US20170092307A1 - Current-perpendicular-to-plane magneto-resistance effect element - Google Patents

Current-perpendicular-to-plane magneto-resistance effect element Download PDF

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US20170092307A1
US20170092307A1 US15/339,094 US201615339094A US2017092307A1 US 20170092307 A1 US20170092307 A1 US 20170092307A1 US 201615339094 A US201615339094 A US 201615339094A US 2017092307 A1 US2017092307 A1 US 2017092307A1
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layer
substrate
current
metal
orientation
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US9589583B1 (en
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Ye Du
Takao Furubayashi
Yukiko Takahashi
Kazuhiro Hono
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National Institute for Materials Science
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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/127—Structure or manufacture of heads, e.g. inductive
    • G11B5/33—Structure or manufacture of flux-sensitive heads, i.e. for reproduction only; Combination of such heads with means for recording or erasing only
    • G11B5/39—Structure or manufacture of flux-sensitive heads, i.e. for reproduction only; Combination of such heads with means for recording or erasing only using magneto-resistive devices or effects
    • G11B5/3903—Structure or manufacture of flux-sensitive heads, i.e. for reproduction only; Combination of such heads with means for recording or erasing only using magneto-resistive devices or effects using magnetic thin film layers or their effects, the films being part of integrated structures
    • G11B5/3906—Details related to the use of magnetic thin film layers or to their effects
    • G11B5/3929—Disposition of magnetic thin films not used for directly coupling magnetic flux from the track to the MR film or for shielding
    • G11B5/3932—Magnetic biasing films
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y10/00—Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
    • G01R33/06—Measuring direction or magnitude of magnetic fields or magnetic flux using galvano-magnetic devices
    • G01R33/09—Magnetoresistive devices
    • G01R33/093—Magnetoresistive devices using multilayer structures, e.g. giant magnetoresistance sensors
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/02—Recording, reproducing, or erasing methods; Read, write or erase circuits therefor
    • G11B5/09—Digital recording
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/127—Structure or manufacture of heads, e.g. inductive
    • G11B5/1278—Structure or manufacture of heads, e.g. inductive specially adapted for magnetisations perpendicular to the surface of the record carrier
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/127—Structure or manufacture of heads, e.g. inductive
    • G11B5/33—Structure or manufacture of flux-sensitive heads, i.e. for reproduction only; Combination of such heads with means for recording or erasing only
    • G11B5/39—Structure or manufacture of flux-sensitive heads, i.e. for reproduction only; Combination of such heads with means for recording or erasing only using magneto-resistive devices or effects
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/127—Structure or manufacture of heads, e.g. inductive
    • G11B5/33—Structure or manufacture of flux-sensitive heads, i.e. for reproduction only; Combination of such heads with means for recording or erasing only
    • G11B5/39—Structure or manufacture of flux-sensitive heads, i.e. for reproduction only; Combination of such heads with means for recording or erasing only using magneto-resistive devices or effects
    • G11B5/3903—Structure or manufacture of flux-sensitive heads, i.e. for reproduction only; Combination of such heads with means for recording or erasing only using magneto-resistive devices or effects using magnetic thin film layers or their effects, the films being part of integrated structures
    • G11B5/3906—Details related to the use of magnetic thin film layers or to their effects
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N50/00—Galvanomagnetic devices
    • H10N50/10—Magnetoresistive devices
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N50/00—Galvanomagnetic devices
    • H10N50/80—Constructional details
    • H10N50/85—Magnetic active materials
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/127—Structure or manufacture of heads, e.g. inductive
    • G11B5/33—Structure or manufacture of flux-sensitive heads, i.e. for reproduction only; Combination of such heads with means for recording or erasing only
    • G11B5/39—Structure or manufacture of flux-sensitive heads, i.e. for reproduction only; Combination of such heads with means for recording or erasing only using magneto-resistive devices or effects
    • G11B2005/3996—Structure or manufacture of flux-sensitive heads, i.e. for reproduction only; Combination of such heads with means for recording or erasing only using magneto-resistive devices or effects large or giant magnetoresistive effects [GMR], e.g. as generated in spin-valve [SV] devices

Definitions

  • the present invention relates to an element using a current-perpendicular-to-plane giant magneto-resistance effect (CPPGMR) of a thin film having a trilayered structure of a ferromagnetic metal/a nonmagnetic metal/a ferromagnetic metal, in particular, a current-perpendicular-to-plane giant magneto-resistance effect element using an ordinarily usable surface-oxidized Si substrate, silicon substrate, glass substrate, metal substrate or the like instead of an expensive MgO monocrystalline substrate.
  • CPPGMR current-perpendicular-to-plane giant magneto-resistance effect
  • Elements each using a current-perpendicular-to-plane giant magneto-resistance effect (referred to also as a CPPGMR hereinafter) of a thin film having a trilayered structure of a ferromagnetic metal/a nonmagnetic metal/a ferromagnetic metal have been expected for readout heads for magnetic disks.
  • Researches have been made about elements each using a Heusler alloy, which is large in spin polarizability, as each of the ferromagnetic metals.
  • a development has been made about a CPPGMR element using a polycrystalline thin film having a crystal orientation textured into a (110) direction as a layer of the Heusler alloy (for example, Patent Literatures 1 to 3).
  • Patent Literature 1 JP 2010-212631 A
  • Patent Literature 2 JP 2011-35336 A
  • Patent Literature 3 JP 2005-116701 A
  • Non Patent Literature 1 Appl. Phys. Lett. 100, 052405 (2012).
  • Non Patent Literature 2 Appl. Phys. Lett. 101, 252408 (2012).
  • the present invention has been made in light of actual situations of the above-mentioned conventional techniques, and an object of the invention is to provide, without using any MgO monocrystalline substrates, a CPPGMR element more inexpensive and better in performances than CPPGMR elements each using a polycrystalline thin film having a crystal orientation textured to a (110) direction.
  • the present invention provides a CPPGMR element having structural requirements described below.
  • the CPPGMR element of the present invention includes, an orientation layer 12 on a substrate 11 to texture Heusler alloy into a (100) direction, a lower ferromagnetic layer 14 and an upper ferromagnetic layer 16 that each includes a polycrystalline thin film of a Heusler alloy textured into a (100) direction, and that are each stacked on the orientation layer 12 , and a spacer layer 15 sandwiched between the lower ferromagnetic layer 14 and the upper ferromagnetic layer 16 .
  • the substrate 11 is at least one of a surface-oxidized Si substrate, a silicon substrate, a glass substrate, and a metal substrate;
  • the orientation layer 12 includes at least one of MgO, TiN, and NiTa alloys;
  • the lower ferromagnetic layer 14 and the upper ferromagnetic layer 16 each includes a Heusler alloy represented by a composition formula of Co 2 AB wherein A is Cr, Mn, or Fe, or a mixture obtained by mixing two or more of these elements with each other to set the total quantity of the mixed elements to 1, and B is Al, Si, Ga, Ge, In, or Sn, or a mixture obtained by mixing two or more of these elements with each other to set the total quantity of the mixed elements to 1; and the spacer layer 15 is at least one metal selected from the group consisting of Ag, Al, Cu, Au, and Cr, or any alloys of the selected metal(s).
  • the orientation layer 12 , the lower ferromagnetic layer 14 , the upper ferromagnetic layer 16 , and the spacer layer 15 is formed by a sputtering method.
  • an underlying layer 13 for magneto-resistance measurement is laid to be sandwiched between the orientation layer 12 and the lower ferromagnetic layer 14 .
  • the underlying layer 13 can be formed, using at least one metal selected from the group consisting of Ag, Al, Cu, Au, and Cr, or any alloys of the selected metal(s). It is advisable to form the underlying layer 13 by a sputtering method.
  • a cap layer 17 to be stacked on the upper ferromagnetic layer 16 for surface protection may be formed, using at least one metal selected from the group consisting of Ag, Al, Cu, Au, Ru, and Pt, or any alloys of the selected metal(s). It is advisable to form the cap layer 17 by a sputtering method.
  • an orientation layer is laid over a substrate including at least one of a surface-oxidized Si substrate, a silicon substrate, a glass substrate, and a metal substrate, which are inexpensive, without using any MgO monocrystalline substrates to produce a CPPGMR element including a (100)-textured polycrystalline thin film. It has been verified that this production makes the resultant element better in properties than any production using a (110)-textured polycrystalline thin film. Such a structure makes it possible to produce a CPPGMR element more inexpensive and higher in performances.
  • FIG. 1 is a schematic structural view of a CPPGMR element according to an embodiment of the present invention.
  • FIG. 2 is a chart showing an X-ray diffraction pattern of a film obtained by stacking, onto an oxidized Si substrate, respective films of the following from below: MgO (10)/Cr (20)/Ag (50)/CFGG (10)/Ag (7)/CFGG (10)/Ag (5)/Ru (8).
  • FIG. 3 is a schematic sectional view of a CPPGMR element according to an embodiment of the present invention.
  • FIG. 4 is a graph demonstrating a change in the value of “the area of an element” ⁇ “the electric resistance thereof” versus a magnetic field applied thereto.
  • FIG. 5 is a graph demonstrating results of the value ⁇ RA of “the change of the magneto-resistance thereof” ⁇ “the area of an element” versus annealing temperature, in which black squares show results of a (110)-textured orientation film according to a conventional method.
  • FIG. 1 is a schematic structural view of a current-perpendicular-to-plane magneto-resistance effect (CPPGMR) element according to an embodiment of the present invention.
  • the CPPGMR element of the present embodiment is configured by a substrate 11 , an orientation layer 12 , an underlying layer 13 , a lower ferromagnetic layer 14 , a spacer layer 15 , an upper ferromagnetic layer 16 , and a cap layer 17 stacked in this order.
  • CPPGMR current-perpendicular-to-plane magneto-resistance effect
  • the substrate 11 is most preferably a surface-oxidized Si substrate from the viewpoint of costs, but may be a silicon substrate for semiconductor-production, or may be a glass substrate or a metal substrate. It is sufficient for the orientation layer 12 to be a layer having an effect of texturing a Heusler alloy into a (100) direction.
  • the orientation layer 12 is preferably a layer containing at least one of MgO, TiN, and NiTa alloys. Of these components, MgO and TiN are crystalline. Such a crystalline orientation layer is textured into a (100) direction to grow easily, so that the layer itself undergoes (100) orientation to induce the (100) orientation of a Heusler alloy.
  • NiTa is amorphous, NiTa induces the (100) orientation of a Heusler alloy growing on this component.
  • NiTa simultaneously has an effect of breaking off any effect of the crystal orientation.
  • the underlying layer 13 is made of a metal or an alloy, and is to be an electrode for magneto-resistance measurement.
  • the underlying layer 13 the following is usable: a metal containing at least one of Ag, Al, Cu, Au Cr and others; or any alloys of one or more of these metal elements.
  • a different underlying layer may be added below the orientation layer 12 .
  • the lower ferromagnetic layer 14 and the upper ferromagnetic layer 16 each contains a polycrystalline Heusler alloy textured to a (100) direction represented by a composition formula of Co 2 AB wherein A is Cr, Mn, or Fe, or a mixture obtained by mixing two or more of these elements with each other to set the total quantity of the mixed elements to 1, and B is Al, Si, Ga, Ge, In, or Sn, or a mixture obtained by mixing two or more of these elements with each other to set the total quantity of the mixed elements to 1.
  • the Heusler alloy is in particular preferably a Co 2 FeGa 0.5 Ge 0.5 (CFGG) polycrystalline thin film, but may be a Co 2 FeAl 1-x Si x , Co 2 MnSi or Co 2 Fe 1-x Mn x Si polycrystalline thin film.
  • CFGG Co 2 FeGa 0.5 Ge 0.5
  • one Heusler alloy may be used for the upper ferromagnetic layer and the lower ferromagnetic layer.
  • any combination of two or more Heusler alloys may be used, as well as any combination of one or more Heusler alloys with one or more different metals or alloys.
  • the spacer layer 15 is made of a metal or an alloy.
  • the cap layer 17 is made of a metal or an alloy for surface-protection.
  • the spacer layer 15 the following is usable: for example, a metal containing at least one of Ag, Al, Cu, Au, Cr, and others; or any alloys of one or more of these metal elements.
  • the cap layer 17 the following is usable: for example, a metal containing at least one of Ag, Al, Cu, Au, Ru, Pt, and others; or any alloys of one or more of these metal elements.
  • a single material may be used, or two or more materials stacked onto each other may be used.
  • orientation layer 12 it is preferred to form at least one of the orientation layer 12 , the lower ferromagnetic layer 14 , the upper ferromagnetic layer 16 , and the spacer layer by a sputtering method. It is also preferred to anneal the stacked-film at a temperature of 200 to 450° C. for about 15 to 60 minutes to be improved in crystal structure.
  • FIG. 3 is a schematic sectional view of a CPPGMR element according to an example of the present invention.
  • a surface-oxidized Si substrate is used as a substrate 11 ; MgO is used as an orientation layer 12 ; a stacked Cr layer 13 a and Ag layer 13 b , the Cr layer 13 a being positioned below, as an underlying layer 13 ; a polycrystalline (0001)-textured Heusler alloy, Co 2 FeGa 0.5 Ge 0.5 (CFGG), as an upper ferromagnetic layer 14 and a lower ferromagnetic layer 16 ; Ag as a spacer layer 15 ; and a stacked Ag layer 17 a and Ru layer 17 b , the Ag layer 17 a being positioned below, as a cap layer 17 .
  • the CPPGMR element of the present example is an element obtained by forming, onto the oxidized Si substrate, respective films of the following from below: MgO (10)/Cr (20)/Ag (50)/CFGG (10)/Ag (7)/CFGG (10)/Ag (5)/Ru (8).
  • the number in each pair of parentheses represents the film thickness (nm).
  • FIG. 2 is an X-ray diffraction pattern of the stack having the film structure illustrated in FIG. 3 .
  • the structure of the crystal was examined.
  • the layer of each of Cr, Ag, and CFGG was textured into a (100) direction.
  • the sample was annealed at 400° C. for 30 minutes. Thereafter, to measure the electric resistance in the direction perpendicular to the plane of the film, the workpiece was finely worked, as illustrated in FIG.
  • a silicon oxide (SiO 2 ) layer 19 was laid adjacently to the stack composed of the upper ferromagnetic layer 14 , the spacer layer 15 , the lower ferromagnetic layer 16 , and the cap layer 17 .
  • a Cu electrode layer 18 was attached onto the cap layer 17 and the silicon oxide layer 19 .
  • a constant-current source 20 was connected between the underlying layer 13 and the Cu electrode layer 18
  • a voltmeter 21 was connected between the underlying layer 13 and the Cu electrode layer 18 .
  • the constant-current source 20 and the voltmeter 21 were used to examine a change in the electric resistance of the CPPGMR element versus the magnetic field. Furthermore, while the temperature for annealing the sample was varied between 300° C. and 450° C., the variation ⁇ RA of the electric resistance per unit area of the element was examined.
  • FIG. 4 shows a change in the electric resistance of the CPPGMR element versus the magnetic field.
  • the following variation of the electric resistance was obtained per unit area of the element: a variation ⁇ RA of 4.6 [m ⁇ m 2 ].
  • a sample was produced to have a film structure having, over an oxidized Si substrate, respective films of the following: Ta (5)/Cu (250)/Ta (5)/CFGG (5)/Ag (7)/CFGG (5)/Ag (5)/Ru (6), T (2) and Ru (2).
  • the sample was measured in the same way. It was verified about this sample that the crystal orientation of CFGG was textured to (110).
  • FIG. 5 is a graph obtained by plotting the variation ⁇ RA of the electric resistance per unit area of each of the elements versus the annealing temperature T an .
  • the variation ⁇ RA was lowered in the case of T an >400° C.
  • a variation ⁇ RA of 4.3 [m ⁇ m 2 ] was obtained as the average value, which was a value larger than the maximum value 3.5 [m ⁇ m 2 ] according to the conventional technique.
  • a layer of an antiferromagnetic material may be further added, as a pinning layer, onto the upper ferromagnetic layer in the structure illustrated in FIG. 3 .
  • the antiferromagnetic material is, for example, any IrMn alloys or PtMn alloys.
  • This layer structure which has the upper ferromagnetic layer to which the pinning layer is added, makes it possible to restrain magnetization inversion in the upper ferromagnetic layer by exchange anisotropy to stabilize a state that the upper ferromagnetic layer and the lower ferromagnetic layer are magnetized in antiparallel to each other.
  • the pinning layer may be inserted below the lower ferromagnetic layer.
  • CPPGMR current-perpendicular-to-plane magneto-resistance effect

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Abstract

The CPPGMR element of the present invention has an orientation layer 12 formed on a substrate 11 to texture a Heusler alloy into a (100) direction, an underlying layer 13 that is an electrode for magneto-resistance measurement stacked on the orientation layer 12, a lower ferromagnetic layer 14 and an upper ferromagnetic layer 16 each stacked on the underlying layer 13 and made of a Heusler alloy, a spacer layer 15 sandwiched between the lower ferromagnetic layers 14 and the upper ferromagnetic layers 16, and a cap layer 17 stacked on the upper ferromagnetic layer 16 for surface-protection. This manner makes it possible to provide, inexpensively, an element using a current-perpendicular-to-plane giant magneto-resistance effect (CPPGMR) of a thin film having a trilayered structure of a ferromagnetic metal/a nonmagnetic metal/a ferromagnetic metal, thereby showing excellent performances.

Description

    TECHNICAL FIELD
  • The present invention relates to an element using a current-perpendicular-to-plane giant magneto-resistance effect (CPPGMR) of a thin film having a trilayered structure of a ferromagnetic metal/a nonmagnetic metal/a ferromagnetic metal, in particular, a current-perpendicular-to-plane giant magneto-resistance effect element using an ordinarily usable surface-oxidized Si substrate, silicon substrate, glass substrate, metal substrate or the like instead of an expensive MgO monocrystalline substrate.
    • BACKGROUND ART
  • Elements each using a current-perpendicular-to-plane giant magneto-resistance effect (referred to also as a CPPGMR hereinafter) of a thin film having a trilayered structure of a ferromagnetic metal/a nonmagnetic metal/a ferromagnetic metal have been expected for readout heads for magnetic disks. Researches have been made about elements each using a Heusler alloy, which is large in spin polarizability, as each of the ferromagnetic metals. A development has been made about a CPPGMR element using a polycrystalline thin film having a crystal orientation textured into a (110) direction as a layer of the Heusler alloy (for example, Patent Literatures 1 to 3).
  • By contrast, it is demonstrated that in a CPPGMR element, the use of a monocrystalline thin film textured into a (100) direction makes it possible to improve performances of the element (for example, Non Patent Literatures 1 and 2). However, for the production of the monocrystalline thin film, an expensive MgO monocrystalline substrate is required, and thus such methods are impracticable from the viewpoint of costs.
    • CITATION LIST Patent Literatures
  • Patent Literature 1: JP 2010-212631 A
  • Patent Literature 2: JP 2011-35336 A
  • Patent Literature 3: JP 2005-116701 A
    • Non Patent Literatures
  • Non Patent Literature 1: Appl. Phys. Lett. 100, 052405 (2012).
  • Non Patent Literature 2: Appl. Phys. Lett. 101, 252408 (2012).
    • SUMMARY OF INVENTION Technical Problem
  • The present invention has been made in light of actual situations of the above-mentioned conventional techniques, and an object of the invention is to provide, without using any MgO monocrystalline substrates, a CPPGMR element more inexpensive and better in performances than CPPGMR elements each using a polycrystalline thin film having a crystal orientation textured to a (110) direction.
    • Solution to Problem
  • In order to solve the above-mentioned problems, the present invention provides a CPPGMR element having structural requirements described below.
  • For example, as illustrated in FIG. 1, the CPPGMR element of the present invention includes, an orientation layer 12 on a substrate 11 to texture Heusler alloy into a (100) direction, a lower ferromagnetic layer 14 and an upper ferromagnetic layer 16 that each includes a polycrystalline thin film of a Heusler alloy textured into a (100) direction, and that are each stacked on the orientation layer 12, and a spacer layer 15 sandwiched between the lower ferromagnetic layer 14 and the upper ferromagnetic layer 16.
  • In the CPPGMR element of the present invention, it is preferred that: the substrate 11 is at least one of a surface-oxidized Si substrate, a silicon substrate, a glass substrate, and a metal substrate; the orientation layer 12 includes at least one of MgO, TiN, and NiTa alloys; the lower ferromagnetic layer 14 and the upper ferromagnetic layer 16 each includes a Heusler alloy represented by a composition formula of Co2AB wherein A is Cr, Mn, or Fe, or a mixture obtained by mixing two or more of these elements with each other to set the total quantity of the mixed elements to 1, and B is Al, Si, Ga, Ge, In, or Sn, or a mixture obtained by mixing two or more of these elements with each other to set the total quantity of the mixed elements to 1; and the spacer layer 15 is at least one metal selected from the group consisting of Ag, Al, Cu, Au, and Cr, or any alloys of the selected metal(s).
  • In the CPPGMR element of the present invention, it is preferred that at least one of the orientation layer 12, the lower ferromagnetic layer 14, the upper ferromagnetic layer 16, and the spacer layer 15 is formed by a sputtering method.
  • In the CPPGMR element of the present invention, it is further preferred that an underlying layer 13 for magneto-resistance measurement is laid to be sandwiched between the orientation layer 12 and the lower ferromagnetic layer 14. The underlying layer 13 can be formed, using at least one metal selected from the group consisting of Ag, Al, Cu, Au, and Cr, or any alloys of the selected metal(s). It is advisable to form the underlying layer 13 by a sputtering method.
  • In the CPPGMR element of the present invention, it is also preferred that a cap layer 17 to be stacked on the upper ferromagnetic layer 16 for surface protection. The cap layer 17 may be formed, using at least one metal selected from the group consisting of Ag, Al, Cu, Au, Ru, and Pt, or any alloys of the selected metal(s). It is advisable to form the cap layer 17 by a sputtering method.
    • Advantageous Effects of Invention
  • In the present invention, an orientation layer is laid over a substrate including at least one of a surface-oxidized Si substrate, a silicon substrate, a glass substrate, and a metal substrate, which are inexpensive, without using any MgO monocrystalline substrates to produce a CPPGMR element including a (100)-textured polycrystalline thin film. It has been verified that this production makes the resultant element better in properties than any production using a (110)-textured polycrystalline thin film. Such a structure makes it possible to produce a CPPGMR element more inexpensive and higher in performances.
    • BRIEF DESCRIPTION OF DRAWINGS
  • FIG. 1 is a schematic structural view of a CPPGMR element according to an embodiment of the present invention.
  • FIG. 2 is a chart showing an X-ray diffraction pattern of a film obtained by stacking, onto an oxidized Si substrate, respective films of the following from below: MgO (10)/Cr (20)/Ag (50)/CFGG (10)/Ag (7)/CFGG (10)/Ag (5)/Ru (8).
  • FIG. 3 is a schematic sectional view of a CPPGMR element according to an embodiment of the present invention.
  • FIG. 4 is a graph demonstrating a change in the value of “the area of an element”דthe electric resistance thereof” versus a magnetic field applied thereto.
  • FIG. 5 is a graph demonstrating results of the value ΔRA of “the change of the magneto-resistance thereof”דthe area of an element” versus annealing temperature, in which black squares show results of a (110)-textured orientation film according to a conventional method.
    •  DESCRIPTION OF EMBODIMENTS
  • Hereinafter, the present invention will be described, referring to the drawings.
  • FIG. 1 is a schematic structural view of a current-perpendicular-to-plane magneto-resistance effect (CPPGMR) element according to an embodiment of the present invention. In the figure, the CPPGMR element of the present embodiment is configured by a substrate 11, an orientation layer 12, an underlying layer 13, a lower ferromagnetic layer 14, a spacer layer 15, an upper ferromagnetic layer 16, and a cap layer 17 stacked in this order.
  • The substrate 11 is most preferably a surface-oxidized Si substrate from the viewpoint of costs, but may be a silicon substrate for semiconductor-production, or may be a glass substrate or a metal substrate. It is sufficient for the orientation layer 12 to be a layer having an effect of texturing a Heusler alloy into a (100) direction. Thus, the orientation layer 12 is preferably a layer containing at least one of MgO, TiN, and NiTa alloys. Of these components, MgO and TiN are crystalline. Such a crystalline orientation layer is textured into a (100) direction to grow easily, so that the layer itself undergoes (100) orientation to induce the (100) orientation of a Heusler alloy. Although NiTa is amorphous, NiTa induces the (100) orientation of a Heusler alloy growing on this component. When the substrate 11 has a crystal orientation, NiTa simultaneously has an effect of breaking off any effect of the crystal orientation. The underlying layer 13 is made of a metal or an alloy, and is to be an electrode for magneto-resistance measurement. For the underlying layer 13, the following is usable: a metal containing at least one of Ag, Al, Cu, Au Cr and others; or any alloys of one or more of these metal elements. A different underlying layer may be added below the orientation layer 12.
  • The lower ferromagnetic layer 14 and the upper ferromagnetic layer 16 each contains a polycrystalline Heusler alloy textured to a (100) direction represented by a composition formula of Co2AB wherein A is Cr, Mn, or Fe, or a mixture obtained by mixing two or more of these elements with each other to set the total quantity of the mixed elements to 1, and B is Al, Si, Ga, Ge, In, or Sn, or a mixture obtained by mixing two or more of these elements with each other to set the total quantity of the mixed elements to 1. The Heusler alloy is in particular preferably a Co2FeGa0.5Ge0.5 (CFGG) polycrystalline thin film, but may be a Co2FeAl1-xSix, Co2MnSi or Co2Fe1-xMnxSi polycrystalline thin film. For the upper ferromagnetic layer and the lower ferromagnetic layer, one Heusler alloy may be used. Alternatively, any combination of two or more Heusler alloys may be used, as well as any combination of one or more Heusler alloys with one or more different metals or alloys.
  • The spacer layer 15 is made of a metal or an alloy. The cap layer 17 is made of a metal or an alloy for surface-protection. For the spacer layer 15, the following is usable: for example, a metal containing at least one of Ag, Al, Cu, Au, Cr, and others; or any alloys of one or more of these metal elements. For the cap layer 17, the following is usable: for example, a metal containing at least one of Ag, Al, Cu, Au, Ru, Pt, and others; or any alloys of one or more of these metal elements.
  • For each of the orientation layer 12, the underlying layer 13, the spacer layer 15, and the cap layer 17, a single material may be used, or two or more materials stacked onto each other may be used.
  • It is preferred to form at least one of the orientation layer 12, the lower ferromagnetic layer 14, the upper ferromagnetic layer 16, and the spacer layer by a sputtering method. It is also preferred to anneal the stacked-film at a temperature of 200 to 450° C. for about 15 to 60 minutes to be improved in crystal structure.
    • EXAMPLES
  • The following will describe examples of the present invention.
  • FIG. 3 is a schematic sectional view of a CPPGMR element according to an example of the present invention. In the figure, a surface-oxidized Si substrate is used as a substrate 11; MgO is used as an orientation layer 12; a stacked Cr layer 13 a and Ag layer 13 b, the Cr layer 13 a being positioned below, as an underlying layer 13; a polycrystalline (0001)-textured Heusler alloy, Co2FeGa0.5Ge0.5 (CFGG), as an upper ferromagnetic layer 14 and a lower ferromagnetic layer 16; Ag as a spacer layer 15; and a stacked Ag layer 17 a and Ru layer 17 b, the Ag layer 17 a being positioned below, as a cap layer 17.
  • The CPPGMR element of the present example is an element obtained by forming, onto the oxidized Si substrate, respective films of the following from below: MgO (10)/Cr (20)/Ag (50)/CFGG (10)/Ag (7)/CFGG (10)/Ag (5)/Ru (8). The number in each pair of parentheses represents the film thickness (nm). By a sputtering method, the film-formation of the layer structure is attained.
  • FIG. 2 is an X-ray diffraction pattern of the stack having the film structure illustrated in FIG. 3. According to the X-ray diffraction, the structure of the crystal was examined. As a result, it was understood from the results shown in FIG. 2 that the layer of each of Cr, Ag, and CFGG was textured into a (100) direction. In order to improve the thin film in crystal structure, the sample was annealed at 400° C. for 30 minutes. Thereafter, to measure the electric resistance in the direction perpendicular to the plane of the film, the workpiece was finely worked, as illustrated in FIG. 3, and a silicon oxide (SiO2) layer 19 was laid adjacently to the stack composed of the upper ferromagnetic layer 14, the spacer layer 15, the lower ferromagnetic layer 16, and the cap layer 17. Next, a Cu electrode layer 18 was attached onto the cap layer 17 and the silicon oxide layer 19. A constant-current source 20 was connected between the underlying layer 13 and the Cu electrode layer 18, and a voltmeter 21 was connected between the underlying layer 13 and the Cu electrode layer 18. The constant-current source 20 and the voltmeter 21 were used to examine a change in the electric resistance of the CPPGMR element versus the magnetic field. Furthermore, while the temperature for annealing the sample was varied between 300° C. and 450° C., the variation ΔRA of the electric resistance per unit area of the element was examined.
  • FIG. 4 shows a change in the electric resistance of the CPPGMR element versus the magnetic field. When the magnetic field was in the range of about ±200 [Oe](=1000/(4π)A)/m), the following variation of the electric resistance was obtained per unit area of the element: a variation ΔRA of 4.6 [mΩ·μm2].
  • For comparison, without using any MgOs (orientation layers), a sample was produced to have a film structure having, over an oxidized Si substrate, respective films of the following: Ta (5)/Cu (250)/Ta (5)/CFGG (5)/Ag (7)/CFGG (5)/Ag (5)/Ru (6), T (2) and Ru (2). The sample was measured in the same way. It was verified about this sample that the crystal orientation of CFGG was textured to (110).
  • FIG. 5 is a graph obtained by plotting the variation ΔRA of the electric resistance per unit area of each of the elements versus the annealing temperature Tan. About the (110)-textured sample according to the conventional technique, the variation ΔRA was lowered in the case of Tan>400° C. By contrast, about the (100)-textured sample according to the present invention, at a Tan of 400° C., a variation ΔRA of 4.3 [mΩ·μm2] was obtained as the average value, which was a value larger than the maximum value 3.5 [mΩ·μm2] according to the conventional technique.
  • In a modified example of the present invention, a layer of an antiferromagnetic material may be further added, as a pinning layer, onto the upper ferromagnetic layer in the structure illustrated in FIG. 3. The antiferromagnetic material is, for example, any IrMn alloys or PtMn alloys. This layer structure, which has the upper ferromagnetic layer to which the pinning layer is added, makes it possible to restrain magnetization inversion in the upper ferromagnetic layer by exchange anisotropy to stabilize a state that the upper ferromagnetic layer and the lower ferromagnetic layer are magnetized in antiparallel to each other. The pinning layer may be inserted below the lower ferromagnetic layer.
  • In the above-mentioned embodiment, a case has been illustrated which has a film structure of MgO (10)/Cr (20)/Ag (50)/CFGG (10)/Ag (7)/CFGG (10)/Ag (5)/Ru (8). However, the present invention is not limited to this structure. Of course, the film material and the film thickness of each of the layers can be appropriately selected from scopes anticipated by those skilled in the art as far as the selected material and film thickness do not depart from the subject matters of the present invention.
    • INDUSTRIAL APPLICABILITY
  • current-perpendicular-to-plane magneto-resistance effect (CPPGMR), is suitable for being used for a read head for a magnetic disk, and is usable for detecting fine magnetic information pieces.
    • REFERENCE SIGNS LIST
    • 11: substrate
    • 12: orientation layer
    • 13: underlying layer
    • 14: lower ferromagnetic layer
    • 15: spacer layer
    • 16: upper ferromagnetic layer
    • 17: cap layer

Claims (8)

1. A current-perpendicular-to-plane magneto-resistance effect element, comprising:
a substrate comprising at least one of a surface-oxidized Si substrate, a silicon substrate, a glass substrate, and a metal substrate;
an orientation layer formed on the substrate to texture Heusler alloy into a (100) direction;
a lower ferromagnetic layer and an upper ferromagnetic layer that each comprises a polycrystalline thin film of a Heusler alloy textured into a (100) direction, and that are each formed on the orientation layer; and
a spacer layer sandwiched between the lower ferromagnetic layer and the upper ferromagnetic layer,.
wherein the orientation layer comprises at least one of MgO, TiN, and NiTa alloys,
thereby improving a variation of the electric resistance per unit area of the element, compared with that of a (110) textured polycrystalline element not using an orientation layer.
2-3. (canceled)
4. The current-perpendicular-to-plane magneto-resistance effect element according to claim 1, wherein the spacer layer is at least one metal selected from the group consisting of Ag, Al, Cu, Au, and Cr, or any alloys of the selected metal(s).
5. The current-perpendicular-to-plane magneto-resistance effect element according to claim 1, wherein at least one of the orientation layer, the lower ferromagnetic layer, the upper ferromagnetic layer, and the spacer layer is formed by a sputtering method.
6. The current-perpendicular-to-plane magneto-resistance effect element according to claim 1, wherein an underlying layer that is an electrode for magneto-resistance measurement is laid to be sandwiched between the orientation layer and the lower ferromagnetic layer.
7. The current-perpendicular-to-plane magneto-resistance effect element according to claim 6, wherein the underlying layer comprises a metal or an alloy.
8. The current-perpendicular-to-plane magneto-resistance effect element according to claim 1, further comprising a cap layer stacked on the upper ferromagnetic layer for surface-protection.
9. The current-perpendicular-to-plane magneto-resistance effect element according to claim 8, wherein the cap layer comprises at least one metal selected from the group consisting of Ag, Al, Cu, Au, Ru, and Pt, or any alloys of the selected metal(s).
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