United States Patent [19]
`Heim et al.
`
`l|ll|||||l|l|l|l|llllllllllIlllllllllllllll||l|llllllllllllllllllllllllllll
`5,465,185
`Nov. 7, 1995
`
`USOO5465185A
`[11] Patent Number:
`[45] Date of Patent:
`
`[54] MAGNETORESISTIVE SPIN VALVE SENSOR
`WITH IMPROVED PINNED
`FERROMAGNETIC LAYER AND MAGNETIC
`RECORDING SYSTEM USING THE SENSOR
`
`[75] Inventors: David E. Heim, Redwood City; Stuart
`S. P. Parkin, San Jose, both of Calif.
`
`[73] Assignee: International Business Machines
`Corporation, Armonk, NY.
`
`[21] Appl. No.: 139,477
`[22] Filed:
`Oct. 15, 1993
`
`[51] Int. Cl.6 ...................................................... .. G11B 5/39
`[52] US. Cl. ................... .. 360/113; 324/207.21; 324/252;
`338/32 R
`[58] Field of Search ........................ .. 360/113; 338/32 R,
`338/32 H; 324/252, 207.21
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`4,949,039
`
`8/1990 Grunberg .............................. .. 324/252
`
`5,134,533
`
`7/1992 Friedrich et a1. . . . . .
`
`. . . . .. 360/113
`
`5,159,513 10/1992 Dieny et a1. . . . . . . . . . .
`
`. . . . .. 360/113
`
`5,206,590
`5,287,238
`
`4/1993 Dieny et al. . . . . . . . . . .
`2/1994 Baumgart et al.
`
`4/1994 Cain et al. . . . . . . . . . . . .
`5,301,079
`4/1994 Saito et al. ...... ..
`5,304,975
`5,313,186 5/1994 Schuhl etal.
`
`. . . . .. 324/252
`.... .. 360/113
`
`. . . . .. 360/113
`338/32 R
`338/32R
`
`5,315,468
`5,341,261
`
`5/1994 Lin et a1. . . . . . . . . . .
`. . . . .. 360/113
`8/1994 Dieny et a1. .......................... .. 360/113
`
`OTHER PUBLICATIONS
`
`Binasch et al., “Enhanced Magnetoresistance in Layered
`Magnetic Structures with Antiferromagnetic Interlayer
`Exchange”, Physical Review B, vol. 39, No. 7, Mar. 1, 1989,
`pp. 4828-4830.
`Dieny et al., “Change in Conductance is the Fundamental
`Measure of Spin-Valve Magnetoresistance”, Applied Phsy
`ics Letters, vol. 61, No. 17, Oct. 26, 1992, pp. 2111-2113.
`Dieny, “Quantitative Interpretation of Giant Magnetoresis
`tance Properties of Perrnalloy-based Spin-Valve Struc
`tures”, Europhysics Letters, vol. 17, No. 3, Jan. 14, 1992, pp.
`261-267.
`
`Dieny, “Classical Theory of Giant Magnetoresistance in
`Spin-Valve Multilayers: Influence of Thickness, Number of
`Periods, Bulk and Interfacial Spin-dependent Scattering”,
`Journal of Physics: Condensed Matter, vol. 4, 1992, pp.
`8009-8020.
`Dieny et al., “Giant Magnetoresistance in Soft Ferromag~
`netic Multilayers”, Physical Review B, vol. 43, No. 1, Jan.
`1, 1991, pp. 1297-1300.
`Levy, “Giant Magnetoresistance in Magnetic Layered and
`Granular Materials”, Science, vol. 256, May 15, 1992, pp.
`972-973.
`Parkin et al., “Giant Magnetoresistance in Antiferromag
`netic Co/Cu Multilayers”, Applied Physics Letters, vol. 58,
`No. 23, Jun. 10, 1991, pp. 2710-2712.
`
`(List continued on next page.)
`
`Primary Examiner-—Stuart S. Levy
`Assistant Examiner—George J. Letscher
`Attorney, Agent, or Firm—Thomas R. Berthold
`
`[57]
`
`ABSTRACT
`
`A spin valve magnetoresistive (MR) sensor uses a multi?lm
`laminated pinned ferromagnetic layer in place of the con
`ventional single-layer pinned layer. The laminated pinned
`layer has at least two ferromagnetic ?lms separated by an
`antiferromagnetically coupling ?lm. By appropriate selec
`tion of the thickness of the antiferromagnetically coupling
`?lm, depending on the material combination selected ‘for the
`ferromagnetic and antiferromagnetically coupling ?lms, the
`ferromagnetic ?lms become antiferromagnetically coupled.
`In the preferred embodiment, the pinned layer is formed of
`two ?lms of nickel-iron (Ni—Fe) separated by a ruthenium
`(Ru) ?lm having a thickness less than approximately 10 A.
`Since the pinned ferromagnetic ?lms have their magnetic
`moments aligned antiparallel with one another, the two
`moments can be made to essentially cancel one another by
`making the two ferromagnetic ?lms of substantially the
`same thickness. As a result, there is essentially no dipole
`?eld to adversely aifect the free ferromagnetic layer, which
`improves the sensitivity of the sensor and allows higher
`recording density to be achieved in a magnetic recording
`data storage system.
`
`46 Claims, 6 Drawing Sheets
`
`CURRENT
`SOURCE
`
`82
`
`80
`67
`
`66
`
`72
`65
`
`63
`
`62
`
`TDK Corporation Exhibit 1012 Page 1
`
`

`
`5,465,185
`Page 2
`
`OTHER PUBLICATIONS
`Parkin et al., “Spin Engineering: Direct Determination of the
`Ruderman-Kittel-Kasuya-Yosida Far-?eld Range Function
`in Ruthenium”, Physical Review B, vol. 44, No. 13, Oct. 1,
`1991, pp. 7131-7134.
`Parkin et a1., “Oscillations in Exchange Coupling and Mag
`netoresistance in Metallic Superlattice Structures: Co/Ru,
`Co/Cr, and Fe/Cr”, Physical Review Letters, vol. 64, No. 19,
`May 7, 1990, pp. 2304-2307.
`Parkin et a1., “Oscillatory Magnetic Exchange Coupling
`Through Thin Copper Layers”, Physical Review Letters,
`vol. 66, No. 16, Apr. 22, 1991, pp. 2152-2155.
`
`Parkin, “Systematic Variation of the Strength and Oscilla
`tion Period of Indirect Magnetic Exchange Coupling
`through the 3d, 4d, and 5d Transition Metals”, Physical
`Review Letters, vol. 67, No. 25, Dec. 16, 1991, pp.
`3598-3601.
`Parkin, “Giant Magnetoresistance and Oscillatory Interlayer
`Exchange Coupling in Copper Based Multilaycrs”, Materi
`als Research Society Symposium Proceedings, vol. 231,
`1992-, pp. 211-216.
`Pennisi, “Magnetic Advantage: Magnetic Fields Make New
`Thin Films Better Conductors”, Science News, vol. 142,
`Aug. 29, 1992, pp. 140-142.
`
`TDK Corporation Exhibit 1012 Page 2
`
`

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`US. Patent
`
`Nov. 7, 1995
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`TDK Corporation Exhibit 1012 Page 4
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`

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`US. Patent
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`Nov. 7, 1995
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`TDK Corporation Exhibit 1012 Page 5
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`

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`US. Patent
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`Nov. 7, 1995 -
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`TDK Corporation Exhibit 1012 Page 7
`
`

`
`US. Patent
`
`Nov. 7, 1995
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`TDK Corporation Exhibit 1012 Page 8
`
`

`
`5,465,185 .
`
`1
`MAGNETORESISTIVE SPIN VALVE SENSOR
`WITH IMPROVED PINNED
`FERROMAGNETIC LAYER AND MAGNETIC
`RECORDING SYSTEM USING THE SENSOR
`
`TECHNICAL FIELD
`
`This invention relates generally to a magnetoresistive
`(MR) sensor based on the spin valve effect for sensing
`magnetic ?elds, and more particularly to such a sensor
`having an improved pinned ferromagnetic layer, and to
`magnetic recording systems which incorporate such sensors.
`
`10
`
`BACKGROUND OF THE INVENTION
`
`An MR sensor detects magnetic ?eld signals through the
`resistance changes of a read element, fabricated of a mag
`netic material, as a function of the strength and direction of
`magnetic ?ux being sensed by the read element. The con
`ventional MR sensor, such as that used in the IBM “Corsair”
`disk drive, operates on the basis of the anisotropic magne
`toresistive (AMR) effect in which a component of the read
`element resistance varies as the square of the cosine of the
`angle between the magnetization in the read element and the
`direction of sense current ?ow through the read element.
`Recorded data can be read from a magnetic medium because
`the external magnetic ?eld from the recorded magnetic
`medium (the signal ?eld) causes a change in the direction of
`magnetization in the read element, which in turn causes a
`change in resistance in the read element and a corresponding
`change in the sensed current or voltage.
`A different and more pronounced magnetoresistance,
`called giant magnetoresistance (GMR), has been observed in
`a variety of magnetic multilayered structures, the essential
`feature being at least two ferromagnetic metal layers sepa
`rated by a nonferromagnetic metal layer. This GMR effect
`has been found in a variety of systems, such as Fe/Cr,
`Co/Cu, or Co/Ru multilayers exhibiting strong antiferro
`magnetic coupling of the ferromagnetic layers, as well as in
`essentially uncoupled layered structures in which the mag
`netization orientation in one of the two ferromagnetic layers
`is ?xed or pinned. The physical origin is the same in all types
`of structures: the application of an external magnetic ?eld
`causes a variation in the relative orientation of neighboring
`ferromagnetic layers. This in turn causes a change in the
`spin-dependent scattering of conduction electrons and thus
`the electrical resistance of the structure. The resistance of the
`structure thus changes as the relative alignment of the
`magnetizations of the ferromagnetic layers changes.
`A particularly useful application of GMR is a sandwich
`structure comprising two uncoupled ferromagnetic layers
`separated by a nonmagnetic metallic layer in which the
`magnetization of one of the ferromagnetic layers is pinned.
`The pinning may be achieved by depositing the layer onto an
`iron-manganese (Fe-Mn) layer to exchange couple the two
`layers. This results in a spin valve magnetoresistive (SVMR)
`sensor in which Only the unpinned or free ferromagnetic
`layer is free to rotate in the presence of an external magnetic
`?eld. U.S. Pat. No. 5,206,590, ?led Dec. 11, 1990, and
`assigned to IBM, discloses a basic spin valve MR sensor.
`U.S. Pat. No. 5,159,513, ?led Feb. 8, 1991, and also
`assigned to IBM, discloses a spin valve MR sensor in which
`at least one of the ferromagnetic layers is of cobalt or a
`cobalt alloy, and in which the magnetizations of the two
`ferromagnetic layers are maintained substantially perpen
`dicular to each other at zero externally applied magnetic
`?eld by exchange coupling of the pinned ferromagnetic
`
`20
`
`30
`
`35
`
`40
`
`45
`
`50
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`55
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`60
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`65
`
`2
`layer to an antiferromagnetic layer.
`The spin valve MR sensor that has the most linear
`response and the widest dynamic range is one in which the
`magnetization of the pinned ferromagnetic layer is parallel
`to the signal ?eld and the magnetization of the free ferro
`magnetic layer is perpendicular to the signal ?eld. In the
`case where the spin valve MR sensor is to be used in a
`horizontal magnetic recording disk drive, this means that the
`plane of the sensor is perpendicular to the disk surface with
`the magnetization of the pinned layer oriented perpendicular
`to and the magnetization of the free layer oriented parallel to
`the disk surface. One di?iculty in achieving this magneti
`zation orientation is caused by the dipole ?eld generated by
`the pinned layer. The pinned layer has a net magnetic
`moment and thus essentially acts as a macroscopic dipole
`magnet whose ?eld acts on the free layer. In spin valve MR
`sensors, where the read element is relatively short, the result
`of this magnetostatic coupling is that the magnetization
`direction in the free layer is not uniform. This causes
`portions of the sensor to saturate prematurely in the presence
`of the signal ?eld, which limits the sensor’s dynamic range
`and thus the recording density and overall performance of
`the magnetic recording system.
`What is needed is a spin valve MR sensor with an
`improved pinned ferromagnetic layer that has minimal mag
`netostatic coupling with the free ferromagnetic layer.
`
`SUMMARY OF THE INVENTION
`
`The invention is an improved spin valve MR sensor and
`magnetic recording system incorporating the sensor The
`sensor uses a multi?lm laminated pinned ferromagnetic
`layer in place of the conventional single-layer pinned layer.
`The laminated pinned layer has at least two ferromagnetic
`?lms antiferromagnetically coupled to one another across a
`thin antiferromagnetically (AF) coupling ?lm. By appropri
`ate selection of the thickness of the AF coupling ?lm,
`depending on the material combination selected for the
`ferromagnetic and AF coupling ?lms, the ferromagnetic
`?lms become antiferromagnetically coupled. In the pre
`ferred embodiment, the pinned layer is formed of two ?lms
`of nickel-iron (N i—-Fe) separated by a ruthenium (Ru) ?lm
`having a thickness in the range of approximately 3-6 A.
`Since the pinned ferromagnetic ?lms have their magnetic
`moments aligned antiparallel with one another, the two
`moments can be made to essentially cancel one another by
`making the two ferromagnetic ?lms of substantially the
`same thickness. As a result, there is essentially no dipole
`?eld to adversely affect the free ferromagnetic layer, which
`improves the sensitivity of the sensor and allows higher
`recording density to be achieved in a magnetic recording
`system.
`For a fuller understanding of the nature and advantages of
`the present invention, reference should be made to the
`following detailed description taken together with the
`accompanying ?gures.
`
`BRIEF DESCRIPTION OF THE DRAWING
`
`FIG. 1 is a simpli?ed block diagram of a magnetic
`recording disk drive for use with the spin valve MR sensor
`according to the present invention.
`FIG. 2 is a top view of the disk driverof FIG. 1 with the
`cover removed.
`FIG. 3 is an exploded perspective view of a prior art spin
`valve MR sensor.
`
`TDK Corporation Exhibit 1012 Page 9
`
`

`
`5,465,185
`
`3
`FIG. 4 is a sectional view of the spin valve MR sensor of
`FIG. 3, but rotated 90 degrees.
`FIG. 5 is a sectional view of the spin valve MR sensor
`according to the present invention.
`FIGS. 6A and 6B are graphs of saturation magnetoresis
`tance versus signal ?eld strength for a conventional spin
`valve MR sensor and a spin valve MR sensor according to
`the present invention.
`FIG. 7 is a graph of saturation magnetic ?eld strength
`versus AF coupling ?lm thickness for a laminated Ni——Fe/
`Ru/Ni—Fe structure.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`15
`
`Prior Art
`
`4
`representation purposes only. It should be apparent that disk
`storage systems may contain a large number of disks and
`actuators, and each actuator may support a number of
`sliders. In addition, instead of an air-bearing slider, the head
`carrier may be one which maintains the head in contact or
`near contact with the disk, such as in liquid bearing and other
`contact recording disk drives.
`Referring now to FIG. 3, a prior art spin valve MR sensor
`30 comprises a suitable substrate 31 such as glass, ceramic,
`or a semiconductor, for example, upon which is deposited a
`buffer layer 33, a ?rst thin layer 35 of soft ferromagnetic
`material, a thin nonferromagnetic metallic spacer layer 37,
`and a second thin layer 39 of ferromagnetic material. The
`MR sensor 30 may form part of transducer 25 in the disk
`drive system of FIGS. 1 and 2 and the substrate 31 may be
`the trailing end of the head carrier or slider 20. In the
`absence of an externally applied magnetic field from the
`recorded magnetic medium, the magnetizations of the two
`layers 35, 39 of ferromagnetic material are oriented at an
`angle, preferably of about 90 degrees, with respect to each
`other, as indicated by arrows 32 and 38, respectively. The
`ferromagnetic layer 35 is called the “free” ferromagnetic
`layer in that its magnetization is free to rotate its direction in
`response to an externally applied magnetic ?eld (such as
`magnetic ?eld h as shown in FIG. 3), as shown by the dashed
`arrows on layer 35. The ferromagnetic layer 39 is called the
`“pinned” ferromagnetic layer because its magnetization
`direction is ?xed or pinned in a preferred orientation, as
`shown by the arrow 38. A thin ?lm layer 41 of an exchange
`biasing material having relatively high electrical resistance
`is deposited in direct contact with the ferromagnetic layer 39
`to provide a biasing ?eld by exchange coupling. Layer 41
`thus pins the magnetization of the ferromagnetic layer in a
`preferred direction so that it cannot rotate its direction in the
`presence of an applied external magnetic ?eld having a
`strength in the range of the signal ?eld. The exchange bias
`layer 41 is typically a suitable antiferromagnetic material,
`such as iron~manganese (Fe——Mn) or nickel-manganese
`(Ni-Mn). Alternatively, the second ferromagnetic layer 39
`can be pinned using a hard bias layer (not shown) or by other
`suitable methods as is known in the art.
`FIG. 4 is a sectional view of the structure of FIG. 3 but
`rotated 90 degrees so that the direction of magnetization of
`pinned layer 39 is in the plane of the paper, as shown by
`arrow 38. The pinned ferromagnetic layer 39 has a net
`macroscopic magnetic moment, represented by arrow 38,
`due to its preferred magnetization. The magnetic ?eld
`(shown by ?ux lines 36) associated with this magnetic
`moment has an effect on the free ferromagnetic layer 35,
`which has its direction of magnetization (arrow 35 into the
`paper) formed at an angle of approximately 90 degrees to
`that of the pinned layer. This ?eld from the pinned layer 39
`causes the magnetization in the free layer 35 to be nonuni
`form. Because the free layer 35 is relatively short in the spin
`valve MR sensor, nonuniforrnity of the magnetization can
`cause portions of the sensor to saturate prematurely in the
`presence of an external applied signal ?eld from the mag
`netic medium.
`
`Preferred Embodiments
`
`In the present invention, the single-layer pinned ferro
`magnetic layer is replaced by a laminated structure com
`prising at least two ferromagnetic ?lms separated by a thin
`nonferromagnetic AF coupling ?lm. The two ferromagnetic
`?lms are antiferromagnetically coupled to one another, by
`means of the appropriate type and thickness of AF coupling
`
`30
`
`35
`
`40
`
`45
`
`Although the MR sensor of the present invention will be
`described as embodied in a magnetic disk storage system, as
`shown in FIG. 1, the invention is also applicable to other
`magnetic recording systems, such as a magnetic tape record
`ing system, and to magnetic random access memory systems
`wherein a magnetoresistive element serves as a bit cell.
`Referring to FIG. 1, there is illustrated in sectional view
`25
`a schematic of a prior art disk drive of the type using an MR
`sensor. The disk drive comprises a base 10 to which are
`secured a disk drive motor 12 and an actuator 14, and a cover
`11. The base 10 and cover 11 provide a substantially sealed
`housing for the disk drive. Typically, there is a gasket 13
`located between base 10 and cover 11 and a small breather
`port (not shown) for equalizing pressure between the interior
`of the disk drive and the outside environment. A magnetic
`recording disk 16 is connected to drive motor 12 by means
`of hub 18 to which it is attached for rotation by the drive
`motor 12. A thin continuous lubricant ?lm 50 is maintained
`on the surface of disk 16. A read/write head or transducer 25
`is formed on the trailing end of a carrier, such as an
`air-bearing slider 20. Transducer 25 may be an inductive
`read and Write transducer or an inductive write transducer
`with a magnetoresistive (MR) read transducer of the type to
`be described. The slider 20 is connected to the actuator 14
`by means of a rigid arm 22 and a suspension 24. The
`suspension 24 provides a biasing force which urges the
`slider 20 onto the surface of the recording disk 16. During
`operation of the disk drive, the drive motor 12 rotates the
`disk 16 at a constant speed, and the actuator 14, which is
`typically a linear or rotary voice coil motor (VCM), moves
`the slider 20 generally radially across the surface of the disk
`16 so that the read/write head may access different data
`tracks on disk 16.
`FIG. 2 is a top view of the interior of the disk drive with
`the cover 11 removed, and illustrates in better detail the
`suspension 24 which provides a force to the slider 20 to urge
`it toward the disk 16. The suspension may be a conventional
`type of suspension such as the well-known Watrous suspen
`sion, as described in assignee’s US. Pat. No. 4,167,765.
`This type of suspension also provides a gimbaled attachment
`of the slider which allows the slider to pitch and roll as it
`rides on the air bearing. The data detected from disk 16 by
`the transducer 25 is processed into a data readback signal by
`signal ampli?cation and processing circuitry in the inte
`grated circuit chip 15 located on arm 22. The signals from
`transducer 25 travel via ?ex cable 17 to chip 15, which sends
`its output signals via cable 19.
`The above description of a typical magnetic disk storage
`system, and the accompanying FIGS. 1 and 2, are for
`
`55
`
`60
`
`65
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`TDK Corporation Exhibit 1012 Page 10
`
`

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`5,465,185
`
`5
`?lm, so that their pinned magnetizations are oriented anti
`parallel to one another.
`The preferred embodiment of the spin valve structure
`according to the present invention is shown schematically in
`FIG. 5. A spin ?lm MR sensor 60 as shown in FIG. 5 was
`fabricated by DC magnetron sputter deposition by ?rst
`depositing a 70 A ?lm of tantalum (Ta) as a buffer layer 62
`onto a silicon (Si) substrate 61. Next, a 70 A NimFe19 free
`ferromagnetic layer 63 was deposited in the presence of an
`applied magnetic ?eld so as to have its magnetization
`oriented in the direction of arrow 64 (into the paper in FIG.
`5). A copper (Cu) layer 65 was then deposited onto the free
`Ni—Fe free layer 63 to a thickness of 27 A to serve as the
`nonferromagnetic metallic spacer. While Cu was used as the
`spacer layer in this embodiment, other nonferromagnetic
`metallic materials with high electrical conductivity, such as
`silver (Ag), gold (Au), and their alloys, can be used. The
`pinned ferromagnetic layer 70, which replaces the single
`layer pinned layer 39 in the prior art structure of FIG. 3, is
`a multi?lm laminated structure that comprises a ?rst
`NislFelg ?lm 72 having a thickness of 30 A formed directly
`on the copper spacer layer 65, a 5 A ruthenium (Ru) ?lm 73
`deposited onto the ?rst Ni—Fe ?lm 72, and a second
`NiglFe19 ?lm 74 of 30 A thickness formed on the Ru ?lm 73.
`The two pinned ferromagnetic ?lms 72, 74 were deposited
`in the presence of an applied magnetic ?eld rotated approxi
`mately 90 degrees from the ?eld applied during the depo
`sition of the free ferromagnetic Ni—Fe layer 63. An iron
`manganese (Fe—Mn) ?lm 66 of 90 A thickness was then
`deposited on the second Ni—-—Fe ?lm 74 to exchange couple
`with the second Ni—Fe ?lm 74. Finally, a capping layer 67
`of 25 A of Ru was formed over the Fe—Mn ?lm 66. Other
`suitable capping materials are high resistivity materials,
`such as tantalum (Ta), zirconium (Zr), or alloys of Cu and
`Au.
`FIG. 5 also illustrates schematically the means for con
`necting the MR sensor to sensing circuitry in the magnetic
`recording system. Electrical leads 80 are provided to form a
`circuit path between the MR sensor and a current source 82
`and a sensing means 84. As is well known in the art,
`additional sensor elements, such as transverse and longitu
`dinal bias layers (not shown), may be required to provide an
`optimal MR sensor response circuit. In the preferred
`embodiment, a magnetic signal in the medium is sensed by
`the sensing means 84 detecting the change in resistance,
`deltaR, of the MR element as the magnetization of the free
`ferromagnetic layer 63 rotates in response to the applied
`magnetic signal from the recorded medium.
`The two Ni—Fe ?lms 72, 74 in the laminated pinned layer
`70 have magnetization directions indicated by arrows 76, 78,
`respectively. The antiparallel alignment of the magnetiza
`tions of the two Ni—Fe ?lms 72, 74 is due to an antiferro
`magnetic exchange coupling through Ru AF coupling ?lm
`73. Because of this antiferromagnetic coupling, and because
`the two Ni—-Fe ?lms 72, 74 have substantially the same
`thickness, the magnetic moments of each of the ?lms cancel
`each other so that there is essentially no net magnetic
`moment in the- pinned layer 70. Thus, there is essentially no
`magnetic dipole ?eld generated by the pinned layer 70, and
`thus no magnetic ?eld to affect the direction of magnetiza
`tion 64 of the free ferromagnetic layer 63.
`Referring now to FIGS. 6A and 6B, graphs of saturation
`magnetoresistance deltaR/R (the increase in resistance in
`low magnetic ?elds divided by the high magnetic ?eld
`resistance) versus the signal ?eld strength are shown. FIG.
`6A is the graph for a Conventional spin valve MR sensor (of
`the type shown in FIG. 3) having a single-layer pinned layer,
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`and FIG. 6B is the graph for the structure with the multi?lm
`laminated pinned layer as described and shown in FIG. 5.
`FIG. 6B illustrates that the coercivity (the width of the
`hysteresis curve) of the structure with the laminated pinned
`layer is less than that for the conventional spin valve
`structure so that, with the present invention, smaller signal
`?elds can be detected. In addition to the data of FIG. 6B,
`separate magnetization versus signal ?eld curves demon
`strated that the moment of the laminated pinned layer is
`reduced at low ?elds, which con?rms that this laminated
`pinned layer is comprised of two ?lms coupled antiferro
`magnetically.
`While in the embodiment shown in FIG. 5, the pinned
`ferromagnetic layer 70 comprises two antiferromagnetically
`coupled ?lms 72, 74 separated by a single AF coupling ?lm
`73. The pinned layer 70 can comprise a multiple number of
`ferromagnetic ?lms separated by AF coupling ?lms.
`Depending upon the materials selected for the ferromag
`netic ?lms 72, 74 and AF coupling ?lm 73 in the laminated
`pinned layer 70, there is a preferred AF coupling ?lm
`thickness at which the ferromagnetic ?lms become strongly
`antiferromagnetically coupled. For the case of the preferred
`Ni—-Fe/Ru combination, the thickness of the Ru AF cou
`pling ?lm can be selected with reference to FIG. 7. FIG. 7
`is a graph of the saturation ?eld as a function of Ru spacer
`layer thickness for a 30 A NisoFezolRu combination. The
`peaks of this oscillatory relationship (designated AF in FIG.
`7) are those thicknesses at which antiferromagnetic coupling
`of the two Ni—Fe ?lms occurs, resulting in the desired
`antiparallel alignment of the magnetic moments in the two
`Ni—Fe ?lms. As shown in FIG. 7, the greatest antiferro
`magnetic exchange coupling strength occurs at less than
`approximately 10 A. The AF coupling ?lm thickness must
`not be so thin, however, that a signi?cant number of pin
`holes occur in the ?lm, which would alfect its antiferromag
`netic coupling strength. Thus, in the case of Ru, the preferred
`thickness is in the range of approximately 3-6 A. However,
`for this combination of materials, other Ru AF coupling ?lm
`thicknesses, for example approximately 20 A, may also be
`possible, although the strength of the coupling would be less
`than for the Ru thickness of less than 10 A. The oscillatory
`coupling relationship for selected material combinations, of
`which FIG. 7 is typical, is described in detail by Parkin et al.
`in Phys. Rev. Lett., Vol. 64, p. 2034 (1990).
`If the thicknesses of the two ferromagnetic ?lms 72, 74
`forming the laminated pinned layer 70 are identical, then in
`theory the net moment of the pinned layer 70 would be zero
`because each of the magnetic moments would precisely
`cancel. Because it is not possible to precisely form each of
`the ?lms to the exact same thickness, the net moment of the
`pinned layer 70 will likely be a small but nonzero value as
`a natural result of the normal deposition process. However,
`it may be desirable to deliberately deposit one of the pinned
`ferromagnetic ?lms to a thickness slightly greater than that
`of the other ?lm so that there would be a small nonzero net
`magnetic moment in the pinned layer. This would assure that
`the magnetization of the pinned layer 70 is stable in the
`presence of small magnetic ?elds so that the direction of its
`magnetization is predictable. Also, by controlling the thick
`ness of each of the pinned ferromagnetic ?lms 72, 74, it is
`possible to control the direction of the exchange bias ?eld of
`the Fe——Mn layer 66, which may be desirable in certain MR
`structures. The net moment of the two ?lms 72, 74 will be
`parallel to the moment of the thicker of the two ?lms so that
`if ?lm 74 is made to be the thicker ?lm, then its direction of
`magnetization 78 will be parallel to the applied ?eld during
`deposition. When the Fe-Mn is deposited, its direction of
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`5,465,185
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`7
`magnetization will be antiparallel to the applied ?eld during
`deposition.
`While the laminated pinned layer in the spin valve MR
`sensor has been shown with the preferred materials of
`Ni——Fe and Ru as the ferromagnetic and AF coupling ?lm,
`respectively, other material combinations are possible, such
`as iron/chromium (Fe/Cr), and other ferromagnetic materials
`(such as Co, Fe, Ni, and their alloys, such as Ni-Fe,
`Ni—Co, and Fe—Co) with otherAF coupling ?lms (such as
`Ru, Cr, rhodium (Rh), iridium (Ir), and their alloys). How
`ever, for each such material combination, the oscillatory
`exchange coupling relationship, such as that shown in FIG.
`7 for Ni—Fe/Ru, would have to be determined, if not
`already known, so that the thickness of the AF coupling ?lm
`can be selected to assure antiferromagnetic coupling
`between the two ferromagnetic ?lms. Also, while the pinned
`ferromagnetic ?lm 72 adjacent Cu spacer layer 65 is a single
`Ni—Fe ?lm, it is possible to form this pinned ?lm as a
`two-?lm structure of a Ni—Fe ?lm and a thin Co ?lm
`adjacent the Cu spacer layer 65. Similarly, the free ferro
`magnetic layer 63 may also include a thin Co ?lm adjacent
`the spacer layer 65. These Co ?lms increase the magnetore
`sistance of the sensor but are maintained relatively thin, in
`the range of 2-20 A, to minimize the effect of the relatively
`“hard” magnetic Co material on the permeability of the
`sensor.
`While the present invention has been particularly shown
`and described with reference to the preferred embodiments,
`it will be understood by those skilled in the art that various
`changes in form and detail may be made without departing
`from the spirit, scope, and teaching of the invention. Accord
`ingly, the disclosed invention is to be considered merely as
`illustrative and limited in scope only as speci?ed in the
`appended claims.
`What is claimed is:
`1. A magnetoresistive sensor comprising:
`a ?rst layer and a second layer of ferromagnetic material
`separated by a spacer layer of nonmagnetic material,
`the magnetization direction of said ?rst layer of ferro
`magnetic material being at an angle relative to the
`magnetization direction of said second layer of ferro
`magnetic material at zero applied magnetic ?eld, the
`second layer of ferromagnetic material comprising ?rst
`and second ferromagnetic ?lms antiferromagnetically
`coupled to one another and an antiferromagnetically
`coupling ?lm located between and in contact with the
`?rst and second ferromagnetic ?lms for coupling the
`?rst and second ferromagnetic ?lms together antifer
`romagnetically so that their magnetizations are aligned
`antiparallel with one another and remain antiparallel in
`the-presence of an applied magnetic ?eld; and
`means for maintaining the magnetization of one of the
`ferromagnetic ?lms in the second ferromagnetic layer
`in a ?xed direction in the presence of an applied
`magnetic ?eld, whereby while the magnetization of the
`?rst layer is free to rotate in the presence of an applied
`magnetic ?eld the magnetization directions of the ?rst
`and second ferromagnetic ?lms in the second layer
`remain ?xed and antiparallel to one another.
`2. A magnetoresistive sensor as in claim 1 wherein the
`antiferromagnetically coupling ?lm in the second ferromag
`netic layer consists essentially of Ru.
`3. A magnetoresistive sensor as in claim 2 wherein the Ru
`?lm has a thickness in the range of approximately 3—6
`Angstroms.
`4. A magnetoresistive sensor as in claim 2 wherein the
`?rst and second ferromagnetic ?lms in the second ferromag
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