Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2000-07-27
2003-12-16
Tupper, Robert S. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06665153
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improvement of a magnetic sensor for reading the information recorded in magnetic recording media. More particularly, the invention relates to an improvement of a magnetoresistance element and head, a magnetoresistance sensing system, and a magnetic storing system.
2. Description of the Related Art
In the magnetic recording fields, conventionally, magnetoresistive (MR) read transducers termed the “magnetoresistance (MR) sensors” or “magnetoresistance (MR) heads” have already been developed and actually used. It has been well known that the MR sensors are capable of reading information from the surface of magnetic recording media at high linear densities.
The MR sensors sense magnetic signals by way of the electrical resistance change of MR elements that varies as a function of the strength and orientation of the magnetic flux sensed by read or MR elements. The MR sensors operate on the basis of the well-known anisotropic magnetoresistance (AMR) effect that a component of the electrical resistance of the MR element varies proportional to the square or the cosine one of the angle between the magnetization orientation of the element and the sense current flowing through the element.
The AMR effect was explained in detail in the paper written by D. A. Thompson et al. and entitled “Memory, Storage, and Related Applications”, IEEE Transaction on Magnetics, Vol. MAG-11, No. 4, pp. 1039-1050, July 1975.
With the conventional magnetic sensors using the AMR effect, vertical magnetic bias has been typically applied to suppress the Barkhausen noise. To realize the vertical magnetic bias, proper antiferromagnetic substance, such as FeMn, NiMn, or oxide of Ni, has been often used as the vertically biasing material.
In recent years, more distinctive MR effect termed the “giant MR effect (GMR)” or “spin valve effect” observed in multi-layered MR sensors of specific sorts has been reported. It has been said that the GMR or spin valve effect is caused by the following reason.
Specifically, if the multl-layered MR sensor has a structure comprising a pair of ferromagnetic layers and a nonmagnetic layer disposed between the pair of ferromagnetic layers, the large electrical resistance change of the MR sensor is due to the spin-dependent transmission of conduction electrons between the pair of ferromagnetic layers by way of the nonmagnetic layer and the spin-dependent scattering at their interfaces accompanied by the spin-dependent transmission.
MR sensors using the GMR effect have improved sensitivity compared with those using the AMR effect, increasing the electrical resistance change of the sensors. When the MR sensor has the above-identified structure comprising a pair of ferromagnetic layers and a nonmagnetic layer disposed between the pair of ferromagnetic layers, it has been found that the in-plane electrical resistance of the sensor is proportional to the cosine of the angle between the magnetization orientations of the pair of ferromagnetic layers.
Concrete configurations of the conventional MR sensors or heads using the GMR or spin valve effect have been disclosed in the following publications.
The Japanese Non-Examined Patent Publication No. 2-61572 published in March 1990 disclosed a MR sensor having a multi-layered structure of at least two ferromagnetic layers and an intermediate layer, which generates large electrical resistance change due to antiparallel arrangement of magnetization in the ferromagnetic layers. As the magnetic layers, several ferromagnetic transition metals and alloys are disclosed. An antiferromagnetic layer, which is preferably made of FeMn, may be formed to contact with one of the ferromagnetic layers.
The Japanese Non-Examined Patent Publication No. 4-358310 published in December 1992 disclosed a MR sensor having a multi-layered structure of a pair of ferromagnetic layers and an intervening nonmagnetic layer. In this sensor, when the applied external magnetic field has a value of zero, the magnetization orientations of the pair of ferromagnetic layers are perpendicular to each other. The electrical resistance of the MR sensor varies proportional to the cosine of the angle between the magnetization orientations of the pair of ferromagnetic layers and is independent upon the orientation of the current flowing through the sensor.
The Japanese Non-Examined Patent Publication No. 6-203340 published in July 1994 disclosed a MR sensor having a multi-layered structure of a pair of ferromagnetic layers and an intervening nonmagnetic layer. In this sensor, the magnetization easy axes of the pair of ferromagnetic layers are substantially parallel to each other. When an external magnetic field is applied, the induced magnetization orientations of the pair of ferromagnetic layers are shifted in opposite directions to each other with respect to their magnetization easy axes.
The Japanese Non-Examined Patent Publication No. 9-282618 published in October 1997 disclosed a MR head having a MR or spin valve layer with a multi-layered structure, a pair of domain control layers disposed at each side of the MR layer, and a pair of electrodes disposed on the pair of domain control layers and electrically connected to the MR layer. In this head, the MR layer has a size corresponding to the track width of a magnetic recording medium. The pair of electrodes are partially overlapped with the MR layer. The distance between the pair of electrodes is narrower than the width of the MR layer.
FIG. 1
shows an example of the configuration of the prior-art MR heads, which is a cross-sectional view taken along the Air Bearing Surface (ABS).
As shown in
FIG. 1
, the prior-art MR head
110
comprises a lower shielding layer
101
formed on the surface of a substrate
111
. A lower gap layer
102
is formed on the lower shielding layer
101
. A MR layer
103
and a pair of vertical biasing layers
104
are selectively formed on the lower gap layer
102
.
The MR layer
103
has an approximately trapezoidal cross section, as shown in FIG.
1
. The width of the MR layer
103
is approximately equal to the track width of applicable magnetic recording media (not shown).
The pair of vertical biasing layers
104
are disposed at each side of the MR layer
103
. The inner opposing ends of the biasing layers
104
are respectively overlapped with and contacted with the corresponding inclined ends of the MR layer
103
.
A pair of electrode layers
106
are formed on the pair of biasing layers
104
and the MR layer
103
. The inner opposing ends of the electrode layers
106
are apart from each other by the intervening gap and are contacted with the upper surface of the MR layer
103
, thereby electrically connecting the electrode layers
106
to the layer MR
103
. The middle region of the MR layer
103
in its widthwise direction is exposed through the gap intervening between the electrode layers
106
.
The MR layer
103
, the pair of biasing layers
104
and the pair of electrode layers
106
constitute a MR element
109
.
An upper gap layer
107
is formed on the pair of biasing layers
104
and the exposed MR layer
103
. The exposed middle region of the MR layer
103
is covered with the upper gap layer
107
. An upper shielding layer
108
is formed on the upper gap layer
107
.
The lower shielding layer
101
, the lower gap layer
102
, the MR element
109
, the upper gap layer
107
, and the upper shielding layer
108
constitute the prior-art MR head
110
.
With the prior-art MR head
110
, the inner opposing ends of the electrode layers
106
are disposed to be nearer to the middle of the MR layer
103
than the contacting parts of the vertical biasing layers
104
with the MR layer
103
. In other words, when the centerline of the MR layer
103
, which corresponds to the centerline of applicable magnetic recording media in the tracking direction, is defined as C, as shown in
FIG. 1
, the innermost edges of the electrode layers
106
are located to be nearer than the innermost edges of the biasing layers
1
Choate Hall & Stewart
TDK Corporation
Tupper Robert S.
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