Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1999-11-15
2002-07-30
Klimowicz, William (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S324120
Reexamination Certificate
active
06426853
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a magnetoresistive effect (MR) sensor used for various magnetic detection, especially utilizing giant magnetoresistive effect (GMR) such as spin valve magnetoresistive effect (SVMR) or utilizing tunneling magnetoresistive effect (TMR), to a thin-film magnetic head used in a-magnetic record and/or reproduction device such as a HDD (Hard Disk Drive) unit, and to a thin-film wafer with a plurality of the thin-film magnetic heads.
DESCRIPTION OF THE RELATED ART
Recent growth rate of the recording density in magnetic recording is remarkable, for example, 100% of the average annual growth rate may be achieved. Increasing conversion efficiency in thin-film magnetic heads supports this growth in the recording density. A MR conversion rate of a thin-film magnetic head utilizing an anisotropic magnetoresistive effect (AMR) was merely about 2% at most. Whereas the MR conversion rate of a thin-film magnetic head with a SVMR sensor that is one of GMR sensors exhibiting high sensitivity and high power is 6-8%. This is about three times of that of the AMR head.
The SVMR head has a structure with first and second thin-film layers of a ferromagnetic material magnetically separated by a thin-film layer of non-magnetic metallic material, and a layer of anti-ferromagnetic material is formed in physical contact with the second ferromagnetic layer to provide exchange bias magnetic field by exchange coupling at the interface surface 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 “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 “free layers”. 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 GMR characteristics are obtained.
The output characteristic of the SVMR head depends upon the angular difference of magnetization between the free and pinned 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 (called as “pinned directions”) by the exchange coupling between this layer and adjacently formed anti-ferromagnetic layer.
During operation of the SVMR head, it is required that the magnetization direction in the free layer changes without accompanying domain wall movement. This is because the magnetization change accompanied by domain wall movement is non-reciprocal change and responds slower than that accompanied by no domain wall movement, and therefore produces a noise called as Barkhausen noise. Thus, in general, hard magnet layers are arranged at the both end portions of the SVMR structure, for providing bias magnetic field or longitudinal bias to the free layer so as to prevent domain wall movement from occurring.
In such SVMR head, if the magnetization direction in the pinned layer changes in accordance with some externally applied magnetic field, the magnetization direction in the free layer also changes under the influence of this magnetization direction change in the pinned layer so as to vary its output voltage. In fact, a composite type thin-film magnetic head with a SVMR sensor element and an inductive writing element tends to cause two state problems in which the output voltage of the head after writing operation takes two values. It is guessed that such two state problems are caused by change of the magnetization direction in the pinned layer due to applied writing magnetic field from the inductive element.
Since the magnetization direction in the free layer is not completely in parallel with the surface of the magnetic recording medium but inclines toward the magnetic recording medium, the asymmetry characteristics of the SVMR head when it is off-tracked is greatly shifted to the negative side. This inclination is especially large at the track edge regions. If the asymmetry characteristics shifts to the negative side greatly, servo control for controlling the position of the SVMR head to the track center by servo signals recorded on the magnetic recording medium cannot be accurately carried out.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a MR sensor, a thin-film magnetic head and a thin-film wafer with the thin-film magnetic heads, whereby instability of output characteristics such as two state problems can be resolved.
Another object of the present invention is to provide a MR sensor, a thin-film magnetic head and a thin-film wafer with the thin-film magnetic heads, whereby improved asymmetry characteristics can be expected.
According to the present invention, a MR sensor, a thin-film magnetic head and a thin-film wafer with a plurality of the thin-film magnetic heads has a MR multi-layered structure including a non-magnetic material layer, first and second ferromagnetic material layers (free and pinned layers) separated by the non-magnetic material layer, and an anti-ferromagnetic material layer formed adjacent to and in physical contact with one surface of the pinned layer, the one surface being in opposite side of the non-magnetic material layer, the multi-layered structure having ends in a direction parallel to a magnetically sensitive surface or an air bearing surface (ABS), and longitudinal bias means formed at both the ends of the MR multi-layered structure, for providing a longitudinal magnetic bias to the MR multi-layered structure. Particularly, according to the present invention, the MR multi-layered structure is shaped such that a magnetization direction of the pinned layer is inclined an angle from an axis of easy magnetization of the pinned layer.
Since the magnetization direction of the pinned layer forms an angle with respect to the easy axis of the pinned layer, the magnetization direction of the pinned layer becomes easy to return even if external magnetic field is applied thereto. Therefore, instability of output characteristics such as two state problems that will be induced by applied external magnetic field, for example writing magnetic field, can be effectively resolved.
It is preferred that the magnetization direction of the pinned layer is inclined an angle toward a direction opposite to or the same direction as a direction of the longitudinal magnetic bias from the easy axis of the pinned layer.
If the magnetization direction of the pinned layer is inclined an angle of larger than 0 degree from the easy axis of this pinned layer, improved stability of output characteristics may be obtained. In fact, this angle is preferably determined to an angle of equal to or larger than 2 degrees, more preferably to an angle of equal to or larger than 5 degrees. If this angle is too large, the output voltage will decrease. Thus it is preferred that this angle is determined to an angle of equal to or smaller than 60 degrees.
According to the present invention, furthermore, a MR sensor, a thin-film magnetic head and a thin-film wafer with a plurality of the thin-film magnetic heads in which interface surfaces between the MR multi-layered structure of GMR or TMR and the longitudinal bias means are inclined an angle from a direction perpendicular to the magnetically sensitive surface or the ABS. In other words, the end faces in the track-width direction, of the MR multi-layered structure are not perpendicular to the ABS or the magnetically sensitive surface but inclined the angle toward the longitudinal bias means or the track-width direction in case of a magnetic head. Since the end faces of the MR multi-layered structure are inclined, the end faces of the pinned layer also inclined.
Thus, the shape anisotropy of the pinned layer due to the inclination of its end faces and the layer anisotropy of the pin
Iwai Yuzuru
Sakai Masanori
Takano Ken-ichi
Armstrong Westerman & Hattori, LLP
Klimowicz William
TDK Corporation
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