Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2000-12-04
2004-11-16
Renner, Craig A. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06819533
ABSTRACT:
BACKGROUND OF THE INVENTION
i) Field of the Invention
The present invention relates to a magnetoresistive head for utilizing a resistance change in accordance with an external magnetic field intensity to detect the external magnetic field intensity, and an information regeneration apparatus for regenerating information recorded in a recording medium.
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 usually recorded on a recording medium as 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 generally 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 the one-bit region of the magnetic disk to regenerate the information recorded on the magnetic disk.
A recording density of the magnetic disk continues to be enhanced year by year, an area of the 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, a magnetic 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 is 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 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 external magnetic field, a nonmagnetic layer formed adjacent to the free magnetic layer and provided with conductivity, a pinned magnetic layer formed adjacent to the nonmagnetic layer and having its 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, a resistance change is caused in accordance with a relative angle change of magnetization directions of the free magnetic layer and fixed magnetic layer, a resistivity is minimized when the magnetization directions are directed in the same direction, and the resistivity is maximized when magnetizations are directed in opposite directions. The magnetoresistive film is provided with a pair of electrode terminals, and during operation a sense current is passed through the magnetoresistive film from the pair of electrode terminals. While the sense current flows, and the SVMR head is disposed close to a magnetic disk and relatively moved, an electric resistivity of the magnetoresistive film successively changes in accordance with a signal magnetic field H
sig
from the magnetic disk, and a regeneration signal with an output voltage represented by a product of the electric resistivity and the sense current value is outputted.
An output of the regeneration signal of the SVMR head is substantially proportional to a difference &Dgr;&rgr;/t between a maximum value and a minimum value of a sheet resistance which changes in accordance with the external magnetic field. 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. In general, since the spin valve magnetoresistive film has a large resistance change &Dgr;&rgr;/t, the high-output regeneration signal is outputted by the SVMR head. However, it is demanded that a higher output be obtained from the SVMR head by further increasing the resistance change &Dgr;&rgr;/t. It is known that in order to increase the resistance change &Dgr;&rgr;/t, thickness of the free magnetic layer and nonmagnetic layer may be reduced. When the thickness of the layer is large, an excess shunt current not contributing to the magnetoresistive effect flows in these layers to decrease the resistance change &Dgr;&rgr;/t, but a shunt current amount is suppressed by setting these layers to be thin.
However, in the magnetoresistive film, an interlayer coupling field H
in
attributed to exchange coupling of the magnetizations is applied to the magnetization of the free magnetic layer mainly from the magnetization of the pinned magnetic layer, and with advancement of thinning of the free magnetic layer and nonmagnetic layer, this interlayer coupling field H
in
increases. For example, the resistance change &Dgr;&rgr;/t of the spin valve magnetoresistive film constituted of Ta (50 angstroms)/CoFe (free magnetic layer: 20 angstroms)/Cu (nonmagnetic layer: 30 angstroms)/CoFe (pinned magnetic layer: 20 angstroms)/PtMn (antiferromagnetic layer: 200 angstroms)/Ta (100 angstroms) is about 0.9&OHgr;, but the resistance change &Dgr;&rgr;/t is improved to 1.4&OHgr;, by reducing the thickness of the nonmagnetic layer of Cu to 20 angstroms from 30 angstroms. However, by the thickness reduction, the interlayer coupling field H
in
increases to 2.5 kA/m from 0.4 kA/m.
When the interlayer coupling field H
in
increases in this manner, in a head state, an angle formed by the magnetization directions of the free magnetic layer and pinned magnetic layer fails to ideally form 90 degrees, and a large deviation is caused. In the large deviating state of the angle, the resistance of the magnetoresistive film fails to linearly respond to the change of the signal magnetic field H
sig
, and symmetrical property of regeneration waveform of the SVMR head is deteriorated with respect to positive
egative signal magnetic field H
sig
. Moreover, the deteriorated symmetrical property results in a decrease of a dynamic range to either one of positive and negative sides of the output voltage, and there arises a problem that a substantial regeneration output decreases.
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 head in which an interlayer coupling field H
in
applied to a free magnetic layer is minimized, and an information regeneration apparatus provided with the magnetoresistive head.
Among magnetoresistive heads of the present invention for attaining the aforementioned object, a first magnetoresistive head is provided with a magnetoresistive film being a multilayered film including: a pinned magnetic layer having magnetization whose direction is fixed; a free magnetic layer having magnetization whose direction changes in accordance with an external magnetic field; and a first nonmagnetic layer held by the pinned magnetic layer and the free magnetic layer in a layer thickness direction, and indicating a magnitude of resistance in accordance with an angle formed by the magnetization direction of the pinned magnetic layer and the magnetization direction of the free magnetic layer. The magnetoresistive head detects the magnitude of resistance of the magnetoresistive film to detect a strength of the external magnetic field.
The magnetoresistive head comprises: a second nonmagnetic layer disposed adjacent to the surface of the free magnetic la
Kanai Hitoshi
Noma Kenji
Fujitsu Limited
Greer Burns & Crain Ltd.
Renner Craig A.
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