting the magnetic coupling between the magnetic films is preferably used as the nonmagnetic insulating film.
The substrate is used as a base for formation of the above films and acts preferably as a slider for the magnetic disk. The material of the substrate is preferably a ceramic such as stabilized zirconia and alumina, or silicon.
The magnetoresistive element having such a film structure as mentioned above has a property that its electric resistance varies with a very weak magnetic field app
Arai Reiko
Fukui Hiroshi
Fuyama Moriaki
Hoshiya Hiroyuki
Mitsuoka Katsuya
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Letscher George J.
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