JP2001102215A - Exchange coupling film and method for production thereof, magnetoresistive effect element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance magnetic conversion characteristics by reducing the Barkhausen noise in a magnetoresistive effect element more effectively through higher exchange coupling strength and structural stability. SOLUTION: An exchange coupling film comprises an antiferromagnetic film 3 of IrMn alloy having composition shown by IrxMn1-x (0.2<x<0.30), and a ferromagnetic film 4 formed sequentially on a substrate 1 through an underlying layer 2 of Ta. The antiferromagnetic film is ordered without requiring heat treatment and has a conventionally unknown Mn rich hexagonal structure of 3H shown by Ir2Mn7 thus realizing a significantly higher exchange coupling field. Exchange coupling field is increased furthermore when the hexagonal structure has a-axis and c-axis falling in such ranges as 2.40 Å<a<2.95 Åand 5.90 Å<c<7.20 Å. The structure is stabilized and a high exchange coupling field is attained when antiferromagnetic film contains twin having thickness of 5.90 Å-300 Å in the direction perpendicular to the twin face at high density and the tin face makes an angle of 10-40 deg. to the film surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exchange coupling film utilizing exchange coupling between a ferromagnetic film and an antiferromagnetic film and a method for manufacturing the same. The present invention relates to a magnetoresistance effect element used for a reproducing magnetic head or the like.

[0002]

2. Description of the Related Art At present, a magnetoresistive element using the anisotropic magnetoresistance effect (AMR) has been put to practical use as a reproducing magnetic head for high-density magnetic recording. As the material of the magnetoresistance effect element, 80 at% Ni-20 at% F
An e-alloy (Permalloy) is commonly used. Barkhausen noise caused by the magnetic domain structure is a problem in the magnetoresistive film made of permalloy, and in order to suppress this, the magnetoresistive film is formed using exchange coupling with an antiferromagnetic film. A method for forming a single magnetic domain is known.

Recently, a spin valve element has been put into practical use as a magnetoresistive element using a giant magnetoresistive (GMR) film capable of obtaining a larger reproduction output. In the spin valve element, the magnetization of the ferromagnetic film is fixed or pinned in one direction so as not to respond to an external magnetic field by utilizing exchange coupling between the ferromagnetic film and the antiferromagnetic film. Antiferromagnetic materials used in spin valve elements are required to have good corrosion resistance, strong exchange coupling force, good thermal stability, and the like. As this antiferromagnetic material, for example, US Pat.
Γ-FeMn alloys are widely known, as described in both 03315 and 5014147.

[0004]

However, the above-mentioned γ-FeMn alloy has a problem that the corrosion resistance is particularly poor, which complicates the manufacturing process and increases the number of steps, lowers the manufacturing yield and reduces the reliability. There has been a problem of causing a decrease. Furthermore, since the γ-FeMn alloy has a low blocking temperature at which the exchange coupling force becomes zero, there is a disadvantage that thermal stability is poor.

As another antiferromagnetic material having good corrosion resistance, oxide-based NiO or the like is disclosed in the above-mentioned US Pat. No. 4,103,133.
Although proposed in the specification of No. 15, there is a problem that the exchange coupling force is weaker than that of the γ-FeMn alloy. As another antiferromagnetic material, MnP capable of obtaining a strong exchange coupling force
A t-ordered alloy and a MnNi ordered alloy have been proposed. However, in order to obtain a strong exchange coupling force, it is necessary to perform a heat treatment at a high temperature, which complicates the manufacturing process and may cause a decrease in yield and reliability.

In order to solve such a problem, the present inventor has conducted various studies on antiferromagnetic materials other than FeMn alloys. As a result, as described in Japanese Patent Application No. 10-46343, the manufacturing process has been described. Strong exchange coupling force can be obtained without performing the heat treatment which is a problem above, and several kinds of Mn suitable for obtaining a highly reliable exchange coupling film in a relatively simple manufacturing process with a high blocking temperature and excellent corrosion resistance are obtained. Alloy found. However, in order to further improve the magnetic characteristics and reliability of a magnetoresistive element using an exchange coupling film, an excellent antiferromagnetic material capable of obtaining a larger exchange coupling magnetic field is required.

Accordingly, an object of the present invention is to provide an exchange-coupling film which also has good corrosion resistance and thermal stability and can realize a larger exchange-coupling magnetic field. Further, an object of the present invention is to provide an exchange coupling film having such a strong exchange coupling force, whereby a Barkhausen noise can be more effectively reduced, and a magnetoresistive element capable of exhibiting high magnetic conversion performance and reliability. Is to provide.

[0008]

The inventor of the present invention has already disclosed in the above-mentioned Japanese Patent Application No. 10-46343 that the structure of the exchange-coupling film has a ferromagnetic material on an antiferromagnetic film made of a Mn alloy thin film. It discloses that by stacking the films, the crystal structure of the antiferromagnetic film can be regularized without heat treatment. Furthermore, studies on the properties of the IrMn alloy as an antiferromagnetic material have been repeated, and various magnetic properties have been evaluated for the relationship between the alloy composition, the microscopic structure, the film forming conditions, and the laminated structure exhibiting good exchange coupling characteristics. As a result of detailed and systematic detailed investigations by X-ray diffraction, high-resolution electron microscopy, etc., IrMn with a specific structure that has not been reported before
The inventors have found that the alloy thin film exhibits excellent exchange coupling characteristics, and have completed the present invention.

That is, the exchange-coupling film of the present invention achieves the above-mentioned object, and comprises an antiferromagnetic film formed on a substrate and a ferromagnetic film laminated thereon. The antiferromagnetic film has an ordered crystal structure and is made of an IrMn alloy having a film composition represented by Ir _x Mn _1-x (x is 0.2 <x <0.30). Features.

In general, the crystal structure obtained by a conventional method of annealing an IrMn alloy having an irregular crystal structure, for example, an Ir20Mn80 alloy, is changed from an irregular fcc to an ordered fcc as previously reported. IrMn as shown in the phase diagram of FIG. 1A.
_This is the L1 ₂ structure represented by ₃ .

On the other hand, in the exchange-coupling film of the present invention, by making the IrMn alloy of the antiferromagnetic material film Mn-rich, 3H represented by Ir ₂ Mn _{7 as} shown in FIG.
Is obtained. This crystal structure is, as far as the inventor of the present application knows, a completely new ordered structure that has not been reported yet, and its film composition Ir _x Mn _1-x is 0.2 <x <0.30.
As long as it is within the range, atomic vacancies are included, and by using the vacancies in the antiferromagnetic film, a larger exchange coupling magnetic field can be obtained as compared with the related art. In addition, it was confirmed that this novel ordered structure was stable even when the occupancy of Ir and Mn at each site was changed.

As a result of electron beam diffraction of the ordered structure shown in FIG. 1B, a diffraction pattern shown in FIG. 2 is obtained. From this, the a-axis and c-axis of the hexagonal structure are calculated as 2.40 ° from the following formulas.
It was found that it was preferable to be in the range of <a <2.95 °, 5.90 ° <c <7.20 °. (Here, a _fcc is the value of the a-axis of the fcc structure.) A = 1 / √2 · a _fcc c = √3 · a _fcc

Therefore, according to the present invention, the crystal structure of the IrMn alloy of the antiferromagnetic film is a hexagonal structure, and its a-axis and c-axis are 2.40 ° <a <2.9, respectively.
An exchange coupling membrane is provided, wherein 5 °, 5.90 ° <c <7.20 °.

Further, according to the present invention, when the antiferromagnetic film has a twin structure and the twin thickness in the direction perpendicular to the twin plane is in the range of 5.90 to 300 °, the structure is further improved. Advantageously, it is stabilized and a large exchange coupling field is obtained.

In this case, if the angle between the twin plane of the antiferromagnetic film and the film surface is in the range of 10 to 40 °,
It is more convenient because the exchange coupling field is further increased.

According to another aspect of the present invention, there is provided an exchange-coupling film characterized in that an antiferromagnetic film and a ferromagnetic film are sequentially laminated on a surface of a substrate to which a tensile stress is applied. A manufacturing method is provided, whereby the exchange coupling membrane of the present invention described above can be easily realized.

Further, according to the present invention, there is provided a magnetoresistive element having an exchange coupling film having an antiferromagnetic film made of an IrMn alloy thin film having the above-mentioned novel ordered crystal structure. By exhibiting a stronger exchange coupling magnetic field than in the past, the magnetoresistance effect element reduces Barkhausen noise, increases thermal and magnetic stability, and improves magnetic conversion characteristics.

[0018]

FIG. 3 shows the structure of an embodiment of an exchange-coupling film according to the present invention, in which an antiferromagnetic film 3 formed on a base layer 2 provided on a substrate 1, and And a ferromagnetic film 4 laminated thereon. On the ferromagnetic film 4, a protective layer 5 of, for example, Ta is provided. For the substrate 1, various known substrate materials such as an amorphous material such as glass and a crystalline material such as Si and MgO are used. The underlayer 2 is for improving the crystallinity of the antiferromagnetic material film formed thereon, and may be formed of various conventionally used materials such as Ta, Ti, Cr, and Zr alloy. it can.

The antiferromagnetic film 3 has a composition of Ir _x Mn.
_1-x , formed from an IrMn alloy represented by 0.2 <x <0.30. As described above, I with slightly increased Mn content
By using the rMn alloy as the antiferromagnetic material and laminating the ferromagnetic film on the antiferromagnetic film, the crystal structure of the antiferromagnetic film 3 is ordered without heat treatment. In addition, it has a novel hexagonal structure shown in FIG. 1B described above. The ordered crystal structure completely different from the disordered fcc to previously reported as shown in FIG. 1A and L1 ₂ structure represented by IrMn ₃ by transformation to the ordered fcc, not previously reported Ir ₂ Mn This is a 3H hexagonal structure represented by ₇ . The existence of such an ordered phase of the antiferromagnetic material can be easily confirmed by a known X-ray diffraction method or electron beam diffraction method.

FIG. 2 shows the result of electron diffraction of the antiferromagnetic film 3, whereby the hexagonal structure shown in FIG. 1B can be confirmed. As can be seen from these drawings,
The values a and c of the a-axis and the c-axis of the hexagonal structure are represented by the following equations, respectively. a = 1 / {2 · a _fcc c = {3 · a _fcc where a _fcc is the value of the a-axis of the fcc structure of the irregular IrMn alloy.
a <2.95 °, 5.90 ° <c <7.20 °.

It has been confirmed that the hexagonal structure contains atomic vacancies as long as the film composition Ir _x Mn _1-x is in the range of 0.2 <x <0.30. A stronger exchange coupling magnetic field can be obtained with the ferromagnetic film 4 than before. Further, it has been found that the hexagonal structure is stable even when the occupancy of Ir and Mn at each site changes.

The antiferromagnetic film 3 and the ferromagnetic film 4 can be formed by various known film forming methods such as a vapor deposition method, a sputtering method, and an MBE (Molecular Beam Epitaxy) method. . The formation of the antiferromagnetic film and the ferromagnetic film can be performed in a magnetic field in order to impart magnetic anisotropy to the exchange coupling film. In another embodiment, the antiferromagnetic material film 3 can be formed directly on the substrate 1 without providing the underlayer 2, and in this case, the antiferromagnetic material film has a similar hexagonal structure. Is obtained.

Further, as shown in FIG. 4, the antiferromagnetic film 3 made of the IrMn alloy film of the present invention has a 3H Ir
It can be formed so as to contain a high density of twins having the bottom surface ((0001) plane) 6 of the Mn ordered phase as a mirror surface. As a result, a stronger exchange coupling magnetic field can be obtained with the ferromagnetic film 4. The twin preferably has a thickness t in the direction perpendicular to the twin plane of 5.90 ° <t <300 °, whereby the structure becomes more stable in addition to the increase in exchange coupling force.

Further, in this twin structure, the angle θ between the twin plane 6 and the surface 7 of the antiferromagnetic film is set to 10 ° <θ <4.
By setting the angle to 0 °, a much larger exchange coupling magnetic field can be realized.

The exchange-coupling film of the present invention can be formed relatively easily by forming each of the above-mentioned film layers in a state where a tensile stress is applied to the substrate surface, as described below. FIG. 5A shows an embodiment of a jig suitable for applying a certain tensile stress to the substrate surface. In this jig 8, side walls 11 of the same constant height are vertically provided on both left and right sides of a flat rectangular base plate 10 corresponding to a rectangular substrate 9, and the upper ends thereof are bent inward at right angles, respectively. Is formed. A screw 13 is screwed from the lower side in the center of the base plate 10, and a straight rod-shaped substrate supporting portion 14 is displaced up and down by turning the screw at a tip protruding from the base plate,
In addition, at this time, it is attached so as to be always horizontal with respect to the base plate and parallel to both side walls 11.

The substrate 9 is attached to the jig 8 as shown in FIG.
The left and right side edges are placed under the substrate presser 12 and mounted so as to be sandwiched between the substrate supporter 14. From this state, the screw 13 is screwed little by little so that the substrate support portion 14
Is raised, and the substrate 9 is curved upwardly convex as shown in FIG. 5B. Thereby, a certain tensile stress is generated on the upper surface of the substrate 9. By thus forming a base layer, an antiferromagnetic material film, a ferromagnetic material film, and a protective layer on the upper surface of the substrate 9 by, for example, sputtering using the conventional method while being mounted on the jig 8 as shown in FIG. An exchange coupling film having an antiferromagnetic film having an ordered crystal structure shown in FIG.
As a jig for applying a tensile stress to the surface of the substrate on which the exchange coupling film is to be formed, various structures other than those shown in FIG. 5 may be used according to the shape and dimensions of the substrate and the film forming conditions. It goes without saying that it can be done.

Further, by providing an electrode on the exchange coupling film of this embodiment using a known technique, a magnetoresistive element can be manufactured. Since this magnetoresistive effect element exhibits a particularly strong exchange coupling force, it is effective for removing Barkhausen noise and fixing or pinning magnetization in a spin valve element.

[0028]

EXAMPLE An about 1% tensile stress was generated on the surface of a Si substrate using a jig shown in FIG. 5, and a 4 nm-thick Ta underlayer was formed using a DC magnetron sputtering apparatus. An antiferromagnetic film made of Ir20Mn80 (at%) having a thickness of 20 nm and a ferromagnetic film made of Co10Fe90 (at%) having a thickness of 10 nm are formed in this order in a static magnetic field of 40 Oe. The exchange coupling film shown in No. 3 was formed. When a magnetization curve of the exchange coupling film with respect to an external magnetic field was measured, the exchange coupling magnetic field was about 300 Oe. Further, when a cross-sectional TEM photograph of this exchange-coupled film was taken, formation of an ordered phase with fine twins was recognized as shown in FIG.

As a comparative example, a 4 nm-thick Ta underlayer and a 10 nm-thick Co10Fe90 (at%) were similarly formed on a Si substrate having no stress load on its surface by using a DC magnetron sputtering apparatus. Ferromagnetic film, thickness 20 nm
Ir20 Mn80 (at%) antiferromagnetic films were sequentially formed in a static magnetic field of 40 Oe to form an exchange coupling film having the same structure as that of FIG. When a magnetization curve was obtained for this exchange coupling film, the exchange coupling magnetic field was about 120 Oe. By comparing these, it was found that the exchange coupling film of the present invention can realize a larger exchange coupling magnetic field.

[0030]

Since the present invention is configured as described above, it has the following effects. According to the exchange-coupling film of the present invention, in addition to having excellent corrosion resistance and a high blocking temperature and being capable of ordering the crystal structure of the antiferromagnetic film without requiring heat treatment, a novel and unique hexagonal structure that has never existed before By taking a crystal structure, it is possible to realize a larger exchange coupling force and a more stable structure than before, and by applying this to a magnetoresistive element, it is possible to more effectively reduce Barkhausen noise. Thus, the magnetic conversion characteristics corresponding to the higher performance of the magnetic recording can be further improved.

[Brief description of the drawings]

FIG. 1A is a schematic diagram showing a crystal structure of a conventional ordered IrMn alloy thin film, and FIG. 1B is a schematic diagram showing an ordered crystal structure of an IrMn antiferromagnetic film of an exchange coupling film according to the present invention. It is.

2 is an electron beam diffraction diagram of an ordered crystal structure of the IrMn antiferromagnetic film of FIG.

FIG. 3 is a cross-sectional view of an exchange coupling film according to the present invention.

FIG. 4 is a diagram showing a twin structure formed in the IrMn antiferromagnetic film in the cross section of FIG. 3;

FIG. 5A is a perspective view illustrating the configuration of a jig used when forming an exchange coupling film by the method of the present invention, and FIG. 5B is a diagram that applies a tensile stress to a substrate surface using the jig. It is a front view showing the state where it did.

FIG. 6 is a cross-sectional TEM photograph of the exchange coupling film of Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Underlayer 3 Antiferromagnetic film 4 Ferromagnetic film 5 Protective layer 6 Twin plane 7 Antiferromagnetic film surface 8 Jig 9 Substrate 10 Base plate 11 Side wall 12 Substrate press 13 Screw 14 Substrate support

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Tatsuo Sawazaki, Inventor Sumitomo Metal Industries, Ltd. 4-33, Kitahama, Chuo-ku, Osaka City, Osaka (72) Inventor Hideyasu Nagai 2-15 Egawa, Shimamoto-cho, Mishima-gun, Osaka −17 Inside Readlight SMI Co., Ltd. (72) Inventor Masaki Ueno 2-15-17 Egawa, Shimamoto-cho, Mishima-gun, Osaka Prefecture (72) Inventor Fuminori Higami, Shimamoto-cho, Mishima-gun, Osaka 2-15-17 Egawa F-term in Readlight SMI Co., Ltd. (reference) 5D034 BA05 CA04 CA08 DA07 5E049 AA01 AA09 AC00 AC05 BA12 BA16 DB02 DB04 DB12

Claims (6)

[Claims] 1. An antiferromagnetic film formed on a substrate and a ferromagnetic film laminated thereon, wherein the antiferromagnetic film has an ordered crystal structure, and Ir _x An exchange coupling film comprising an IrMn alloy having a film composition represented by Mn _1-x (x is 0.2 <x <0.30). 2. The crystal structure is a hexagonal structure, and its a-axis and c-axis are 2.40 ° <a <2.9, respectively.
The exchange coupling membrane according to claim 1, wherein 5 °, 5.90 ° <c <7.20 °. 3. The antiferromagnetic film has a twin structure, and has a twin thickness in the direction perpendicular to the twin plane of 5.90 to 300 °.
The exchange coupling membrane according to claim 1 or 2, wherein 4. The exchange coupling film according to claim 3, wherein an angle between a twin plane of the antiferromagnetic film and the film surface is 10 to 40 °. 5. A magnetoresistive element comprising the exchange coupling film according to claim 1. Description: 6. A method for manufacturing an exchange-coupling film, comprising: laminating an antiferromagnetic film on a surface of a substrate to which a tensile stress is applied, and a ferromagnetic film thereon.