Metal treatment – Process of modifying or maintaining internal physical... – Magnetic materials
Reexamination Certificate
1999-03-19
2001-08-07
Sheehan, John (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Magnetic materials
C029S603080
Reexamination Certificate
active
06270588
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a magnetoresistive effect (MR) sensor especially using a giant magnetoresistive effect (GMR), such as spin valve effect, to a thin-film magnetic head with the MR sensor used in a HDD (Hard Disk Drive) unit for a computer, and to a manufacturing method of the thin-film magnetic head.
DESCRIPTION OF THE RELATED ART
Recent widespread use of personal computers has increased the popularity of network transmissions of digital information including for not only conventional numerical digital data but also digital image data. Thus, the amounts of information to be treated are dramatically increasing.
In order to process such massive amounts of digital information, it is necessary to use fast microprocessor units (MPU) and fast and reliable HDD units with large capacity. To realize such HDD units, high sensitivity and large output magnetic heads are required.
An anisotropic magnetoresistive effect (AMR) head utilizing an abnormal magnetoresistive effect of a ferromagnetic thin-film layer based upon so-called spin-orbit interaction, wherein electrical resistance of the ferromagnetic layer varies depending upon the electrical field, has been widely known. For example, IEEE Transaction on Magnetics, Vol. MAG-7, No. 1, pp. 150-154, March 1971 discloses such an AMR head.
A thin-film layer of NiFe, NiFeCo, FeCo or NiCo material usually forms the AMR sensor in such a head. However, the relative change in resistance &Dgr;R/R of the NiFe thin-film layer, which exhibits most excellent soft magnetic characteristics among these materials, is merely 2-3 % at most. Thus, it was necessary to develop MR material with a greater magnetoresistance.
In order to satisfy the requirement for high sensitivity and high power magnetic heads, more recently, thin-film magnetic heads with MR sensors based on the spin valve effect of CMR characteristics have been proposed. For example, Physical Review B, Vol.43, No. 1, pp. 1297-1300, Jan. 1991, Journal of Applied Physics, Vol. 69, No. 8, pp. 4774-4779, Apr. 1991, IEEE Transaction on Magnetics, Vol. 30, No. 6, pp. 3801-3806, Nov. 1994, and U.S. Pat. Nos. 5,206,590 and 5,422,571 disclose these heads.
The spin valve effect thin-film structure includes first and second thin-film layers of a ferromagnetic material magnetically separated by a thin-filmlayer of non-magnetic metallicmaterial, and an adjacent layer of anti-ferromagnetic material is formed in physical contact with the second ferromagnetic layer to provide an exchange bias magnetic field by exchange coupling at the interface of the layers. The magnetization direction in the second ferromagnetic layer is constrained or maintained by the exchange coupling, hereinafter the second layer is called the “pinned layer”. On the other hand, the magnetization direction of the first ferromagnetic layer is free to rotate in response to an externally applied magnetic field, hereinafter, the first layer is called the “free layer”. The direction of the magnetization in the free layer changes between parallel and anti-parallel against the direction of the magnetization in the pinned layer, and hence the magneto-resistance greatly changes and the GMR characteristics are obtained.
The output characteristic of the spin valve effect MR sensor depends upon the angular difference of magnetization between the free and pinned ferromagnetic layers. The direction of the magnetization of the free layer is free to rotate in accordance with an external magnetic field. That of the pinned layer is theoretically fixed to a specific direction (referred to as “pinned direction”) by the exchange coupling between this layer and an adjacently formed anti-ferromagnetic layer.
In fact, the spin valve effect MR sensor for the magnetic read head is fabricated by patterning the multi-layered spin valve effect MR sensor in a rectangular shape, by providing to the free layer the axis of easy magnetization along the track-width direction (longitudinal direction), and by providing to the pinned layer the exchange coupling bias magnetization along the sensor-height direction (transverse direction) which is perpendicular to the track-width direction so that magnetization directions of the free and pinned layers are kept orthogonal to each other under no magnetic field environment.
In this kind of spin valve effect MR sensor, the direction of the magnetization of the pinned layer may change or rotate by various reasons as follows.
(1) In general, at both end portions in the track-width direction of the spin valve effect MR sensor, hard magnet layers are formed for providing the longitudinal bias for a static magnetic field to the free layer so as to prevent non-linear magnetization in the free layer and non-reciprocal change in magnetization, called Barkhausen noise, from occuring. However, this longitudinal magnetic bias is applied not only to the free layer but also to the pinned layer causing the magnetization direction of the pinned layer at its both end portions to change or rotate.
(2) A sense current is applied to the spin valve effect MR sensor to flow toward a specific direction (against direction) to produce a magnetic field which will change the magnetization of the free layer to its longitudinal direction. However, since the magnetic field produced by the sense current does not have the same direction as the exchange coupling bias magnetization in the pinned layer, the magnetization direction of the pinned layer will change or rotate.
(3) Furthermore, since the exchange magnetic bias produced between the pinned layer and the anti-ferromagnetic layer has temperature dependency, the applied exchange magnetic bias to the pinned layer will be reduced in magnitude when the temperature of the spin valve effect MR sensor increases. This reduction of the exchange coupling bias may build up the change or rotation of the magnetization direction of the pinned layer.
If the direction of the magnetization changes, the angular difference between the pinned and free layers also changes and, therefore, the output characteristic also changes. Consequently, stabilizing the direction of the magnetization in the pinned layer is very important.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to resolve the aforementioned problems by using a new approach, and to provide an MR sensor, a thin-film magnetic head with the MR sensor and manufacturing method of the thin-film magnetic head, whereby improved output characteristics and an enlarged permissible temperature range can be expected.
According to the present invention, pinned direction and its distribution are determined with consideration of the rotation of magnetization in the pinned layer.
More particularly, a thin-film magnetic head according to the present invention has a spin valve effect multi-layered structure including a non-magnetic electrically conductive material layer, first and second ferromagnetic material layers (free and pinned layers) separated by the non-magnetic electrically conductive material layer, and an anti-ferromagnetic material layer formed adjacent to and in physical contact with one surface of the second ferromagnetic material layer. This one surface is an opposite side of the non-magnetic electrically conductive material layer. The multi-layered structure has ends at its track-width direction. The head also has longitudinal bias means formed at both the track-width ends of the multi-layered structure, for providing a longitudinal magnetic bias to the multi-layered structure. The multi-layered structure and the longitudinal bias means are formed such that an angle between a direction of exchange coupling magnetic bias in the second ferromagnetic material layer produced by the exchange coupling with the anti-ferromagnetic material layer and a direction of the longitudinal magnetic bias in the second ferromagnetic material layer (Hex angle) is more than 90° in at least part of the second ferromagnetic material layer.
The Hex angle, which is the angle between the direction of the exchange coupling magnetic
Oyama Nobuya
Takahashi Masato
Takano Ken-ichi
Armstrong Westerman Hattori McLeland & Naughton LLP
Sheehan John
TDK Corporation
LandOfFree
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