Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2002-02-04
2004-08-31
Ometz, David (Department: 2653)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S320000
Reexamination Certificate
active
06785099
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to spin valve magnetoresistive sensors for reading information signals from a magnetic medium and, in particular, to a spin valve sensor with high resistance magnetic layers adjacent to the magnetic shields to improve insulation of the magnetoresistive sensor from the conductive shields.
2. Description of the Related Art
Computers often include auxiliary memory storage devices having media on which data can be written and from which data can be read for later use. A direct access storage device (disk drive) incorporating rotating magnetic disks is commonly used for storing data in magnetic form on the disk surfaces. Data is recorded on concentric, radially spaced tracks on the disk surfaces. Magnetic heads including read sensors are then used to read data from the tracks on the disk surfaces.
In high capacity disk drives, magnetoresistive (MR) read sensors, commonly referred to as MR sensors, are the prevailing read sensors because of their capability to read data from a surface of a disk at greater track and linear densities than thin film inductive heads. An MR sensor detects a magnetic field through the change in the resistance of its MR sensing layer (also referred to as an “MR element”) as a function of the strength and direction of the magnetic flux being sensed by the MR layer.
The conventional MR sensor operates on the basis of the anisotropic magnetoresistive (AMR) effect in which an MR element resistance varies as the square of the cosine of the angle between the magnetization in the MR element and the direction of sense current flowing through the MR element. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium (the signal field) causes a change in the direction of magnetization in the MR element, which in turn causes a change in resistance in the MR element and a corresponding change in the sensed current or voltage.
Another type of MR sensor is the giant magnetoresistance (GMR) sensor manifesting the GMR effect. In GMR sensors, the resistance of the MR sensing layer varies as a function of the spin-dependent transmission of the conduction electrons between magnetic layers separated by a non-magnetic layer (spacer) and the accompanying spin-dependent scattering which takes place at the interface of the magnetic and non-magnetic layers and within the magnetic layers.
GMR sensors using only two layers of ferromagnetic material (e.g., Ni—Fe) separated by a layer of non-magnetic material (e.g., copper) are generally referred to as spin valve (SV) sensors manifesting the SV effect.
FIG. 1
shows a prior art SV sensor
100
comprising end regions
104
and
106
separated by a central region
102
. A first ferromagnetic layer, referred to as a pinned layer
120
, has its magnetization typically fixed (pinned) by exchange coupling with an antiferromagnetic (AFM) layer
125
. The magnetization of a second ferromagnetic layer, referred to as a free layer
110
, is not fixed and is free to rotate in response to the magnetic field from the recorded magnetic medium (the signal field). The free layer
110
is separated from the pinned layer
120
by a non-magnetic, electrically conducting spacer layer
115
. Hard bias layers
130
and
135
formed in the end regions
104
and
106
, respectively, provide longitudinal bias for the free layer
110
. Leads
140
and
145
formed on hard bias layers
130
and
135
, respectively, provide electrical connections for sensing the resistance of SV sensor
100
. IBM's U.S. Pat. No. 5,206,590 granted to Dieny et al., incorporated herein by reference, discloses a GMR sensor operating on the basis of the SV effect.
FIG. 2
shows a prior art read back head
200
incorporating an SV sensor. Referring to
FIG. 2
, the spin valve sensor
100
is sandwiched between nonmagnetic insulative first and second read gap layers
202
and
204
, and the read gap layers are sandwiched between ferromagnetic first and second shield layers
206
and
208
. The separation between the first and second shield layers
206
and
208
defines the read gap
210
. The ferromagnetic first and second shield layers
206
and
208
are needed to shield the sensor
100
from stray magnetic fields. The nonmagnetic insulative first and second read gap layers
202
and
204
provide electrical insulation of the sensor
100
from the metallic ferromagnetic shield layers
206
and
208
.
A problem with the prior art sensors arises as the size of the read head is decreased in order to address the need for higher storage density disk files. As the read gap is made ultrathin, the insulative properties of the first and second read gap layers is reduced leading to possible shorting of the magnetoresistive sensor to the metallic shields. Therefore there is a need for improved insulation of the read sensor from the shields for read heads having ultrathin magnetic read gaps in order to read magnetic data at higher storage densities.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to disclose a magnetic read head having ultrathin read gap layers with improved insulative properties between a magnetoresistive sensor and ferromagnetic shield layers.
It is another object of the present invention to disclose a magnetic read head having improved electrical insulation of the magnetoresistive sensor from the shields without increasing the magnetic read gap.
It is a further object of the present invention to disclose a magnetic read head having reduced smearing and telegraph noise by keeping metallic parts of the shields at an increased distance from the magnetoresistive sensor.
In accordance with the principles of the present invention, there is disclosed a preferred embodiment of the present invention wherein first and second shield cap layers made of high resistivity permeable magnetic material are formed between the first and second ferromagnetic shields and the first and second insulative read gap layers, respectively, of a magnetoresistive read head. In the preferred embodiment, the read head comprises a first shield cap layer of iron hafnium oxide (Fe—Hf—O
x
), or alternatively, manganese zirconium ferrite (Mn—Zn ferrite) disposed between the first ferromagnetic shield and the first insulative read gap layer, a spin valve sensor sandwiched between the read gap layer and a second insulative read gap layer, and a second shield cap layer of Fe—Hf—O
x
, or alternatively, Mn—Zn ferrite disposed between the second read gap layer and a second ferromagnetic shield.
The Fe—Hf—O
x
material, or alternatively, the Mn—Zn ferrite material provide highly resistive or insulating soft ferromagnetic layers which add to the electrically insulative read gap layers to provide increased electrical insulation of the spin valve sensor from the metallic ferromagnetic shields while not adding to the magnetic read gap of the read head. The extra insulation provided by the highly resistive shield cap layers makes it possible to use ultrathin insulative first and second gap layers without increased risk of electrical shorting between the spin valve sensor and the ferromagnetic first and second shields.
The above, as well as additional objects, features and advantages of the present invention will become apparent in the following detailed written description.
REFERENCES:
patent: 5206590 (1993-04-01), Dieny et al.
patent: 6385015 (2002-05-01), Narumi et al.
patent: 6452761 (2002-09-01), Carey et al.
patent: 6643105 (2003-11-01), Nakamoto et al.
patent: 2001/0038517 (2001-11-01), Kamijima
patent: 2002/0075609 (2002-06-01), Terunuma
patent: 2001-56914 (2003-02-01), None
Lee Wen-Yaung
Lin Tsann
Mauri Daniele
Gill William D.
Hitachi Global Storage Technologies - Netherlands B.V.
Nunnelley Lewis L.
Ometz David
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