Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1999-12-23
2002-09-24
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S693100, C428S668000, C428S334000, C360S112000, C360S125330
Reexamination Certificate
active
06455178
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an exchange coupling film utilizing the exchange coupling between an antiferromagnetic film and a ferromagnetic film and magnetoresistive elements such as magnetic field sensors and reproducing magnetic heads which are provided with such an exchange coupling film as mentioned above.
2. Description of the Related Art
The study of a magnetic head using a magnetoresistive element as a reproducing head for the sake of high-density magnetic recording has been heretofore studied. At present, a thin film of 80 at %Ni-20 at %Fe alloy (otherwise known as “Permalloy”). is generally used as a magnetoresistive material. As alternatives to this material, artificial lattice films such as of (Co/Cu)n which exhibits a giant magnetoresistive effect and spin valve films have been attracting attention in recent years.
Incidentally, since magnetoresistive films using these materials have magnetic domains, the Barkhausen noise originating by multi-domain activities poses a serious problem in the way to the commercialization the films. Various methods for imparting a single domain to the magnetoresistive films have been being studied from various angles. A method which resides in controlling in a specific direction the domains of a magnetoresistive film by utilizing the exchange coupling between a magnetoresistive film which is a ferromagnetic film and an antiferromagnetic film is counted among these methods. As the antiferromagnetic material used for exchange coupling, a &ggr;-FeMn alloy has been heretofore finding-wide recognition (disclosed in U.S. Pat. No. 4,103,315 and U.S. Pat. No. 5,315,468, for example).
Further, the technique utilizing an exchange coupling between an antiferromagnetic film and a ferromagnetic film for pinning a magnetization of a magnetic film of a spin valve film has been disseminating in recent years. Also for this purpose, a &ggr;-FeMn alloy has been used as an antiferromagnetic material.
The &ggr;-FeMn alloy, however, is deficient in resistance to corrosion, particularly to the corrosion due to water, and is at a disadvantage in suffering the yield of elements being produced to be notably lowered and the force of exchange coupling with a magnetoresistive element to be deteriorated with time as by the corrosion during the course of fabrication of the magnetoresistive element and by the corrosion by the moisture in the air.
The antiferromagnetic film which is made of the &ggr;-FeMn alloy is problematic in respect that the force of exchange coupling with the ferromagnetic film is markedly altered by the temperature environment. Since the temperature of element parts of the magnetic head ultimately rises to the neighborhood of 80° C. during the operation of the magnetic head, the blocking temperature at which the. force of exchange coupling between the ferromagnetic film and the antiferromagnetic film is wholly lost ought to be as high as permissible. Since the blocking temperature of the &ggr;-FeMn alloy system is not higher than 200° C., the antiferromagnetic film under discussion is at a disadvantage in exhibiting only inferior lasting reliability.
U.S. Pat. No. 4,103,315, for example, discloses cases of using antiferromagnetic films made of such &ggr;-Mn alloys as PtMn and RhMn other than the &ggr;-FeMn alloy and also cases of using antiferromagnetic films made of such oxides as NiO. The anti-ferromagnetic films made of such &ggr;-Mn alloys as PtMn and RhMn, however, exhibit no sufficient force of exchange coupling with a ferromagnetic film. In contrast, the antiferromagnetic films made of such oxides as NiO exhibit inferior thermal stability and exhibit unstable force of exchange coupling with a ferromagnetic film at such high temperatures as exceed about 100° C. Further, such oxide systems as NiO exhibit high electric resistance, permit no direct derivation of an electrode therefrom, and entail the disadvantage of complicating the construction of an element.
U.S. Pat. No. 5,315,468 discloses an observation that when an antiferromagnetic film is formed of such a &thgr;-Mn alloy as NiMn which has a face-centered tetragonal (fct) crystal structure, the force of exchange coupling between the antiferromagnetic film and a ferromagnetic film is not degraded even in a range of high temperatures.
The antiferromagnetic film of this nature, as deposited, exhibits a very small force of exchange coupling with a ferromagnetic film and, for the sake of acquiring a fully satisfactory force of coupling, must undergo a heat treatment at a high temperature in the neighborhood of 250° C. by all means. When the antiferromagnetic film of this sort is adopted, therefore, the process of production is complicated to the extent of lowering the yield of production and degrading the reliability of the product.
Antiferromagnetic films have been heretofore used, as described above, for attaining exchange coupling with ferromagnetic films as by abating the Barkhausen noise inherent in magnetoresistive elements. The conventional antiferromagnetic films, however, suffer from deficiency in force of exchange coupling with a ferromagnetic film or in resistance to corrosion particularly at elevated temperatures and incur difficulty in producing exchange coupling films of fully satisfactory reliability with a high yield.
SUMMARY OF THE INVENTION
The purpose of this invention is to clear the problems encountered as described above.
An object is the provision of an exchange coupling film which is provided with an antiferromagnetic film exhibiting ample force of exchange coupling with a ferromagnetic film even in a range of high temperature and, at the same time, excelling in resistance to corrosion, produced by a simple process, and possessed of good reliability and a magnetoresistive element which is provided with the exchange coupling film and enabled to produce stable output for a long time.
A first exchange coupling film according to this invention is an exchange coupling film obtained by laminating an antiferromagnetic film and a ferromagnetic film and characterized in that at least a portion of the antiferromagnetic film has a face-centered cubic crystal structure and made of an IrMn alloy of a composition represented by the general formula, Ir
x
Mn
100−x
, wherein x stands for a value by at % satisfying the expression, 2≦x≦80.
The second exchange coupling film according to this invention is an exchange coupling film obtained by laminating an antiferromagnetic film and a ferromagnetic film and characterized in that the antiferromagnetic film is made of an IrMn alloy of a composition represented by the general formula, Ir
x
Mn
100−x
, wherein x stands for a value by at % satisfying either of the expressions, 2≦x≦35 and 60≦x≦80.
The third exchange coupling film according to this invention is an exchange coupling film obtained by laminating an antiferromagnetic film and a ferromagnetic film and characterized in that the antiferromagnetic film is made of an IrMn alloy of a composition represented by the general formula, (Ir
x
Mn
1−x
,)
100−y
Fe
y
, wherein x′ stands for a value by atomic ratio satisfying the expression, 0.02≦x′≦0.80, and y for a value by at % satisfying the expression, 0≦y≦30.
Then, the magnetoresistive element of this invention is characterized by being provided with such an exchange coupling film as mentioned above and an electrode for feeding an electric current at least to the ferromagnetic film in the exchange coupling film.
To be specific, this invention is characterized by using an IrMn alloy possessed of specific crystal structure and composition for the antiferromagnetic film in the exchange coupling film.
Now, this invention will be described in detail below. The first exchange coupling film according to this invention is provided with a basic structure formed by laminating an antiferromagnetic film made of an IrMn alloy and a ferromagnetic film.
This first exchange coupling film is enabled to acquire an amply large force of exchange
Fuke Hiromi
Funayama Tomomi
Hashimoto Susumu
Iwasaki Hitoshi
Kamiguchi Yuuzo
Foley & Lardner
Jones Deborah
Kabushiki Kaisha Toshiba
LaVilla Michael
LandOfFree
Exchange coupling film and magnetoresistive element does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Exchange coupling film and magnetoresistive element, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Exchange coupling film and magnetoresistive element will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2829838