Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Reexamination Certificate
2000-11-30
2004-07-06
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
C428S692100, C428S911000, C360S314000, C360S324000, C360S324100, C427S129000, C427S457000
Reexamination Certificate
active
06759120
ABSTRACT:
BACKGROUND OF THE INVENTION
i) Field of the Invention
The present invention relates to a magnetoresistive film whose resistance changes in accordance with a magnetic field intensity, a magnetoresistive head for detecting the magnetic field intensity in accordance with the resistance change of the magnetoresistive film, an information regeneration apparatus for regenerating information recorded in a recording medium, and a magnetoresistive film manufacture method for manufacturing the magnetoresistive film.
ii) Description of Related Art
In recent years, with spread of a computer, 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 an 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.
At present, in many of the regeneration heads mounted on the HDD, a magnetoresistive head (MR head) including a magnetoresistive film whose resistance changes in accordance with the magnetic field from the outside is used. In the MR head, a pair of electrode terminals are disposed on La the magnetoresistive film, and during operation a sense current is passed to the magnetoresistive film from the pair of the electrode terminals. In such sense current flow state, when the MR head is relatively moved in the vicinity of the 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 high-output regeneration signal with a voltage of a value represented by a product of the electric resistivity and the sense current value is outputted.
However, a recording density of the magnetic disk continues to be enhanced year by year, an area of one-bit region decreases with enhancement of the recording density, the signal magnetic field H
sig
generated from the one-bit region is weakened, and the regeneration head for outputting a large regeneration signal is therefore necessary even for this weak signal magnetic field H
sig
. As the regeneration head for outputting the large regeneration signal, a spin valve magnetoresistive head which is a magnetoresistive head utilizing a giant magnetoresistive (GMR) effect is disclosed by Japanese Patent Application Laid-Open No. 358310/1992, and practical use is starting in earnest.
The spin valve magnetoresistive head is provided with a spin valve magnetoresistive film as a multilayered film including a free magnetic layer (free layer) whose magnetization direction changes in accordance with the external magnetic field, a middle layer formed adjacent to the free layer and constituted of a nonmagnetic metal, a pinned magnetic layer (pinned layer) whose magnetization direction is fixed in a predetermined direction, and an antiferromagnetic layer formed adjacent to the pinned layer and constituted of an antiferromagnetic material for fixing the magnetization direction of the pinned layer. For the magnetoresistive film, when the external magnetic field changes, the magnetization direction of the free layer of the magnetoresistive film changes, and a resistance change is a generated in accordance with relative angle changes of the magnetization directions of the pinned layer and free layer.
Since an output of the regeneration signal of the magnetoresistive head provided with the magnetoresistive film is substantially proportional to a difference &Dgr;&rgr;/t between a maximum value and a minimum value of a sheet resistance changing in accordance with the external magnetic field change, with respect to the magnetoresistive effect, an ability of the magnetoresistive film is evaluated by this difference &Dgr;&rgr;/t in many cases. The difference &Dgr;&rgr;/t between the maximum value and the minimum value of the changing sheet resistance will be hereinafter referred to as resistance change &Dgr;&rgr;/t. Since the aforementioned spin valve magnetoresistive film has a large resistance change &Dgr;&rgr;/t, the high-output regeneration signal can be obtained from the magnetoresistive head provided with the magnetoresistive film.
The spin valve magnetoresistive head outputs the high-output regeneration signal in this manner, but it is demanded that a higher output be obtained by further increasing the resistance change &Dgr;&rgr;/t of the magnetoresistive film. As a measure for increasing the resistance change &Dgr;&rgr;/t, a thickness of the middle layer is reduced. When the thickness of the middle layer is too large, an excess shunt current not contributing to the magnetoresistive effect flows in the middle layer to decrease the resistance change &Dgr;&rgr;/t, but the decrease of the resistance change &Dgr;&rgr;/t is suppressed by setting the middle layer to be thin.
However, in the conventional magnetoresistive film, an interlayer coupling field Hen usually acts between the magnetization of the free layer and the magnetization of the pinned layer to set these magnetization directions to be the same direction, and with further thinning of the middle layer, the coupling field H
in
increases. In the following, the coupling field H
in
has a positive value when the magnetization directions are set to be the same direction, and has a negative value when the directions are set to be directions opposite to each other. By this coupling field H
in
, a deviation is generated in an angle formed by the magnetization direction of the free layer and the magnetization direction of the pinned layer.
In general, the resistivity of the magnetoresistive film preferably linearly changes with respect to the change of the signal magnetic field H.,g from the magnetic disk, and to realize this linear change, it is ideal to form an angle of 90° C. by the magnetization directions of the pinned layer and free layer in the absence of the signal magnetic field H
sig
. However, when the angle deviates from 90° by the coupling field H
in
, the output voltage of the spin valve magnetoresistive head fails to linearly respond to an input of signal magnetic field H
sig
, and strain of a regeneration waveform of the output voltage or another trouble occurs.
SUMMARY OF THE INVENTION
The present invention has been developed in consideration of the aforementioned situations, and an object thereof is to provide a magnetoresistive film in which increase of coupling field with thickness reduction of a middle layer is inhibited, a magnetoresistive head provided with the magnetoresistive film, an information regeneration apparatus provided with the magnetoresistive head, and a magnetoresistive film manufacture method for manufacturing the magnetoresistive film.
Among magnetoresistive films of the present invention for attaining the aforementioned object, a first magnetoresistive film is a multilayered film including: a pinned magnetic layer having magnetization whose direction is fixed; a nonmagnetic middle layer formed on the pinned magnetic layer; and a free magnetic layer formed on the middle layer and provided with magnetization whose direction changes in accordance with an external magnetic field, and indicates a magnitude of resistance in accordance with an angle formed
Aoshima Ken-ichi
Jongill Hong
Kanai Hitoshi
Kane Junichi
Noma Kenji
Greer Burns & Crain Ltd.
Thibodeau Paul
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