U.S. patent application number 09/789670 was filed with the patent office on 2001-07-05 for magnetic head and magnetic storage apparatus using the same.
Invention is credited to Maruyama, Yoji, Nakatani, Ryoichi, Suzuki, Yoshio, Takano, Hisashi.
Application Number | 20010006443 09/789670 |
Document ID | / |
Family ID | 26448414 |
Filed Date | 2001-07-05 |
United States Patent
Application |
20010006443 |
Kind Code |
A1 |
Maruyama, Yoji ; et
al. |
July 5, 2001 |
Magnetic head and magnetic storage apparatus using the same
Abstract
It is the object of the invention to provide a magnetic head and
a magnetic storage apparatus using the magnetic head provided with
a signal reproducing means which is capable of using the same
signal processing circuit as used for the conventional longitudinal
magnetization film type recording medium even when a perpendicular
magnetization film type recording medium is used. Because the
present invention renders the reproducing signal generated from a
perpendicular magnetization film Gaussian shaped (Lorentzian
pulse), the same signal processing circuit as used for the
conventional longitudinal magnetization film type recording medium
can be used. To accomplish this object, in the reproducing means
which is the component of the information reproducing component of
the magnetic head, the first spin valve element and the second
valve element are piled up, the magnetization direction of pinned
layers of both elements is prescribed so as to be antiparallel each
other, and lead electrodes of both elements are connected so as to
be common. When two spin valve elements are piled up to compose a
reproducing means, the first spin valve element is structured so as
to have an Ru film between the first ferromagnetic film and the
second ferromagnetic film and so as to have a Cu film between the
second ferromagnetic film and the third ferromagnetic film, and the
second spin valve element is structured so as to have a Cu film
between the fourth ferromagnetic film and the fifth ferromagnetic
film. These two elements are piled up with interposition of a
desired spacer film adjacently.
Inventors: |
Maruyama, Yoji; (Iruma-shi,
JP) ; Suzuki, Yoshio; (Tokyo, JP) ; Nakatani,
Ryoichi; (Akiruno-shi, JP) ; Takano, Hisashi;
(Kodaira-shi, JP) |
Correspondence
Address: |
KENYON & KENYON
1500 K STREET, N.W., SUITE 700
WASHINGTON
DC
20005
US
|
Family ID: |
26448414 |
Appl. No.: |
09/789670 |
Filed: |
February 22, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09789670 |
Feb 22, 2001 |
|
|
|
09065868 |
Apr 24, 1998 |
|
|
|
Current U.S.
Class: |
360/314 ;
G9B/5.131 |
Current CPC
Class: |
G11B 5/3954 20130101;
G11B 2005/3996 20130101; B82Y 25/00 20130101; G11B 5/035 20130101;
G11B 5/02 20130101; B82Y 10/00 20130101; G11B 2005/0029
20130101 |
Class at
Publication: |
360/314 |
International
Class: |
G11B 005/39 |
Foreign Application Data
Date |
Code |
Application Number |
May 29, 1997 |
JP |
9-139651 |
Apr 25, 1997 |
JP |
9-108564 |
Claims
What is claimed is:
1. A magnetic head comprising: a first spin valve element; a second
spin valve element; and a non-magnetic spacer layer formed between
the first spin valve element and the second spin valve element; the
first spin valve element including: a first antiferromagnetic film
a first ferromagnetic film; a first non-magnetic film; a second
ferromagnetic film; a second non-magnetic film of which
magnetization direction can be rotated in respect to an external
magnetic field; and a first soft magnetic film; the second spin
valve element including: a second antiferromagnetic film; a third
ferromagnetic film; a third non-magnetic film; and a second soft
magnetic film of which the magnetization direction can be rotated
in respect to an external magnetic field; wherein: the
magnetization direction of the first ferromagnetic film and the
magnetization direction of the second ferromagnetic film are in an
antiparallel state; the magnetization direction of the second
ferromagnetic film and the magnetization direction of the third
ferromagnetic film are in an antiparallel state; and the first soft
magnetic film and the second soft magnetic film are arranged to be
symmetrical with respect to the non-magnetic spacer layer.
2. A magnetic head according to claim 1, wherein said first
non-magnetic medium layer consists of any one of metal layers
selected from a group of Ru, Rh, Ir, Cr, and Cu or consists of an
alloy containing some of these metals.
3. A magnetic head according to claim 1, wherein said second
non-magnetic film and said third non-magnetic film comprise a Cu
layer.
4. A magnetic head according to claim 1, wherein the product of the
film thickness and saturation magnetization of said first
ferromagnetic film is larger than the product of the film thickness
and saturation magnetization of said second ferromagnetic film.
5. A magnetic head according to claim 1, wherein the magnetization
direction of said first ferromagnetic film and said third
ferromagnetic film is prescribed to be in the same direction.
6. A magnetic head according to claim 1, wherein the magnetization
direction of said first ferromagnetic film and said third
ferromagnetic film is prescribed by antiferromagnetic films or hard
magnetic films which are respectively in contact with both said
first ferromagnetic film and said third ferromagnetic film.
7. A magnetic head according to claim 1 in which a film thickness
of the second ferromagnetic film is smaller than a film thickness
of the first ferromagnetic film.
8. A magnetic head comprising: a first spin valve element; a second
spin valve element; and a non-magnetic spacer layer formed between
the first spin valve element and the second spin valve element; the
first spin valve element including: a first antiferromagnetic film
a first ferromagnetic film; a first non-magnetic film made of Ru; a
second ferromagnetic film; a second non-magnetic film of which the
magnetization direction can be rotated in respect to an external
magnetic field; and a first soft magnetic film; the second spin
valve element including: a second antiferromagnetic film; a third
ferromagnetic film; a third non-magnetic film; and a second soft
magnetic film of which the magnetization direction can be rotated
in respect to an external magnetic field; wherein: the
magnetization direction of the second ferromagnetic film and the
magnetization direction of the third ferromagnetic film are in an
antiparallel state; and the first soft magnetic film and the second
soft magnetic film are arranged to be symmetrical with respect to
the non-magnetic spacer layer.
9. A magnetic head according to claim 8, wherein said first
non-magnetic medium layer consists of any one of metal layers
selected from a group of Ru, Rh, Ir, Cr, and Cu or consists of an
alloy containing some of these metals.
10. A magnetic head according to claim 8, wherein said second
non-magnetic film and said third non-magnetic film comprise a Cu
layer.
11. A magnetic head according to claim 8, wherein the product of
the film thickness and saturation magnetization of said first
ferromagnetic film is larger than the product of the film thickness
and saturation magnetization of said second ferromagnetic film.
12. A magnetic head according to claim 8, wherein the magnetization
direction of said first ferromagnetic film and said third
ferromagnetic film is prescribed to be in the same direction.
13. A magnetic head according to claim 8, wherein the magnetization
direction of said first ferromagnetic film and said third
ferromagnetic film is prescribed by antiferromagnetic films or hard
magnetic films which are respectively in contact with both said
first ferromagnetic film and said third ferromagnetic film.
14. A magnetic head according to claim 8 in which a film thickness
of the second ferromagnetic film is smaller than a film thickness
of the first ferromagnetic film.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a magnetic storage apparatus used
for computers and information processing apparatuses, and more
particularly relates to a magnetic head and a magnetic storage
apparatus suitable for a perpendicular magnetic recording medium
obtained realizing a high density recording.
[0003] 2. Description of the Prior Art
[0004] Information processing apparatus employs mainly
semiconductor memory and magnetic memory as their storage
apparatus. Semiconductor memory is used mainly for the internal
storage apparatus in view of access time, and magnetic memory is
used mainly for external storage apparatus in view of large
capacity and non-volatility.
[0005] Recently, magnetic disk and magnetic tape have been mainly
used as magnetic memory. A recording medium used for these magnetic
memory comprises an Al substrate or resin tape on which a magnetic
thin film is formed. To record magnetic information on the
recording medium, a functional component having electromagnetic
conversion function is used. To reproduce magnetic information, a
functional component which utilizes magnetoresistive phenomenon,
giant magnetoresistive phenomenon, or electromagnetic induction
phenomenon is used. The functional component is incorporated in an
input/output unit so-called a magnetic head.
[0006] A magnetic head and a recording medium are moved relatively,
and have a function to record magnetic information on the arbitrary
position of the medium and to reproduce electrically magnetic
information as required.
[0007] As shown in FIG. 2, a magnetic head comprises, for example,
a recording component 21 for recording magnetic information and a
reproducing component 22 for reproducing magnetic information.
[0008] The recording component 21 comprises a coil 26 and
magnetically coupled magnetic poles 27 and 28 located so that the
coil 26 is sandwiched therebetween.
[0009] The reproducing component 22 comprises a magnetoresistive
effect unit 23 and an electrode 29 for supplying a constant current
to the magnetoresistive effect unit 23 and for detecting resistance
change.
[0010] Between the recording component 21 and the reproducing
component 22, a magnetic shield layer 28 (served also as the write
pole) is provided. These functional components are formed on a
magnetic head body 30 through a primary layer.
[0011] The example shown in FIG. 2 utilizes electromagnetic
conversion function for recording and utilizes magnetoresistive
effect for reproducing. However, the reproduction of magnetic
information may be performed by detecting electromagnetic induction
current induced in a coil provided in a recording component. In
this case one component is served for both recording and
reproducing.
[0012] The performance of a storage apparatus depends on the
input/output operation speed and storage capacity, as a result,
short access time and large storage capacity are essential to
render the product competitive. Recently small sized storage
apparatus have been developed in response to the request for
compact information apparatus. To satisfy this request, development
of a magnetic memory device for recording and reproducing much
magnetic information in and from a single sheet of recording medium
is important.
[0013] To satisfy this request, it is required to increase the
recording density of a magnetic memory device. To increase the
recording density, it is required to miniaturize the size of domain
which is the source of magnetic information. It is required to
increase the frequency of recording current supplied to the coil 26
shown in FIG. 2 and to design the width W of recording magnetic
pole 27 narrow.
[0014] According to the examination of the inventors, a condition
that a recording pole width W of 2.5 .mu.m and a recording
frequency of about 90 MHz realized a recording density of 2
Gb/in.sup.2 class. However, it was found that more increased
density caused a problem and revealed the limitation of high
density recording.
[0015] Heretofore, magnetic films called as longitudinal media of
in-plane magnetization direction have been used as recording media.
In an in-plane medium, boundary between domains is mainly
magnetized, the magnetization is read out by detecting field
intensity. Because the magnetization is concentrated, a signal of
Gaussian shape (Lorentzian shape) pulse signal is outputted. Since
frequency band contained in a signal is narrow, it is less
susceptible to the deterioration of signal quality due to
neighboring signal. Therefore, signals are processed easily
thereafter.
[0016] However, thermal fluctuation of magnetization is inevitable
problem in development of high density recording using an in-plane
medium. The thermal fluctuation is due to thermal fluctuation of
magnetization in a recording medium, and the thermal fluctuation is
caused with increasing miniaturization of domain because the
demagnetizing effect of neighboring domain becomes remarkable and
magnetization direction becomes unstable.
[0017] According to experiments conducted by the inventors, it was
confirmed that domain could be erased due to thermal fluctuation
when density was increased as high as to about 400 kbPI (bits per
inch) in the circular direction and about 26 kTPI (tracks per inch)
in the radius direction.
[0018] The perpendicular magnetic recording is known as a
technology for preventing the problem. Because demagnetization of
neighboring domain functions so that fluctuation width of
magnetization due to thermal fluctuation is decreased, the domain
erasing phenomenon due to thermal fluctuation is less susceptible.
Therefore, the perpendicular magnetic recording is expected to be
the high density recording technology of the future.
[0019] However, because magnetic charges are distributed on the
medium surface in the perpendicular magnetic recording, if
magnetization is reproduced using a reproducer used for detecting
field intensity of a conventional longitudinal medium as shown in
FIG. 2, square wave (dipulse) is detected depending on domain
width. Such square wave requires complex signal processing because
of wide band. Such complex signal processing requires use of a
complex electric circuit. Therefore, it is difficult to realize an
inexpensive and high speed apparatus, and as a result, this problem
is one of the reasons of slow commercialization of the
perpendicular magnetic recording.
SUMMARY OF THE INVENTION
[0020] The above-mentioned problem will be solved if output signals
obtained from perpendicular media are of Gaussian shape similarly
to conventional longitudinal media.
[0021] Accordingly, it is the object of the present invention to
provide a magnetic head and a magnetic recording apparatus using
the magnetic head having a novel reproducing means which is capable
of outputting reproducing signal obtained from a perpendicular
magnetic medium as Gaussian shape pulse signal. The present
invention can realizes high speed and high density magnetic
recording apparatus which utilizes perpendicular magnetic recording
method.
[0022] In order to realize the above-mentioned object, the magnetic
head and the magnetic recording apparatus using the magnetic head
of the present invention use means described hereinafter.
[0023] The first means uses a perpendicular magnetization film
having an easy magnetization axis perpendicular to the direction of
the film surface, and the first means is provided with at least a
magnetic head having a function for recording and reproducing
information. Particularly in the magnetic head, a reproducing means
for having reproducing function of information is provided with
piled up two spin valve elements with a pinned layers having
magnetization direction difference of about 180 degrees, and
recorded information is reproduced from the perpendicular
magnetization film.
[0024] In detail, the object of the present invention is
accomplished by providing a magnetic recording apparatus provided
with a perpendicular magnetic recording medium having an easy
magnetization axis in the direction perpendicular to the
longitudinal surface, and a magnetic head having both recording and
reproducing function of information, wherein the magnetic head is
structured with a reproducing means comprising piled two (the first
and second) spin valve elements having at least a magnetoresistive
elements for performing reproducing function, and the magnetization
direction of pinned layers which are a components of each spin
valve element is different by about 180 degrees each other.
[0025] Both ends of two (first and second) spin valve elements
respectively provided with a magnetoresistive element is connected
commonly and an electrode is provided to each terminal, and
operation of read out (reproducing) means is performed by
connecting a constant voltage power source or constant current
power source to an electrode.
[0026] Preferably pinned layers of the piled two spin valve
elements comprises respectively an antiferromagnetic film, and a
blocking temperature difference of the respective antiferromagnetic
films is prescribed to be 20.degree. C. or larger. The blocking
temperature will be described hereinafter.
[0027] Alternatively, pinned layers of the piled two spin valve
element comprise a high coercive force film, and a coercive force
difference of the respective high coercive force films is
prescribed to be 100 Oe or lager.
[0028] A current terminal of the first spin valve element and a
current terminal of the second spin valve element are connected
commonly, and an electrode is provided on the common point. Thereby
two elements function as a single device.
[0029] Alternatively, the first spin valve element and the second
spin valve element are maintained electrically insulated, connected
so that output from the elements is in differential mode, and
supplied with a current.
[0030] In the above-mentioned case, a dual spin valve element
having the first spin valve element and the second spin valve
element provided with a single oxide antiferromagnetic film
inserted therebetween is structured.
[0031] The above-mentioned reproducing means is incorporated in a
magnetic head slider, and provided partially on an air bearing
surface at least near a perpendicular magnetic recording
medium.
[0032] In the above-mentioned reproducing means, the respective
spin valve elements are piled up closely, and a soft magnetic
pattern is provided between these spin valve elements on the side
distant from the air bearing surface. The soft magnetic pattern
forms a magnetic circuit from the first spin valve element to the
second spin valve element.
[0033] The second means to accomplish the above-mentioned object is
a magnetic recording apparatus comprising a perpendicular magnetic
recording medium having an easy magnetization axis in the direction
perpendicular to the film surface and a magnetic head having both
functions for recording and reproducing information. The
reproducing function of the magnetic head is given by a reproducing
means provided with the first spin valve element and the second
spin valve element piled up with interposition of a spacer film
which spin valve elements at least comprise a magnetoresistive
element, the first spin valve element comprises the first
ferromagnetic film, the first non-magnetic medium layer, the second
ferromagnetic film, the second non-magnetic film, and third
ferromagnetic film placed one on another in this order or in
inverse order, and functions thereby so that the first
ferromagnetic film and the second ferromagnetic film exert exchange
interaction each other so as to direct the magnetization direction
of the respective ferromagnetic films in inverse direction, and the
difference in magnetization direction between the second
ferromagnetic layer and the third ferromagnetic layer generates
magnetoresistive effect. The second spin valve element comprises
the fourth ferromagnetic film, the third non-magnetic medium layer,
and fifth ferromagnetic film placed one on another in this order or
in inverse order, and functions thereby so that the difference in
magnetization direction between the fourth ferromagnetic film and
the fifth ferromagnetic film generates magnetoresistive effect.
[0034] Both ends of two (first and second) spin valve elements
respectively provided with a magnetoresistive element is connected
commonly and an electrode is provided to each common point, and
operation of read out (reproducing) means is performed by
connecting a constant voltage power source or constant current
power source to an electrode.
[0035] In the structure of the spin valve element, the first
non-magnetic medium layer comprises a layer with a thickness of 1.5
nm or thinner consisting of any one of metal layers selected from a
group of Ru, Rh, Ir, Cr, and Cu or consisting of an alloy
containing some of these metals. The first non-magnetic medium
layer is sandwiched between ferromagnetic layers to generate strong
antiferromagnetic exchange interaction between these ferromagnetic
layers. As a result, the magnetization direction of the first
ferromagnetic layer and the magnetization direction of the second
ferromagnetic layer are always in antiparallel relation each
other.
[0036] The above-mentioned second non-magnetic medium and third
non-magnetic medium layer comprise a Cu layer.
[0037] The product of the film thickness and saturation
magnetization of the first ferromagnetic film is prescribed to be
larger than the product of the film thickness and saturation
magnetization of the second ferromagnetic film.
[0038] Further, a spacer film for separating the first spin valve
element from the second spin valve element is sandwiched between
the third ferromagnetic film and the fourth ferromagnetic film, and
the third ferromagnetic film and the fourth ferromagnetic film are
both comprise a soft magnetic film.
[0039] The magnetization of the first ferromagnetic film and the
fifth ferromagnetic film are prescribed to be in the same
direction.
[0040] The above-mentioned first ferromagnetic film and the fifth
ferromagnetic film are structured so that the magnetization
direction is specified by the antiferromagnetic film or hard
magnetic film which is in contact with these ferromagnetic films
respectively.
[0041] The third means to accomplish the above-mentioned object has
a structure in which, for example, the first spin valve element
having an Ru film provided between the first ferromagnetic film and
the second ferromagnetic film, and having a Cu film provided
between the second ferromagnetic film and the third ferromagnetic
film, and the second spin valve element having a Cu film provided
between the fourth ferromagnetic film and the fifth ferromagnetic
film and having an Ru film provided between the fifth ferromagnetic
film and the sixth ferromagnetic film are provided with
interposition of a desired spacer film adjacently, the reproducing
function component having the above-mentioned structure is used for
reproducing information.
[0042] In detail, the third means is a magnetic recording apparatus
provided with a perpendicular magnetic recording medium having an
easy magnetization axis perpendicular to the film surface direction
and a magnetic head having both functions for recording and
reproducing information. The reproducing function of the magnetic
head is given by a reproducing means provided with the first spin
valve element and the second spin valve element piled up with
interposition of a spacer film which spin valve elements at least
comprise a magnetoresistive element. The first spin valve element
has the first nonmagnetic medium layer between the first
ferromagnetic film and the second ferromagnetic film, and has the
second non-magnetic medium layer between the second ferromagnetic
film and the third ferromagnetic film, and the second spin valve
element has the third non-magnetic medium layer between the fourth
ferromagnetic film and the fifth ferromagnetic film, and has the
fourth non-magnetic medium layer between the firth ferromagnetic
film and the sixth ferromagnetic film.
[0043] An electrode is provided respectively on the both ends of
the two spin valve elements, and operation of read out
(reproducing) means is performed by connecting a constant voltage
power source or constant current power source to an electrode.
[0044] Preferable structure is described herein under. The first
non-magnetic medium layer and the fourth non-magnetic medium layer
respectively comprise a layer consisting of any one of metal layers
selected from a group of Ru, Rh, Ir, Cr, and Cu or consisting of an
alloy containing some of these metals.
[0045] The above-mentioned second non-magnetic medium layer and
third non-magnetic medium layer comprise respectively a Cu
layer.
[0046] The film thickness of the first ferromagnetic film is
prescribed to be thicker than the film thickness of the
ferromagnetic film, and the film thickness of the fifth
ferromagnetic film is prescribed to be thicker than the film
thickness of the sixth ferromagnetic film.
[0047] A spacer film for separating the first spin valve element
from the second spin valve element is provided between the third
ferromagnetic film and the fourth ferromagnetic film, and the third
ferromagnetic film and the fourth ferromagnetic film respectively
comprise a soft magnetic film.
[0048] The magnetization direction of the first ferromagnetic film
and the fifth ferromagnetic film are respectively structured so as
to be directed in the same direction.
[0049] Further, the magnetization direction of the first
ferromagnetic film and sixth ferromagnetic film is specified
respectively by an antiferromagnetic film or hard magnetic film
which are respectively in contact with these ferromagnetic
films.
BRIEF DESCRIPTION OF THE DRAWING
[0050] FIG. 1A is a perspective view for illustrating the structure
of a reproducing means of one example of the present invention.
[0051] FIG. 1B is a sectional view of the reproducing means taken
along the line .alpha. in FIG. 1A.
[0052] FIG. 1C is a sectional view of the reproducing means taken
along the line .beta. in FIG. 1A.
[0053] FIG. 1D is a sectional view for illustrating piling up of
spin valve elements 33 and 34 taken along the line .beta. in FIG.
1A.
[0054] FIG. 2 is a perspective view for illustrating a reproducing
component 21 and recording component 22 of a conventional magnetic
head.
[0055] FIG. 3 is a plan view of a magnetic recording apparatus
provided with a reproducing means to which the present invention is
applied as a reproducing component of a magnetic head.
[0056] FIGS. 4A and 4B are diagrams for describing the principle of
the head using dual MR as a reproducing means.
[0057] FIG. 5A is a perspective view for illustrating the structure
of a reproducing means of the second example of the present
invention.
[0058] FIG. 5B is a sectional view for illustrating piling up of
piled up two spin valve elements 33 and 34 in FIG. 5A.
[0059] FIG. 5C is a diagram of a circuit for processing signal
outputted from piled up two spin valve elements 33 and 34 in FIG.
5A.
[0060] FIG. 6A, FIG. 6B, and FIG. 6C are schematic diagrams for
describing operational principle of the present invention
comprising piled up two spin valve elements 33 and 34.
[0061] FIG. 7A and FIG. 7B are diagrams for describing operational
principle of a reproducing means of one example of the present
invention.
[0062] FIG. 8 is a diagram for describing operational principle of
a reproducing means of another example of the present
invention.
[0063] FIG. 9 is a sectional view of a spin valve element which is
a component of the reproducing component of another example of the
present invention.
[0064] FIG. 10A and FIG. 10B are diagrams for describing
magnetization of two spin valve elements 33 and 34.
[0065] FIG. 11A1 and FIG. 11A2 are diagrams for describing
principle for changing pinned layer magnetization antiparallel of
the spin valve element 34.
[0066] FIG. 11B1 and FIG. 11B2 are diagrams for describing
principle for changing pinned layer magnetization antiparallel of
the spin valve element 33.
[0067] FIG. 12A and FIG. 12B are diagrams for describing
operational principle of a reproducing component of the present
invention.
[0068] FIG. 13 is a sectional view for illustrating a reproducing
means comprising a piled up two spin valve elements of another
example of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Example
[0069] A typical structure of a reproducing component of a magnetic
head to which a magnetic recording apparatus of the present
invention will be described hereinafter with reference to FIG. 1A
to FIG. 1D.
[0070] FIG. 1A is a schematic diagram of the reproducing component
(corresponds to the reproducing component shown in FIG. 2). The
reproducing component comprises a magnetoresistive element 32 and
electrodes 31. In the present invention, a giant magnetoresistive
element or conventional magnetoresistive element may be used as the
magnetoresistive element 32. An example in which a giant
magnetoresistive element is used is described in this example.
[0071] FIG. 1B shows a sectional structure taken along the line
.alpha. in FIG. 1A, and FIG. 1C shows a sectional structure taken
along the line .beta. in FIG. 1A. As shown in FIG. 1B and FIG. 1C,
the first giant magnetoresistive element 33 and the second giant
magnetoresistive element 34 are piled up, and a non-magnetic film
is provided between the giant magnetoresistive elements 33 and 34.
Magnetic patterns 35 having high coercive force are provided on
both ends of the giant magnetoresistive elements 33 and 34 to
change the soft magnetic layer which is a component of the giant
magnetoresistive element to a single domain and to arrange
magnetization in the same direction.
[0072] The magnetization direction of the magnetic patterns 35 is
in parallel to the line .alpha. like the conventional longitudinal
medium. The electrodes 31 are located on the magnetic patterns 35,
and structured so as to supply a current to two giant
magnetoresistive elements 33 and 34 in the same direction.
[0073] In the structure described hereinbefore, the structure is
novel in that two functional thin films 33 and 34 corresponding to
giant magnetoresistive elements are piled up with interposition of
the non-magnetic film 36 and in that common electrodes 31 are
connected to these two functional thin films.
[0074] The electric resistance of each functional thin film changes
depending on the field intensity (perpendicular field component;
parallel field component to the line .beta. shown in FIG. 1A) at
the position where the functional thin film is located. The change
is detected as the change of the voltage between both ends by
supplying a constant current to the functional thin film.
Alternatively, the change can be detected as the change of the
current by supplying a constant voltage.
[0075] By using functional thin films located at positions distant
spatially each other, the field intensity at the positions distant
spatially each other can be measured simultaneously. Therefore, by
detecting the field intensity difference as an output difference,
the field gradient between the positions distant spatially each
other can be measured.
[0076] First, to detect the field intensity difference at the
positions distant spatially each other, two giant magnetoresistive
elements are structured to have a spin valve element structure in
this example. The detailed structure is described with reference to
FIG. 1D.
[0077] An under layer film (Hf: 5 nm) 41 is deposited, and
successively a soft magnetic film (free layer: NiFe: 6 nm) 42, a
non-magnetic film (Cu: 3 nm) 43, a pinned layer (pinned layer:
NiFe: 3 nm) 44, and an antiferromagnetic film (Fe--Mn: 10 nm) are
deposited, and these films constitute the first spin valve element
(giant magnetoresistive element or functional thin film in a
broader sense of the term) 34.
[0078] Similarly, the second spin valve element 33 is also formed
by depositing a under layer film (Hf: 5 nm) 46, a soft magnetic
film (free layer: NiFe: 6 nm) 47, a non-magnetic layer (Cu: 3 nm)
48, a pinned layer (pinned layer: NiFe: 3 nm) 49, an anti-magnetic
film (Fe--Mn: 10 nm) 50, and a protection layer (Hf: 5 nm) 51
successively.
[0079] To detect the field intensity difference using the
above-mentioned structure, the magnetization direction of the
pinned layer 44 which is a component of the first spin valve
element 34 is differentiated angularly from the magnetization
direction of the pinned layer 49 which is a component of the second
spin valve element 33 by 180 degrees. To realize the difference,
the blocking temperature of the antiferromagnetic films 45 and 50
which are components of two spin valve elements is differentiated
each other by 20.degree. C. or larger.
[0080] The magnetization direction of the pinned layers 44 and 49
can be prescribed to be parallel or antiparallel with respect to a
prescribed axis (usually, in the direction parallel to the line
.beta. shown in FIG. 1A) by exchange interaction from the
antiferromagnetic films 45 and 50. The parallel magnetization
direction or antiparallel magnetization direction can be prescribed
by applying an external field. The exchange interaction is
dependent on the temperature, and demagnetized above a certain
temperature. The temperature is called as blocking temperature.
[0081] As described herein above, the magnetization of a pinned
layer can not be prescribed above the blocking temperature.
Therefore, if the blocking temperature of the antiferromagnetic
films 45 and 50 which are components of each spin valve element is
different in the laminated spin valve elements 33 and 34, the
magnetization of a pinned layer can be prescribed by controlling
the temperature when an external field is applied.
[0082] The blocking temperature is different depending on
antiferromagnetic material such as NiFe, NiMn, IrMn, and NiO,
further, the blocking temperature of the same material is different
depending on composition and deposition condition. The difference
is controllable and it is easy to differentiate the blocking
temperature by 20.degree. C. or larger. The blocking temperature
difference of 20.degree. C. or larger allows easy pinned layer
magnetization inversion of 180 degrees, that is, there is no
probelm in magnetize operation.
[0083] From the reason described herein above, it is understandable
that the magnetization direction of the pinned layer 44 which is a
component of the first spin valve element 34 and the pinned layer
49 which is a component of the second spin valve element 33 is
changed by about 180 degrees each other (to antiparallel
relation).
[0084] Next, the reason why the field intensity difference can be
detected by changing the magnetization direction of the pinned
layer 44 of the first spin valve element 34 and the pinned layer 49
of the second spin valve element 33 by about 180 degrees (to
antiparallel relation) is described.
[0085] FIG. 6A shows the magnetization state of a spin valve
element (giant magnetoresistive element in a broader sense). The
magnetization direction of the pinned layer 67 is antiparallel to
Y-axis (perpendicular field direction). The medium layer 66
consists of a non-magnetic material (Cu). The soft magnetic layer
(free layer) 65 having magnetization state parallel to X-axis is
located on the medium layer 66. When a field (perpendicular field
component: perpendicular to the plane of a recording medium) 68 is
applied to this layer, the magnetization 91 is turned to .alpha.
direction or .beta. direction depending on the direction of the
field. If the magnetization 91 turns in .alpha. direction, then it
is oriented toward the direction parallel to the magnetization
direction of the pinned layer 67. On the other hand, if the
magnetization 91 turns in .beta. direction, then it is oriented
toward the direction antiparallel to the magnetization of the
pinned layer 67. Based on the principle of the spin valve element,
the parallel state gives a low electrical resistance and the
antiparallel state gives a high electrical resistance.
[0086] Next, the sensitivity to a field gradient in the structure
simply comprising two spin valve elements piled up one above the
other as described herein above is examined.
[0087] As shown in FIG. 6B, two spin valve elements having a medium
layer 66-1 and medium layer 66-2 respectively are piled up one
above the other (elements are shown schematically apart each other
for the purpose of description in the drawing), and it is assumed
that a field 69 is applied to the first element and a field 70
directing to the opposite direction is applied to the second
element. As shown in the drawing, the magnetization of the soft
magnetic layer 65-1 turns in .beta. direction, and on the other
hand, the magnetization of the soft magnetic layer 65-2 turns in
.alpha. direction. The magnetization direction of the soft magnetic
layer 65-1 is antiparallel to the magnetization direction of the
pinned layer 67-1, and on other hand, the magnetization direction
of the soft magnetic layer 65-2 is parallel to the magnetization
direction of the pinned layer 67-2. Mere difference in polarity
between the external field 69 and 70 only results in the difference
in resistance between the elements, and the add resistance is not
changed (precisely to say, the add resistance changes slightly due
to quality dispersion of the element). In other words, the
structure shown in FIG. 6B is not sensitive to the field
gradient.
[0088] However, as shown in FIG. 6C, in the case of antiparallel
magnetization direction of the pinned layer 67-1 and pinned layer
67-2, the field 69 is applied to the first element and an opposite
field 70 is applied to the second element, then magnetization turns
as described herein above, and thereby both becomes antiparallel
(high resistance) to the magnetization direction of the pinned
layers 67-1 and 67-2 respectively. As a result, the add resistance
of two elements increases. On the other hand, in the case that the
external field 69 and the external field 70 are both oppositely
oriented, because the magnetization of the soft magnetic layer
turns in the opposite direction, both resistance decreases.
[0089] However, if the field 69 and field 70 are both parallel,
because the magnetization of the soft magnetic layers 65-1 and 65-2
both turns in the same direction, the magnetization direction of
the soft magnetic layers 65-1 and 65-2 is antiparallel and parallel
to the magnetization direction of the pinned layers 67-1 and 67-2
respectively. As a result, add resistance does not change. As
described herein above, by prescribing the direction of the pinned
layer magnetization of the first element and of the pinned layer
magnetization of the second element in antiparallel each other, the
spin valve element structure is rendered sensitive so that the
resistance is changed only when fields of different opposite
polarity are applied to two elements.
[0090] When a field gradient is applied between two spin valve
elements, a situation is formed, and this situation is the same as
that described herein above, namely, the situation formed when
different external fields are applied to two elements. The
difference causes a change in add resistance of two elements based
on the reason described herein above. The change is detected as the
change in current or voltage, that is obvious from the
above-mentioned reason.
[0091] This example is featured by antiparallel (about 180 degrees)
magnetization direction of the pinned layers 44 and 49 as shown in
FIG. 1D.
[0092] Alternatively to specify the magnetization direction of
these pinned layers, a method in which exchange coupling between a
high coercive force film such as .alpha.-Fe.sub.2 O.sub.3 film or
CoPt film and ferromagnetic film is used is known. In this case,
high coercive force films are deposited instead of the
antiferromagnetic films 45 and 50 (piled up at the same
position).
[0093] In the present invention, because two spin valve elements
are piled up, elements having a difference in corrosive force
between these elements of 100 Oe or larger are used. Because of the
difference in coercive force, the magnetization direction can be
prescribed by reducing successively magnetization field. Thereby,
the magnetization direction of a pinned layer is prescribed
arbitrarily (in the present invention, in antiparallel). The larger
the difference in coercive force is, the easier the magnetization
is, however, the difference of 100 oe or higher is sufficient for
practical application. It is well known that the difference in
coercive force is controlled by controlling material, film
composition, deposition temperature, and deposition velocity. The
above-mentioned operations are utilized to prescribe the
magnetization direction of pinned layera to be in antiparallel, and
applied to the present invention.
[0094] A field gradient detection means comprising two functional
thin films (spin valve elements 33 and 34) shown in the FIG. 1D is
incorporated in a magnetic head slider 2 which is similar to a
conventional magnetic head slider as shown in FIG. 3. The magnetic
head slider 2 is provided with a recording means according to a
prescribed manner. A perpendicular magnetic recording medium having
the axis of easy magnetization in the perpendicular direction to
the film plane is used as the recording medium 11. The magnetic
head slider 2 is supported by a suspension 7 and arm 4. A rotary
actuator 3 is used for positioning the magnetic head slider 2 and
recording medium. Other components such as a motor for rotating the
recording medium, a circuit board for processing electric signals,
and an electric circuit for controlling the whole apparatus are
used to complete the recording apparatus though they are not shown
in the drawing.
[0095] By applying the field gradient sensing system which is the
main component of the reproducing apparatus of this invention, the
output signal is rendered Gaussian shaped regardless of using a
perpendicular medium as a recording medium. Hence, the same signal
processing circuit as used in a reproducing apparatus which uses a
conventional recording medium having a longitudinal magnetization
film can be used. The signal processing circuit is featured in that
the circuit scale is small because of reduced number of signal
detection points and the circuit is excellent in high speed
capacity. Therefore, the increased recording density does not cause
any process time loss for processing signals.
[0096] The above-mentioned effect is obtained only by the present
invention and is realized by applying the field gradient detection
means provided with piled up two functional thin films (spin valve
elements 33 and 34) shown in FIG. 1D to the reproducing means for
reproducing magnetic information generated from a perpendicular
magnetization film.
[0097] To describe more clearly this point, the present invention
is described with reference to FIG. 7A and FIG. 7B.
[0098] FIG. 7A is a sectional view (cross section in the plane
parallel to the line .beta. in FIG. 1A) of a field gradient
detection means provided with two functional thin films 33 and 34
and a perpendicular magnetization film. In the perpendicular
magnetization film 11, the magnetic state turns from an upward
magnetic state 81 to a downward magnetic state 82 at the position
where information "1"is located, and the information is detected
based on the existence of a transition 80.
[0099] It is assumed that the first functional thin film 33 and the
second functional thin film 34 are positioned just above the
transition 80 of the medium. Magnetic fluxes are generated from
each domain in the arrow direction shown in the drawing, and these
magnetic fluxes penetrate into two functional thin films (in
detail, soft magnetic layers which are components of spin valve
elements).
[0100] Because of antiparallel magnetization state on the right vs.
left side separated at the boundary of transition 80, two fields
which act on two functional thin film are antiparallel. In other
words, a difference of the field is caused between two functional
thin films. The difference causes a change in add resistance of two
functional thin films because of the reason described herein above,
and the change is detected as an electric signal. Angular
directional turning of the magnetizations 81 and 82 results in
directional turning of magnetic flux which acts on two functional
thin films. This turning causes resistance change in reverse to the
above-mentioned manner (increase or decrease).
[0101] However, on a place where there is no transition just under
the first functional thin film 34 and the second functional thin
film 33 as shown in FIG. 7B, equal and weak magnetic fluxes (stray
field decreases due to demagnetization from domain itself)
penetrate to two functional thin films, no electric signal is
therefore generated.
[0102] As described herein above, only when a difference of the
field from a magnetic recording medium namely field gradient is
given, electric resistance of two functional thin films changes.
Because the change is differently incremental resistance or
decremental resistance depending on the magnetic state of polarity
of transition, Lorentzian pulse electric signal is obtained. Based
on this feature, it is possible to process signals using the same
signal processing as used conventionally (longitudinal
magnetization film) regardless of using of a perpendicular
magnetization film.
[0103] The above-mentioned example involves the generally used
structure of a spin valve element. However, the present invention
is also realized by using other spin valve element structure.
Second Example
[0104] Dual MR head described in THEORY OF MAGNETIC RECORDING by H.
NEAL BERTRAM on pages from 194 to 199 has been known as another
structure for detecting magnetic gradient generated by
perpendicular field. In this structure, as shown in FIG. 4A and
FIG. 4B, two magnetoresistive elements 61 and 63 are piled up with
interposition of an insulator layer or a high resistance film 62,
the fields generated by the current magnetize the magnetoresistive
elements asymmetrically. The asymmetrical magnetization is
determined by current intensity, element width, and distance
between magnetoresistive elements, and easily estimated based on
the soft adjustment layer (SAL) magnetoresistive sensor theory.
[0105] Though the above-mentioned structure is very simple, the
structure is disadvantageous in that sensitivity is low because the
functional thin film functions based on magnetoresistive effect.
Therefore, in the recording density range exceeding 10
Gb/in.sup.2where the perpendicular magnetization film is required,
the reproducing output is insufficient. Though magnetization
asymmetry causes no problem of symmetry property of amplitude (no
difference between plus signal and minus signal), the magnetization
asymmetry causes the change in symmetry of pulse on the time axis.
This phenomenon is not described in the above-mentioned disclosed
art. This problem of symmetry of pulse on the time axis is due to
the property of magnetoresistive element that the sensitivity of
two magnetoresistive elements change reversely (high and low)
depending on the magnetization asymmetry. This phenomenon results
in reproduction of a pulse having a wide skirt when magnetic
information is positioned on the side of magnetoresistive element
of higher sensitivity, and on the other hand, results in
reproduction of a pulse having a narrow skirt when magnetic
information is positioned reversely.
[0106] The interference between neighboring signals becomes
remarkable with increasing high density recording. When, if a
signal has nonlinear distortion, following signal processing can
not be performed. To avoid this trouble, two magnetoresistive
elements having the same sensitivity may be used, however, because
of inevitable some allowance of sensitivity in manufacturing and
accuracy of supplied current (including control of external factors
such as temperature), such factors cause the problem.
[0107] Because spin valve elements are used in the present
invention, the present invention is applied to dual MR head without
any problem. Because magnetization of a pinned layer is prescribed
in one direction by a antiferromagnetic film in the spin valve
structure, the problem of asymmetry is not involved. Such excellent
structure can not be derived from the above-mentioned conventional
art.
Third Example
[0108] Another example for realizing excellent reproducing function
from a perpendicular magnetization film using two spin valve
elements is described hereinafter. In this example, the first spin
valve element 34 and the second spin valve element 33 are
maintained in electric insulated condition. As shown in FIG. 5A,
electrodes 71 and 73 and 72 and 74 are connected to the respective
spin valve elements. These two pairs of electrodes are electrically
insulated.
[0109] To maintain two spin valve elements in electrically
insulated condition, an antiferromagnetic oxide film 52 is inserted
between two spin valve elements 33 and 34 as shown in the cross
sectional structure of FIG. 5B. NiFe alloy films 44 and 49 are
deposited on the top and bottom surface of the antiferromagnetic
oxide film 52, which is served as a pinned layer. On the outside
surface, Cu medium layers with a thickness of 3 nm (non-magnetic
layer) 43 and 48, and further NiFe alloy films with a thickness of
3 nm 42 and 47 are deposited. The NiFe alloy films 42 and 47 are
soft magnetic films and served as a free layer of a spin valve
element. To improve the function as a free layer, Hf films 41 and
46 are deposited additionally on the outside surface. The Hf film
is served also as a protection film.
[0110] As described herein above, each electrode may be insulated
with an antiferromagnetic oxide film 52 to maintain the first spin
valve element and the second spin valve element in electrically
insulated condition. In detail, antiferromagnetic oxide films 52
are provided between the electrodes 71 and 72 and between the
electrodes 73 and 74 to electrically insulate. In this case, the
process is simplified. By the way, in the above-mentioned
structure, because the magnetization of pinned layers 44 and 49 are
specified by free layers 42 and 47 consisting of common material
(NiFe alloy film), it is impossible to prescribe the magnetization
direction of the first spin valve element 34 and the second spin
valve element 33 in antiparallel. To prevent the problem, the
electrodes are insulated.
[0111] Using such structure, it is possible to reproduce recorded
information from a perpendicular magnetization film by applying
so-called differential operation, in which output electrodes 72 and
74 and output electrodes 71 and 73 are connected to amplifier
circuits of different polarity as shown in the circuit diagram of
FIG. 5C and respective outputs are synthesized. Output is obtained
finally only when outputs of different polarity are detected from
two spin valve elements, this fact explains the reason. This state
is equivalent to the state shown in FIG. 7A and FIG. 7B, and based
on this reason, it is possible to reproduce recorded information
from a perpendicular magnetization film.
[0112] This example is featured in that the effect of thermal
fluctuation is removed by differential operation circuit because
thermal fluctuation affects the respective elements commonly if it
occurs. The feature allows this method to be applied to contact
recording which is likely to be involved in disturbance though the
number of electrodes increases.
[0113] Reproducing function is realized by a method in which any
one of the above-mentioned reproducing means is provided to a
magnetic head slider, and a part of which is provided at least on
the air bearing surface near the perpendicular magnetization
recording medium surface.
[0114] When, as shown in FIG. 8, the soft magnetic pattern 38 is
provided on a place near the first and second spin valve elements
33 and 34 and distant from the air bearing surface. By providing
the soft magnetic pattern, a magnetic circuit is formed between the
spin valve element 33 and the spin valve element 34. The magnetic
circuit is effective for inducing efficiently the magnetic flux
from the magnetization 81 and magnetization 82 in the recording
medium 11. If there is no magnetic pattern, the magnetic flux flows
mostly from the side where two spin valve elements are located in
parallel each other to the neighboring element. However, if a
magnetic circuit is formed on the side which is distant from the
medium surface, the magnetic flux flows toward the magnetic
circuit. As a result, the magnetic flux flows into more area of the
elements, and the output is obtained efficiently.
Fourth Example
[0115] In this example, to detect the field intensity difference at
the position distant spatially, two giant magnetoresistive elements
having the structure as described herein under are piled up. The
example is described with reference to a sectional view of FIG.
9.
[0116] First, a primary film (Hf: 5 nm) 41 is piled on a substrate,
and an antiferromagnetic film (Fe--Mn: 10 nm) 45, and a magnetic
film (first ferromagnetic film: NiFe alloy: 6 nm) 44 are piled up
successively, thereafter an Ru film 56 having a thickness of 0.7 nm
is deposited, and further a magnetic film (second ferromagnetic
film: NiFe alloy film: 3 nm) 57 is deposited.
[0117] On the film 57, a non-magnetic film (Cu: 3 nm) 43 is
deposited, and then a soft magnetic film (third ferromagnetic film:
NiFe alloy film: 6 nm) 42 which functions as a free layer is
deposited. These successively deposited films constitute a first
spin valve element (a giant magnetoresistive element or functional
thin film in a broader sense of the term) 34.
[0118] Next, for forming a second spin valve element 33, a soft
magnetic film (fourth ferromagnetic film: NiFe alloy film: 6 nm) 47
which functions as a free layer is deposited on a spacer layer 46,
and on it a non-magnetic film (Cu: 3 nm) 48, and a magnetic film
(fifth ferromagnetic film: NiFe alloy film: 3 nm) 49 which function
as a pinned layer is deposited. On it an antiferromagnetic film
(Fe--Mn: 10 nm) 53 and a protection layer (Hf: 5 nm) 51 are
deposited.
[0119] This example is featured in that after deposition of the
magnetic film (first ferromagnetic film: NiFe alloy film: 6 nm) 44,
the Ru film 56 with a thickness of 0.7 nm is deposited, and the
magnetic film (second ferromagnetic film: NiFe alloy film: 3 nm) 57
is deposited. This structure is described in Digests of INTERMAG
'96 AA-04 by V. S. Speriosu et al. In this literature, it is
described that the magnetization direction of ferromagnetic films
between which the Ru film is sandwiched is antiparallel, the
magnetization direction of the ferromagnetic film having a thicker
thickness (to say precisely, higher product of saturation
magnetization and film thickness) is coincident with the external
field. This structure is featured in that the coercive force of the
total magnetic films between which the Ru film is sandwiched is
increased, and the magnetostatic effect on the external is reduced.
Application of this structure to a free layer or a pinned layer of
a spin valve element is suggested based on these features.
[0120] In this example, this structure is applied to a pinned
layer, but the purpose of the present invention is different from
that described in the above-mentioned literature. In detail, in
this example, two elements are provided at the positions distant
spatially each other to measure field intensity simultaneously, and
the difference in the field intensity is detected as an output
difference to measure the field gradient. To realize this
mechanism, in this example, an element structure in which the
magnetization direction of pinned layers of piled up two spin valve
elements is antiparallel is disclosed. Further, to realize this
structure, the example described the structure in which the
property of an Ru film is utilized. To clarify the novelty, it is
important to understand the requirement of antiparallel
magnetization of pinned layers, this point was described in detail
in the description of the first example with reference to FIG. 6A
and FIG. 6C.
[0121] FIG. 10A and FIG. 10B are sectional views for describing the
magnetization direction of the magnetic film which is required to
realize the present invention. The magnetization direction of the
magnetic film (first ferromagnetic film) 44 of the first spin valve
element 34 shown in FIG. 10A is regarded as a reference, and the
magnetization direction is assumed to be left facing to the paper
plane, then it is required that the magnetization direction of the
second ferromagnetic film 57 is right. The magnetization direction
of the magnetic film (fifth ferromagnetic film) 49 of the second
spin valve element 33 shown in FIG. 10B is required to be left. The
soft magnetic films 42 and 47 which function as a free layer have
an inclination of 90 degrees with respect to the pinned layer
magnetization (it is realized by magnetizing the permanent magnet
35 shown in FIG. 1B and FIG. 1C) so that the magnetization
direction both turns in the same direction when an external field
is applied.
[0122] The magnetization structure of the above-mentioned magnetic
film (pinned layer) is realized by magnetization processing shown
respectively in FIG. 11A1 FIG. 11A2, FIG. 11B1, and FIG. 11B2. FIG.
11A1 shows the structure after film forming of the first spin valve
element 34. In this structure, the magnetization direction of
respective magnetic films is not yet prescribed. As shown in FIG.
11A2, heat treatment is carried out at a temperature around the
blocking temperature of the antiferromagnetic film 45 under
application of an external field 61.
[0123] Because magnetization of the first ferromagnetic layer 44
and the second ferromagnetic layer 57 is coupled strongly in
antiparallel, both layers 44 and 57 behave together as one magnetic
film layer under a normal condition. The ferromagnetic layer having
the higher product of the film thickness and saturation
magnetization is predominant to the external field 61 out of two
ferromagnetic layers, and the magnetization direction of the
predominant ferromagnetic layer is parallel to the external field
61. As a result, the magnetization direction of the layer having
the lower product of the film thickness and saturation
magnetization is directed opposite to the external field 61. In
this example, the magnetization of the first ferromagnetic layer 44
is directed in the direction of the external field 61 and the
magnetization of the second ferromagnetic layer 57 is directed in
the direction opposite to the external field 61. The magnetization
of the first magnetic film 44 is fixed in the direction of the
external field 61 due to exchange coupling on the interface of the
antiferromagnetic layer 45. This principle is the same as involved
in the conventional spin valve element.
[0124] In this example, because the magnetic film 44 is in contact
with the Ru 56 which causes antiferromagnetic coupling in extremely
thin film condition, the magnetization direction of the second
magnetic film 57 which is in contact with the reverse interface is
antiparallel with respect to the external field 61. This phenomenon
is described in the above-mentioned literature.
[0125] Similarly, application of the external field 61 to the
structure after film forming of the second spin valve element 33
shown in FIG. 11B1 results in the state shown in FIG. 11B2. This
state is easily understandable from the fact that the magnetization
of the fifth magnetic film 49 is fixed in the direction of the
external field 61 due to the effect of exchange coupling from the
antiferromagnetic layer 53.
[0126] In the structure shown in FIG. 11A2 and FIG. 11B2, the
spacer 46 is used commonly, on both sides of the spacer 46 the
third magnetic film 42 and fourth magnetic film 47 which function
as a free layer are located. These magnetic films can be turned
freely by an external field as described hereinbefore. These
magnetic films are located on the magnetic film 57 (second magnetic
film) and the magnetic film 49 (fifth magnetic film) which function
as a pinned layer with interposition of the Cu films 43 and 48.
Because the magnetization direction of the magnetic film 57 (second
magnetic film) and the magnetic film 49 (fifth magnetic film) is
antiparallel each other based on the above-mentioned principle, the
first spin valve element 34 and the second spin valve element 33
perform differential function.
[0127] For structuring the above-mentioned magnetization structure,
emphasis is placed on making the film thickness of the second
magnetic film 57 thin relatively to the film thickness of the first
magnetic film 44. By structuring the magnetic films as described
herein above, the magnetization direction of the first magnetic
film 44 is directed preferentially in parallel to the external
field direction 61 (in the macro view point, magnetized so that
magnetostatic energy is reduced), and the magnetization direction
of the second magnetic film 57 located on the side in contact with
the free layer 42 is directed in antiparallel to the external field
direction 61. The principle described herein above can be estimated
easily from the above-mentioned literature, but there is a problem
in application of this principle to the dual type element structure
of the present invention. In detail, the coercive force of the
pinned layer comprising the first magnetic film 44, Ru film 56, and
second magnetic film 57 is insufficient.
[0128] Inventors of the present invention are aware of a knowledge
from experiments that equalization of fixing force of the pinned
layer magnetization of two elements is essential to secure symmetry
of the output for using the dual type element structure.
[0129] For the purpose of secure symmetry, in the present
invention, the magnetization direction of the first magnetic film
44 and the fifth magnetic film 49 are fixed by the
antiferromagnetic films 45 and 53. The difference of output between
the first spin valve element and the second spin valve element is
eliminated. This novel art is not disclosed in the above-mentioned
known example, it is said that this art is a novel art peculiar to
the dual type element of the present invention.
[0130] This problem is solved also by using a ferromagnetic film
consisting of high coercive force material such as Co--Pt instead
of the antiferromagnetic films 45 and 53. In this case, the
magnetization direction of the ferromagnetic film (equivalent to 45
and 53) is prescribed to be in parallel (equal) to the external
field by performing magnetization processing as shown in FIG. 11A1
FIG. 11A2, FIG. 11B1, and FIG. 11B2. Also in this case, the
magnetization of the ferromagnetic film and the pinned layer is
exchange-coupled, and the magnetization direction is prescribed.
Therefore, the desired spin valve element structure is structured
like th above-mentioned structure. By providing an Ru film in the
spin valve element, the magnetization direction of the pinned layer
which is in contact with the non-magnetic Cu film is prescribed to
be in antiparallel to the magnetization field. Thereby, the same
function as that of the above-mentioned example can be
realized.
[0131] In the above-mentioned example, a NiFe alloy film is used as
the magnetic films 44 and 57, however alternatively a Co ally film
which is a magnetic film may be used for the present invention
without any problem. Similarly, Ta or oxide may be used for the
protection film 51 instead of Hf film without any problem in
application of the present invention.
[0132] Further, to enhance the function of the first and second
spin valve elements, an extremely thin film of Co r NiFe may be
provided on the interface facing to the Cu layer or Ru layer, this
method is applied to the present invention without any problem.
Therefore it is obvious that these examples are included in the
present invention.
[0133] The case that Ru is used for the first non-magnetic layer 56
is described in the above-mentioned examples, however
alternatively, any one metal selected from a group including Ir,
Rh, Cr, and Cu or any one alloy containing two or more alloy
materials which results in strong antiferromagnetic layer coupling
may be used instead of Ru, and it is confirmed that these materials
give the same effect as Ru.
[0134] A field gradient detection means comprising two functional
thin films described hereinbefore is incorporated into a
conventional magnetic head slider 2 shown in FIG. 3. In the
magnetic head slider 2, a recording means is provided in the usual
manner. A perpendicular magnetic recording medium having an axis of
easy magnetization in perpendicular direction to the film plane is
used as the recording medium 11. The magnetic head slider 2 is
supported by the suspension member 7 and arm 4. The magnetic head
slider 2 and the recording medium are positioned by the rotary
actuator 3. A recording apparatus of the present invention is
completed using other components such as a motor for rotating the
recording medium, circuit board for processing electric signal, and
electric circuit for controlling the whole apparatus, which are not
shown in the drawings. By applying the field gradient detection
means which is the main component of the present invention,
reproducing signal of Gaussian shape is obtained regardless of
using a perpendicular magnetic film medium as a recording medium.
As a result, the same signal processing circuit as used for signal
processing of a longitudinal magnetization film recording medium is
used successfully.
[0135] This signal processing circuit has a small number of signal
detection points and is a circuit of a small scale, and excellent
in high speed performance. Signal processing causes no processing
time loss regardless of increased recording density.
[0136] The above-mentioned effect can be obtained only by the
present invention, and the effect is realized by applying the field
gradient detection means comprising piled up two functional thin
films to a means for reproducing magnetic information generated
from a perpendicular magnetic film. To clarify this point, the
example is described in detail with reference to FIG. 12A and FIG.
12B. FIG. 12A shows a sectional view (sectional view along the
plane parallel to the line .beta. in FIG. 1) of the field gradient
detection means comprising piled up two functional thin films and
the perpendicular magnetic film. In the perpendicular magnetic film
11, the magnetization condition changes from upward magnetization
81 to downward magnetization 82 at the position where the
information "1" is located. Therefore information is read out based
on the existence of the transition 80.
[0137] It is assumed that the first functional thin film 65-1
(equivalent to the first spin valve element 34) and the second
functional thin film 65-2 (equivalent to the second spin valve
element 33) are positioned just above the transition 80 on the
perpendicular magnetization film, a magnetic flux is generated in
the direction as described in the drawing from each domain, and the
magnetic flux penetrates into two functional thin films (in detail,
the soft magnetic layer which is a component of a spin valve
element). Because the right and left magnetization states are
different and antiparallel with respect to the border of the
transition 80, fields acting on two functional thin films are
antiparallel each other. It is understandable that field difference
is generated between two functional thin films. As a result, add
resistance of two functional thin films changes based on the reason
described herein above, and the change is detected as an electric
signal. When the direction of the magnetization 81 and 82 is
reversed, then the direction of the magnetic flux is also reversed.
As a result, resistance change opposite to the above-mentioned case
occurs (increase or decrease of the resistance).
[0138] However, on a place where there is no transition just under
the first functional thin film 65-1 and the second functional thin
film 65-2 as shown in FIG. 12, an equal and weak magnetic flux
(stray field decreases due to demagnetization from domain itself)
penetrates into two functional thin films, and no electric signal
is generated.
[0139] As described herein above, the resistance changes only when
the field difference from a medium between two functional thin
films namely the field gradient is caused. Because the change
results in resistance increment or resistance decrement depending
on the magnetization state of a transition position, Lorentzian
pulse electric signal is obtained. Based on this feature, the same
signal processing as used for a conventional longitudinal
magnetization film is used successfully regardless of using a
perpendicular magnetization film.
Fifth Example
[0140] The above-mentioned examples provided with generally used
spin valve elements are described. However, other spin valve
element structures may be applied to realize the present invention.
For example, an element having a pinned layer of the second spin
valve element 33 shown in FIG. 13 comprising the fifth magnetic
film 49, the Ru film 54, and the sixth magnetic film 55 with the
magnetization direction fixed by the antiferromagnetic film 53 is
included in the scope of the present invention. In this example,
other basic element structure, magnetization structure, and
electrode structure is the same as the above-mentioned examples. In
this example, the structure of the pinned layer is the same as that
of the first spin valve element. Therefore the output of the first
spin valve element 34 and the second spin valve element 33 is
completely symmetrical, and excellent reproducing processing is
performed.
[0141] To apply the spin valve element which uses the two Ru films
54 and 56 to the present invention, it is required that the
magnetization direction of the second magnetic film 57 and the
magnetization direction of the fifth magnetic film 49 are
antiparallel each other. To realize the antiparallel magnetization
direction by applying an external field, it is required that the
product of the film thickness and saturation magnetization of the
first magnetic film 44 which is in contact with the
antiferromagnetic film 45 is larger than the product of the film
thickness and saturation magnetization of the second magnetic film
57, and also the product of the film thickness and saturation
magnetization of the sixth magnetic film 55 which is in contact
with the antiferromagnetic film 53 is smaller than the product of
the film thickness and saturation magnetization of the fifth
magnetic film.
[0142] A hard magnetic film (ferrimagnetism, forromagnetism) which
has the same magnetization direction as that of an external field
is used at the same position instead of the antiferromagnetic film
53 without any problem. Elimination of the ferromagnetic film does
not cause any problem to realize the present invention. Though this
example is a special case, this example also involves the same
principle to solve the problem on which the present invention
addresses, therefore this example should be included in the scope
of the present invention.
[0143] Any one of the above-mentioned reproducing means is provided
in a magnetic head slider, and a portion of the reproducing means
is located on the air bearing surface at least near a perpendicular
magnetic recording medium surface, and thus reproducing function is
realized.
[0144] According to the present invention described hereinbefore,
reproducing signal is Gaussian shaped regardless of using a
perpendicular magnetic film as a recording medium. Based on this
effect, the same signal processing circuit as used for reproducing
a longitudinal magnetization film recording medium is used
successfully. Because such signal processing circuit has the small
number of signal detection points, the circuit scale is small, and
the signal processing circuit is excellent in high speed
performance. As a result, there is no processing time loss in
signal processing regardless of increased recording density.
[0145] The above-mentioned effect can be obtained only by the
present invention, and realized by applying a detection means
comprising piled up two spin valve elements to a reproducing means
of magnetic information obtained from a perpendicular magnetization
film. Based on the effect described hereinabove, a high density
storage apparatus having a recording density of 10 Gb/in.sup.2 or
more using a perpendicular magnetization film is realized.
[0146] The reproducing head of this invention is effective also for
densification of longitudinal magnetization film recording. The
reason is described herein under. In the improvement of linear
density of a longitudinal magnetization film, the reproducing
resolution is specified by the distance of the shield in the case
of a conventional magnetoresistive reproducing head and spin valve
head. In other words, it is required that the distance of the
shield is narrow for high liner density. However, it is very
difficult for narrow distance of the shield that the multi-layered
complex structure such as a spin valve is located between shields
and the electric insulation between the shield and the spin valve
is maintained consistently. On the other hand, because a simple
spacer layer specifies the resolution and electric insulation is
not required in the method of the present invention, the high
linear density is realized easily.
* * * * *