Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2000-12-12
2004-03-23
Miller, Brian E. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C338S03200R, C324S252000
Reexamination Certificate
active
06710985
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetoresistive film which indicates a resistance change in accordance with an external magnetic field strength, a magnetoresistive head for utilizing the resistance change of the magnetoresistive film to detect the external magnetic field strength, and an information regeneration apparatus for regenerating information recorded in a recording medium.
2. Description of Related Art
In recent years, with the spread of computers, a large amount of information has been handled in a daily manner. Such information is recorded on a recording medium by a large number of physical marks, and regenerated by an information regeneration apparatus for reading the mark on the recording medium to regenerate an electric regeneration signal.
A hard disk drive (HDD) is one of the information regeneration apparatuses, and is characterized in that a memory capacity is large and access speed to the information is fast. The HDD is provided with a magnetic disk as the recording medium whose surface is formed of a magnetic material, and a regeneration head for regenerating the information recorded on the magnetic disk. For the magnetic disk, a surface is magnetized for each micro area (one-bit region), and one bit of information is recorded in a form of a magnetization direction of the one-bit region. The regeneration head is disposed in the vicinity of the magnetic disk, and outputs the electric regeneration signal in accordance with a signal magnetic field H
sig
generated from the magnetization of one-bit region of the magnetic disk to regenerate the information recorded on the magnetic disk.
As recording density of the magnetic disk continues to be enhanced year by year, an area of a one-bit region decreases with enhancement of the recording density, and the signal magnetic field H
sig
generated from the one-bit region is weakened. Therefore, the regeneration head for outputting a large regeneration signal is necessary even for this weak signal magnetic field H
sig
. As the magnetic head for outputting the large regeneration signal, a spin valve magnetoresistive head which is a magnetoresistive head utilizing a giant magnetoresistive (GMR) effect starts to be put to practical use in earnest. The spin valve magnetoresistive head will be hereinafter referred to as a SVMR head.
The SVMR head is provided with a spin valve magnetoresistive film as a multilayered film including a free magnetic layer whose magnetization direction changes in accordance with the signal magnetic field H
sig
or another external magnetic field, a nonmagnetic middle layer formed adjacent to the free magnetic layer and provided with conductivity, a pinned magnetic layer formed adjacent to the nonmagnetic middle layer and provided with a magnetization direction fixed in a predetermined direction, and an antiferromagnetic layer formed adjacent to the pinned magnetic layer and constituted of an antiferromagnetic material for fixing the magnetization direction of the pinned magnetic layer. For the magnetoresistive film, sheet resistance &rgr;/t changes with relative angle changes of the magnetization directions of the free magnetic layer and pinned magnetic layer. When the magnetization directions of both layers are matched with each other in opposite directions, the sheet resistance &rgr;/t of the magnetoresistive film is maximized. When the magnetization directions of both layers are matched with each other in the same direction, the sheet resistance &rgr;/t is minimized. Therefore, by knowing the sheet resistance &rgr;/t of the magnetoresistive film, conversely, magnitude and direction of the external magnetic field can be known. A difference between a maximum value and a minimum value of the sheet resistance &rgr;/t will be hereinafter referred to as resistance change &Dgr;&rgr;/t.
The magnetoresistive film is provided with a pair of electrode terminals, and during operation a sense current is passed to the magnetoresistive film from the pair of electrode terminals. While the sense current flows, and when the SVMR head is relatively moved in the vicinity of a magnetic disk, an electric resistivity of the magnetoresistive film successively changes in accordance with the signal magnetic field H
sig
from the magnetic disk, and a regeneration signal provided with an output voltage represented by a product of the electric resistivity and sense current value is outputted. The output of the regeneration signal of the SVMR head is substantially proportional to the resistance change &Dgr;&rgr;/t. In general, since the spin valve magnetoresistive film has a large resistance change &Dgr;&rgr;/t, the SVMR head outputs a high-output regeneration signal.
As one measure for obtaining a higher output from the SVMR head, there is proposed reduction of a height (length in a direction perpendicular to a surface opposite to the magnetic disk) of the magnetoresistive film. By reducing the height, a sectional area of a conductive path for passing the sense current decreases, the resistance change &Dgr;&rgr;/t increases, and the large-output regeneration signal is obtained.
However, since the magnetization direction of the pinned magnetic layer is fixed in the height direction, simply with the reduction of the height, a diamagnetic field of the pinned magnetic layer increases, and the fixing of the magnetization of the pinned magnetic layer is weakened. When the magnetization fixing is weakened, an angle formed by the magnetization directions of the free magnetic layer and pinned magnetic layer of the magnetoresistive film largely deviates from an ideal angle of 90 degrees. With such an angle deviating state, the resistance of the magnetoresistive film fails to linearly respond to a change of the signal magnetic field H
sig
, and symmetry of SVMR head regeneration waveform is deteriorated with respect to a positive
egative signal magnetic field H
sig
. Moreover, the deterioration of symmetry results in a decrease of a dynamic range on either the positive or negative side of the output voltage, and a substantial regeneration output decreases.
In order to decrease the diamagnetic field, known is a magnetoresistive film constituted of a laminated ferri-film in which the pinned magnetic layer is provided with a three-layer structure including a first soft magnetic layer, a second soft magnetic layer, and an antiparallel coupling middle layer, held between the first and second soft magnetic layers, for coupling the magnetizations of the soft magnetic layers to each other substantially in parallel or in opposite directions. In the laminated ferri-film, since the respective magnetizations of the first and second soft magnetic layers are directed and fixed in the opposite directions, the diamagnetic field is weak, and influence of the external magnetic field is hardly exerted, so that even when the height is reduced, the magnetization direction is firmly fixed. Therefore, by employing the laminated ferri-film in the pinned magnetic layer, the high output of the SVMR head can be obtained.
In order to obtain a much higher output from the SVMR head, for example, it is known that thickness of the free magnetic layer or the nonmagnetic middle layer is preferably reduced. This is because by forming these layers to be thin, an excess shunt current flowing through these layers and not contributing to a magnetoresistive effect is depressed and the resistance change &Dgr;&rgr;/t increases.
However, the magnetization of the free magnetic layer of the magnetoresistive film is given, from the magnetization of the pinned magnetic layer, an interlayer coupling field H
in
attributed to interlayer coupling of these magnetizations, and with reduction of the thickness of the free magnetic layer or the nonmagnetic middle layer, this interlayer coupling field H
in
increases. Since the interlayer coupling field H
in
allows the angle formed by the magnetization directions of the free magnetic layer and pinned magnetic layer to deviate from the ideal angle of 90°, with an increase of th
Fujitsu Limited
Greer Burns & Crain Ltd.
Miller Brian E.
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