Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1997-10-09
2001-04-10
Letscher, George J. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06215631
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetoresistive effect film which is used in a magnetoresistive effect element which reads the magnetic field strength from a magnetic recording medium or the like as a signal, and more specifically to magnetoresistive effect film that has a large resistance change ratio in a small external magnetic field.
2. Description of Related Art
In recent years, transducers known as MR (magnetoresistive) sensors (or MR heads) have been developed which read data from a magnetic surface with a high linear density.
By means of a reading element, an MR sensor performs detection of a magnetic field signal via a change of resistance, which is a function of the magnetic flux strength and direction.
In an MR sensor Such as this in the past, one component of the resistance of the reading element changed in proportion to the square of the cosine of the angle formed between the direction of the magnetization and the detection current flowing in the element, according to an operating principle known as the anisotropic magnetoresistance (AMR) effect. The AMR effect is discussed in detail in D. A. Thompson et al “Memory, Storage, and Related Applications” IEEE Transactions of Magnetics. MAG-11, p. 1039 (1975).
Additionally, there has recently been a report of a more prominent magnetoresistive effect, whereby the resistance change in a laminated magnetic sensor is attributed to spin dependency transmission between magnetic layers with an intervening non-magnetic layer, and to accompanying spin dependency dispersion at the layer boundary.
This magnetoresistive effect is known by a variety of names, including “giant magnetoresistive effect” and “spin valve effect”.
A magnetoresistive sensor such as this is made from an appropriate material, and provides an improvement in density and increase in resistance change when compared to observation by a sensor which uses the AMR effect. With this type of MR sensor, the internal planar resistance between a pair of antiferromagnetic layers that are separated by a non-magnetic layer varies in proportion to the cosine of the angle formed between the magnetization directions in the two layers.
In the Japanese Unexamined Patent Publication No. 2-61572, there is description of a laminated magnetic structure which brings about a large MR effect, that occurs by means of anti-parallel orientation of the magnetization between the magnetic layers.
In the above-noted Japanese unexamined patent application publication, transition metals and alloys thereof are cited as materials that can be used in the magnetic layers in this laminated structure. There is disclosure that FeMn is suitable for use as at least one of two magnetic layers that are separated by a center layer.
In the Japanese Unexamined Patent Publication No. 4-358310, there is a disclosure of an MR sensor having a two layers of thin film ferromagnetic material which are separated by a non-magnetic metallic thin film, in which when the applied magnetic field is zero the magnetization directions in the two ferromagnetic thin films are mutually perpendicular, the resistance between the two non-coupled ferromagnetic layers varying in proportion to the cosine of the angle formed between the magnetization directions in the two layers, this being independent of direction of current flow in the sensor.
In the Japanese Unexamined Patent Publication No. 6-214837, there is a disclosure of magnetoresistive effect element in which, onto a substrate a plurality of magnetic thin films are laminated via an intervening non-magnetic layer, wherein one soft magnetic thin film which adjacently arranged to each other, via an intervening non-magnetic thin film, is provided with an antiferromagnetic thin film, and further wherein in the magnetoresistive effect film in which the bias magnetic field on this antiferromagnetic thin film is Hr and the coercivity of the soft magnetic thin film is Hc2 (<Hr), the above-noted antiferromagnetic thin film is a super lattice selected as at least two types from the group consisting of NiO, NixCo1-x 0, and CoO.
Additionally, in the Japanese Unexamined Patent Publication No. 7-136670 in a magnetoresistive effect film having the same structure as in the Japanese Unexamined Patent Publication No. 6-214837, there is a disclosure of a magnetoresistive effect element that is a two-layer film wherein onto a antiferromagnetic thin film of NiO, is laminated a layer of CoO to a thickness of 10 to 40 Å.
However, in a magnetoresistive effect element in the past such as noted above, the following problems existed.
(1) Although operation is by means of a small external magnetic field, a practically usable sensor or magnetic head must have a signal magnetic field applied in the direction of its easy axis, this leading to the problems that, for use as a sensor, there is no change in resistance exhibited in the area of a zero magnetic field, and that there is a non-linearity occurring due to effects such as the Barkhausen jump.
(2) There is ferromagnetic Interaction between a magnetic layers which neighbor one another via an intervening non-magnetic layer, causing the problem of a shift of linear region of the MR curve away from the zero field.
(3) It is necessary to use a material such as FeMn, which is subject to corrosion, as the antiferromagnetic thin film, making it necessary to take measures in a practically usable device such as using an additive or applying a protective film.
(4) In the case in which a nickel oxide film, which has good resistance to corrosion, is used as the antiferromagnetic thin film, the bias magnetic field is small, and the coercivity of a neighboring soft magnetic film becomes large, leading to the difficulty in achieving magnetization antiparallelness between magnetic layers.
(5) In the case of using a nickel oxide film, the blocking temperature (at which the bias magnetic field is lost) is low, so that if heat treatment is done at 250° C. or above, the bias magnetic field is reduced.
(6) In the case in which an oxide antiferromagnetic film is used as the antiferromagnetic film, oxidation of adjacent soft magnetic films occurs when heat treatment is done, resulting in a reduction of the resistance change ratio in the magnetoresistive effect film.
(7) Because the structure basically obtains a change in resistance by using the change in the mean free path of conducting electrons in a three-layer structure of a magnetic thin film, a non-magnetic thin film and another magnetic thin film, compared with a magnetoresistive effect film known as a coupling type, which has a multiple layer structure, the resistance change ratio is small.
An object of the present invention is to provide a magnetoresistive effect film which exhibits a large linear resistance change in the region of zero magnetic field, and which has good immunity to both corrosion and heat.
A magnetoresistive effect film according to the present invention minimally has a lamination of an antiferromagnetic thin film, a first magnetic thin film (soft magnetic thin film) which makes contact with the above-noted antiferromagnetic thin film, a non-magnetic thin film which makes contact with the first magnetic thin film, and a second magnetic thin film (soft magnetic thin film) which makes contact with the above-noted non-magnetic thin film, wherein if the bias magnetic field of the above-noted antiferromagnetic thin film is Hr and the coercivity of the above-noted second magnetic thin film is Hc2, the equation of Hc2 <Hr should be fulfilled:
The antiferromagnetic thin film, the first magnetic thin film, the non-magnetic thin film, and the second magnetic thin film can be laminated onto a substrate in this sequence, starting with the antiferromagnetic thin film, and an also be laminated onto a substrate in the reverse sequence, starting with the second magnetic thin film. The above-noted antiferromagnetic thin film is a laminate of a nickel oxide film and an iron oxide film having a thickness in the range 20 to 100 Å.
By virtue of
Fujikata Junichi
Nakada Masafumi
Foley & Lardner
Letscher George J.
NEC Corporation
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