Patent Publication Number: US-2022238136-A1

Title: Magnetoresistance effect element and heusler alloy

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a divisional application of U.S. application Ser. No. 16/984,389, filed Aug. 4, 2020, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present disclosure relates to a magnetoresistance effect element and a Heusler alloy. 
     Priority is claimed on Japanese Patent Application No. 2019-146332 filed in Japan on Aug. 8, 2019, the content of which is incorporated herein by reference. 
     Description of Related Art 
     A magnetoresistance effect element is an element whose resistance value changes in a lamination direction due to a magnetoresistance effect. A magnetoresistance effect element includes two ferromagnetic layers and a non-magnetic layer sandwiched therebetween. A magnetoresistance effect element in which a conductor is used for a non-magnetic layer is called a giant magnetoresistance (GMR) element, and a magnetoresistance effect element in which an insulating layer (a tunnel barrier layer, a barrier layer) is used for a non-magnetic layer is called a tunnel magnetoresistance (TMR) element. The magnetoresistance effect element can be applied in various applications such as magnetic sensors, high-frequency components, magnetic heads, and magnetic random access memories (MRAMs). 
     Non-Patent Document 1 describes an example in which a Co 2 FeGa 0.5 Ge 0.5  alloy, which is a Heusler alloy, is used for a ferromagnetic layer of the GMR element. 
     Non-Patent Documents 
     
         
         [Non-patent Document 1] Appl. Phys. Lett. 108, 102408 (2016). 
       
    
     SUMMARY OF THE INVENTION 
     A Heusler alloy has been studied as a material that has a high likelihood of achieving a spin polarization of 100% at room temperature. A Heusler alloy has a high spin polarization and is theoretically expected as a material capable of exhibiting a high magnetoresistance ratio (MR ratio). However, even when a Heusler alloy is used for a ferromagnetic layer of a magnetoresistance effect element, the magnetoresistance effect element cannot achieve the expected MR ratio. 
     The present disclosure has been made in view of the above circumstances, and an objective of the present disclosure is to provide a magnetoresistance effect element and a Heusler alloy in which a state change due to annealing does not easily occur. 
     A magnetoresistance effect element is subjected to an annealing treatment during a manufacturing process. A magnetoresistance effect element is subjected to, for example, an annealing treatment for enhancing crystalline properties of each layer, or an annealing treatment that is performed when it is mounted on an integrated circuit. There are cases in which elements constituting the Heusler alloy diffuse during annealing, thereby causing a change in composition or crystal structure. A change in composition or crystal structure of the Heusler alloy causes a decrease in an MR ratio of the magnetoresistance effect element. Therefore, the inventors of the present disclosure have found that, when a portion of elements constituting a Heusler alloy is substituted with an element having a higher melting point than that of Fe, a state of the Heusler alloy does not easily change due to annealing, and the MR ratio of the magnetoresistance effect element is not easily decreased. The present disclosure provides the following means in order to solve the above problems. 
     [1] A magnetoresistance effect element according to a first aspect includes a first ferromagnetic layer, a second ferromagnetic layer, and a non-magnetic layer positioned between the first ferromagnetic layer and the second ferromagnetic layer, in which at least one of the first ferromagnetic layer and the second ferromagnetic layer is a Heusler alloy in which a portion of elements of an alloy represented by Co 2 Fe α Z β  is substituted with a substitution element, in which Z is one or more elements selected from the group consisting of Al, Si, Ga, Ge, and Sn, α and β satisfy 2.3≤α+β, α&lt;β, and 0.5&lt;α&lt;1.9, and the substitution element is one or more elements selected from the group consisting of elements having a melting point higher than that of Fe among elements of Groups 4 to 10. 
     [2] In the magnetoresistance effect element according to the above aspect, the Heusler alloy may be represented by the following general expression (1). Co 2 (Fe 1−a Y1 a ) α Z β  . . . (1) In expression (1), Y1 is the substitution element, and a satisfies 0&lt;a&lt;0.5. 
     [3] In the magnetoresistance effect element according to the above aspect, the substitution element may be one or more elements selected from the group consisting of Zr, Nb, Mo, Ru, Rh, Pd, Hf, Ta, W, Re, Os, Ir, and Pt. 
     [4] In the magnetoresistance effect element according to the above aspect, the substitution element may be one or more elements selected from the group consisting of Hf, Ta, W, Re, Os, Ir, and Pt. 
     [5] In the magnetoresistance effect element according to the above aspect, the Heusler alloy may be represented by the following general expression (2). Co 2 (Fe 1−a Y1 a ) α (Ga 1−b Z1 b ) β  . . . (2) In expression (2), Y1 is the substitution element, Z1 is one or more elements selected from the group consisting of Al, Si, Ge, and Sn, and 0&lt;a&lt;0.5 and 0.1≤β(1−b) are satisfied. 
     [6] In the magnetoresistance effect element according to the above aspect, b in general expression (2) satisfies b&gt;0.5. 
     [7] In the magnetoresistance effect element according to the above aspect, the Heusler alloy may be represented by the following general expression (3). Co 2 (Fe 1−a Y1 a ) β (Ge 1−c Z2 c ) β  . . . (3) In expression (3), Y1 is the substitution element, Z2 is one or more elements selected from the group consisting of Al, Si, Ga, and Sn, and 0&lt;a&lt;0.5 and 0.1≤β(1−c) are satisfied. 
     [8] In the magnetoresistance effect element according to the above aspect, c in general expression (3) may satisfy c&lt;0.5. 
     [9] In the magnetoresistance effect element according to the above aspect, Z2 may be Ga. 
     [10] In the magnetoresistance effect element according to the above aspect, α and β may satisfy 2.3≤α+β&lt;2.66. 
     [11] In the magnetoresistance effect element according to the above aspect, α and β may satisfy 2.45&lt;α+β&lt;2.66. 
     [12] In the magnetoresistance effect element according to the above aspect, the non-magnetic layer may be configured to contain Ag. 
     [13] In the magnetoresistance effect element according to the above aspect, a NiAl layer containing a NiAl alloy may be configured to be provided between the first ferromagnetic layer and the non-magnetic layer and between the second ferromagnetic layer and the non-magnetic layer. 
     [14] In the magnetoresistance effect element according to the above aspect, a thickness t of the NiAl layer may be 0&lt;t≤0.63 nm. 
     [15] A Heusler alloy according to a second aspect is a Heusler alloy in which a portion of elements of an alloy represented by Co 2 Fe α Z β  is substituted with a substitution element, wherein Z is one or more elements selected from the group consisting of Al, Si, Ga, Ge, and Sn, α and β satisfy 2.3≤α+β, α&lt;β, and 0.5&lt;α&lt;1.9, and the substitution element is one or more elements selected from the group consisting of elements having a melting point higher than that of Fe among elements of Groups 4 to 10. 
     A Heusler alloy in which a state change due to annealing does not easily occur can be obtained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a magnetoresistance effect element according to a first embodiment. 
         FIG. 2A  is an example of a crystal structure of a Heusler alloy represented by a compositional formula of X 2 YZ and having an L2 1  structure. 
         FIG. 2B  is an example of a crystal structure of a Heusler alloy represented by a compositional formula of X 2 YZ and having a B2 structure derived from the L2 1  structure. 
         FIG. 2C  is an example of a crystal structure of a Heusler alloy represented by a compositional formula of X 2 YZ and having an A2 structure derived from the L2 1  structure. 
         FIG. 3  is a cross-sectional view of a magnetoresistance effect element according to a second embodiment. 
         FIG. 4  is a cross-sectional view of a magnetoresistance effect element according to a third embodiment. 
         FIG. 5  is a cross-sectional view of a magnetic recording device according to application example 1. 
         FIG. 6  is a cross-sectional view of a magnetic recording element according to application example 2. 
         FIG. 7  is a cross-sectional view of a magnetic recording element according to application example 3. 
         FIG. 8  is a cross-sectional view of a spin current magnetization rotational element according to application example 4. 
         FIG. 9  is a cross-sectional view of a magnetic domain wall movement element according to application example 5. 
         FIG. 10  is a cross-sectional view of a magnetic domain wall movement element according to application example 6. 
         FIG. 11  is a cross-sectional view of a magnetic domain wall movement element according to application example 7. 
         FIG. 12  is a cross-sectional view of a magnetic domain wall movement element according to application example 8. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, the present embodiment will be described in detail with reference to the drawings as appropriate. In the drawings used in the following description, there are cases in which characteristic portions are appropriately enlarged for convenience of illustration so that characteristics of the present embodiment can be easily understood, and dimensional proportions of respective constituent elements may be different from actual ones. Materials, dimensions, and the like illustrated in the following description are merely examples, and the present disclosure is not limited thereto and can be implemented with appropriate modifications within a range not departing from the gist of the present disclosure. 
     First Embodiment 
       FIG. 1  is a cross-sectional view of the magnetoresistance effect element according to a first embodiment.  FIG. 1  is a cross-sectional view of the magnetoresistance effect element  101  along a lamination direction of each layer of the magnetoresistance effect element. The magnetoresistance effect element  101  includes underlayers  20 , a first ferromagnetic layer  30 , a first NiAl layer  40 , a non-magnetic layer  50 , a second NiAl layer  60 , a second ferromagnetic layer  70 , and a cap layer  80  on a substrate  10 . The non-magnetic layer  50  is positioned between the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . The first NiAl layer  40  is positioned between the first ferromagnetic layer  30  and the non-magnetic layer  50 . The second NiAl layer  60  is positioned between the non-magnetic layer  50  and the second ferromagnetic layer  70 . 
     (Substrate) 
     The substrate  10  is a portion serving as a base of the magnetoresistance effect element  101 . It is preferable to use a highly flat material for the substrate  10 . The substrate  10  may include, for example, a metal oxide single crystal, a silicon single crystal, a silicon single crystal with a thermal oxide film, a sapphire single crystal, a ceramic, quartz, and glass. The material contained in the substrate  10  is not particularly limited as long as it is a material having an appropriate mechanical strength and is suitable for heat treatment and microfabrication. As the metal oxide single crystal, a MgO single crystal is an exemplary example. An epitaxial growth film can be easily formed on a substrate containing a MgO single crystal using, for example, a sputtering method. A magnetoresistance effect element using the epitaxial growth film exhibits large magnetoresistance characteristics. Types of the substrate  10  differ depending on intended products. When a product is a magnetic random access memory (MRAM), the substrate  10  may be, for example, a Si substrate having a circuit structure. When a product is a magnetic head, the substrate  10  may be, for example, an AlTiC substrate that is easy to process. 
     (Underlayer) 
     The underlayers  20  are positioned between the substrate  10  and the first ferromagnetic layer  30 . The underlayers  20  may include, for example, a first underlayer  21 , a second underlayer  22 , and a third underlayer  23  in order from a position near the substrate  10 . 
     The first underlayer  21  is a buffer layer which alleviates a difference between a lattice constant of the substrate  10  and a lattice constant of the second underlayer  22 . A material of the first underlayer  21  may be either a conductive material or an insulating material. The material of the first underlayer  21  also differs depending on a material of the substrate  10  and a material of the second underlayer  22 , but may be, for example, a compound having a (001)-oriented NaCl structure. The compound having an NaCl structure may be, for example, a nitride containing at least one element selected from the group consisting of Ti, Zr, Nb, V, Hf, Ta, Mo, W, B, Al, and Ce, or an oxide containing at least one element selected from the group consisting of Mg, Al, and Ce. 
     The material of the first underlayer  21  may also be, for example, a (002)-oriented perovskite-based conductive oxide represented by a compositional formula of ABO 3 . The perovskite-based conductive oxide may be, for example, an oxide containing at least one element selected from the group consisting of Sr, Ce, Dy, La, K, Ca, Na, Pb, and Ba as the site A and containing at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Nb, Mo, Ru, Ir, Ta, Ce, and Pb as the site B. 
     The second underlayer  22  is a seed layer that enhances crystalline properties of an upper layer laminated on the second underlayer  22 . The second underlayer  22  may contain, for example, at least one selected from the group consisting of MgO, TiN, and NiTa alloys. The second underlayer  22  may be, for example, an alloy containing Co and Fe. The alloy containing Co and Fe may be, for example, Co—Fe or Co—Fe—B. 
     The third underlayer  23  is a buffer layer which alleviates a difference between a lattice constant of the second underlayer  22  and a lattice constant of the first ferromagnetic layer  30 . The third underlayer  23  may contain, for example, a metal element when it is used as an electrode for causing a detection current to flow therethrough. The metal element may be, for example, at least one selected from the group consisting of Ag, Au, Cu, Cr, V, Al, W, and Pt. The third underlayer  23  may be a layer containing any one of a metal, an alloy, an intermetallic compound, a metal boride, a metal carbide, a metal silicide, and a metal phosphide which have a function of generating a spin current due to a spin Hall effect when a current flows therethrough. Further, the third underlayer  23  may be a layer having, for example, a (001)-oriented tetragonal crystal structure or a cubic crystal structure and containing at least one element selected from the group consisting of Al, Cr, Fe, Co, Rh, Pd, Ag, Ir, Pt, Au, Mo, and W. The third underlayer  23  may be an alloy of these metal elements or a laminate of materials consisting of two or more types of these metal elements. The alloy of metal elements may include, for example, a cubic crystal based AgZn alloy, AgMg alloy, CoAl alloy, FeAl alloy, and NiAl alloy. 
     The underlayers  20  function as buffer layers which alleviate a difference in lattice constants between the substrate  10  and the first ferromagnetic layer  30  and enhance crystalline properties of an upper layer formed on the underlayers  20 . The first underlayer  21 , the second underlayer  22 , and third underlayer  23  may be omitted. That is, the underlayers  20  may be omitted or may be one layer or two layers. Also, among the first underlayer  21 , the second underlayer  22 , and the third underlayer  23 , there may be layers formed of the same material. Also, the underlayers  20  are not limited to the three layers and may be four or more layers. 
     (First Ferromagnetic Layer and Second Ferromagnetic Layer) 
     The first ferromagnetic layer  30  and the second ferromagnetic layer  70  are magnetic materials. The first ferromagnetic layer  30  and the second ferromagnetic layer  70  each have magnetization. The magnetoresistance effect element  101  outputs a change in a relative angle between magnetization of the first ferromagnetic layer  30  and magnetization of the second ferromagnetic layer  70  as a change in a resistance value. 
     Magnetization of the second ferromagnetic layer  70  is easier to move than magnetization of the first ferromagnetic layer  30 . When a predetermined external force is applied, a magnetization direction of the first ferromagnetic layer  30  does not change (is fixed) while a magnetization direction of the second ferromagnetic layer  70  changes. When the magnetization direction of the second ferromagnetic layer  70  changes with respect to the magnetization direction of the first ferromagnetic layer  30 , a resistance value of the magnetoresistance effect element  101  changes. In this case, the first ferromagnetic layer  30  may be called a magnetization fixed layer, and the second ferromagnetic layer  70  may be called a magnetization free layer. Hereinafter, a case in which the first ferromagnetic layer  30  is the magnetization fixed layer and the second ferromagnetic layer  70  is the magnetization free layer will be described as an example, but this relationship may be reversed. 
     A difference in ease of movement between the magnetization of the first ferromagnetic layer  30  and the magnetization of the second ferromagnetic layer  70  when a predetermined external force is applied is caused by a difference in coercivity between the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . For example, when a thickness of the second ferromagnetic layer  70  is made smaller than a thickness of the first ferromagnetic layer  30 , a coercivity of the second ferromagnetic layer  70  becomes smaller than a coercivity of the first ferromagnetic layer  30 . Also, for example, an antiferromagnetic layer may be provided on a surface of the first ferromagnetic layer  30  on a side opposite to the non-magnetic layer  50  with a spacer layer interposed therebetween. The first ferromagnetic layer  30 , the spacer layer, and the antiferromagnetic layer form a synthetic antiferromagnetic structure (SAF structure). The synthetic antiferromagnetic structure is formed of two magnetic layers sandwiching a spacer layer therebetween. When the first ferromagnetic layer  30  and the antiferromagnetic layer are antiferromagnetically coupled, a coercivity of the first ferromagnetic layer  30  becomes larger than that in a case without the antiferromagnetic layer. The antiferromagnetic layer may be, for example, IrMn, PtMn, or the like. The spacer layer may contain, for example, at least one selected from the group consisting of Ru, Ir, and Rh. 
     The first ferromagnetic layer  30  and the second ferromagnetic layer  70  are Heusler alloys. A Heusler alloy is a half metal in which electrons passing through the non-magnetic layer  50  have only upward or downward spins and which ideally exhibits a spin polarization of 100%. 
     A ferromagnetic Heusler alloy represented by X 2 YZ is called a full Heusler alloy and is a typical intermetallic compound based on a bcc structure. The ferromagnetic Heusler alloy represented by X 2 YZ has a crystal structure of any one of an L2 1  structure, a B2 structure, and an A2 structure. Compounds represented by the compositional formula X 2 YZ have properties of becoming increasingly crystalline in the order of L2 1  structure&gt;B2 structure&gt;A2 structure. 
       FIGS. 2A to 2C  are examples of crystal structures of a Heusler alloy represented by the compositional formula of X 2 YZ, in which  FIG. 2A  is a crystal of a Heusler alloy having an L2 1  structure,  FIG. 2B  is a B2 structure derived from the L2 1  structure, and  FIG. 2C  is an A2 structure derived from the L2 1  structure. In the L2 1  structure, an element entering the X site, an element entering the Y site, and an element entering the Z site are fixed. In the B2 structure, an element entering the Y site and an element entering the Z site are mixed, and an element entering the X site is fixed. In the A2 structure, an element entering the X site, an element entering the Y site, and an element entering the Z site are mixed. 
     In the Heusler alloy according to the present embodiment, α and β satisfy 2.3≤α+β. α is the number of Fe elements when the number of Co elements is 2 in a state before substitution, and β is the number of Z elements when the number of Co elements is 2 in a state before substitution. In a state after substitution, for example, a is the numbers of Fe elements and substitution elements when the number of Co elements is 2, and p is the number of Z elements to be described below when the number of Co elements is 2. The Heusler alloy according to the present embodiment is out of a stoichiometric composition (α+β=2) of the Heusler alloy of X 2 YZ illustrated in  FIG. 2A . As will be shown in examples to be described below, when a composition of the Heusler alloy is intentionally caused to be out of the stoichiometric composition, a magnetoresistance (MR) ratio tends to be maintained even after an annealing treatment. When a value of α+P becomes excessive with respect to the stoichiometric composition, there is a likelihood that a magnetoresistance (MR) ratio will be maintained even when element diffusion occurs. For α+β, it is preferable that 2.3≤α+β&lt;2.66, and particularly preferable that 2.45&lt;α+β&lt;2.66. 
     In the Heusler alloy according to the present embodiment, α and β satisfy a relationship of α&lt;β. There are cases in which the Fe element is substituted with an element of a Co element site. The substitution of the Fe element for the Co element site is called antisite. The antisite causes a variation in a Fermi level of the Heusler alloy. When the Fermi level varies, half-metal characteristics of the Heusler alloy deteriorate, and a spin polarization thereof decreases. The decrease in spin polarization causes a decrease in the MR ratio of the magnetoresistance effect element  101 . For α and β, it is preferable that α&lt;β&lt;2×α, and particularly preferable that α&lt;β&lt;1.5×α. When β does not become too large with respect to α, disturbing in a crystal structure of the Heusler alloy can be suppressed, and a decrease in the MR ratio of the magnetoresistance effect element  101  can be suppressed. 
     Also, in the Heusler alloy according to the present embodiment, α satisfies a relationship of 0.5&lt;α&lt;1.9. In order to suppress the antisite, for α, it is preferable that 0.8&lt;α&lt;1.33, and particularly preferable that 0.9&lt;α&lt;1.2. 
     Also, in the Heusler alloy according to the present embodiment, some elements of an alloy represented by Co 2 Fe α Z β  is substituted with a substitution element. The Z element is one or more elements selected from the group consisting of Al, Si, Ga, Ge, and Sn. The substitution element is substituted with any one of the Co element, the Fe element, and the Z element. The substitution element is mainly substituted with the Fe element. 
     The substitution element is one or more elements selected from the group consisting of elements having a melting point higher than that of Fe among elements of Groups 4 to 10 in the periodic table. The substitution element is, for example, one or more elements selected from the group consisting of Zr, Nb, Mo, Ru, Rh, Pd, Hf, Ta, W, Re, Os, Ir, and Pt. Also, the substitution element is preferably one or more elements selected from the group consisting of Hf, Ta, W, Re, Os, Ir, and Pt. A crystal structure of the Heusler alloy can be maintained even when an element of Groups 4 to 10 is substituted with the Fe element. Also, there is a tendency for a higher period in the periodic table to correspond to a higher melting point. 
     Here, “melting point” indicates a melting point in a case in which an element is formed as a crystal and exists as a single metal. For example, a melting point of Fe is 1538° C. Also, melting points of the elements of Groups 4 to 10 are shown in table 1 below. 
     
       
         
           
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 Group 4 
                 Group 5 
                 Group 6 
                 Group 7 
                 Group 8 
                 Group 9 
                 Group 10 
               
               
                   
               
             
            
               
                 Period 4 
                 Element 
                 Ti 
                 V 
                 Cr 
                 Mn 
                 Fe 
                 Co 
                 Ni 
               
               
                   
                 Melting 
                 1668 
                 1910 
                 1907 
                 1246 
                 1538 
                 1495 
                 1455 
               
               
                   
                 point (° C.) 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Period 5 
                 Element 
                 Zr 
                 Nb 
                 Mo 
                 Tc 
                 Ru 
                 Rh 
                 Pd 
               
               
                   
                 Melting 
                 1855 
                 2468 
                 2623 
                 2157 
                 2334 
                 1964 
                 1554 
               
               
                   
                 point (° C.) 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Period 6 
                 Element 
                 Hf 
                 Ta 
                 W 
                 Re 
                 Os 
                 Ir 
                 Pt 
               
               
                   
                 Melting 
                 2233 
                 2985 
                 3422 
                 3186 
                 3033 
                 2466 
                 1768 
               
               
                   
                 point (° C.) 
                   
                   
                   
                   
                   
                   
                   
               
               
                   
               
            
           
         
       
     
     When a portion of the Heusler alloy is substituted with an element having a melting point higher than that of Fe among elements of Groups 4 to 10, a melting point of the whole Heusler alloy increases. Therefore, diffusion of the elements constituting the Heusler alloy can be suppressed. 
     The Heusler alloy according to the present embodiment may be represented by, for example, the following general expression (1). 
       Co 2 (Fe 1−a Y1 a ) α Z β   (1)
 
     In expression (1), Y1 is a substitution element. a satisfies 0&lt;a&lt;0.5. 
     Also, the Heusler alloy according to the present embodiment may be represented by, for example, the following general expression (2). 
       Co 2 (Fe 1−a Y1 a ) α (Ga 1−b Z1 b ) β   (2)
 
     In expression (2), Y1 is a substitution element, and Z1 is one or more elements selected from the group consisting of Al, Si, Ge, and Sn. General expression (2) satisfies 0&lt;a&lt;0.5 and 0.1≤β(1−b). General expression (2) corresponds to a case in which a portion of the Z element in general expression (1) is Ga. 
     Ga contributes to ordering of the crystal structure of the Heusler alloy at a low temperature. When the number of Co elements is 2, if Ga is contained in an amount of 0.1 or more, the Heusler alloy is easily ordered even at a low temperature. When a crystal structure of the Heusler alloy is ordered, constituent elements thereof do not easily diffuse into the other layers. On the other hand, an abundance ratio of the Ga element is preferably smaller than an abundance ratio of the Z1 element. That is, it is preferable that b&gt;0.5 be satisfied. Ga has a low melting point, and when too much Ga is contained in the Heusler alloy, a melting point of the Heusler alloy may be lowered, and Ga may diffuse into other layers. 
     The Heusler alloy according to the present embodiment may be represented by, for example, the following general expression (3). 
       CO 2 (Fe 1−a Y1 a ) α (Ge 1−c Z2 c ) β   (3)
 
     In expression (3). Y1 is a substitution element, and Z2 is one or more elements selected from the group consisting of Al, Si, Ga, and Sn. General expression (3) satisfies 0&lt;a&lt;0.5 and 0.1≤β(1−c). 
     Ge is a semiconductor element and has an effect of increasing resistivity of the Heusler alloy. When the Heusler alloy contains Ge, Resistance Area product (RA) of the magnetoresistance effect element increases. For example, a magnetic domain wall movement element to be described below or the like is required to have a large RA. The Ge element is preferably contained in an amount of 0.1 or more when the number of Co elements is 2. An abundance ratio of the Ge element is preferably higher than an abundance ratio of the Z2 element. That is, it is preferable that c&lt;0.5 be satisfied. On the other hand, when the abundance ratio of the Ge element is too large, the resistivity of the Heusler alloy increases and becomes a parasitic resistance component of the magnetoresistance effect element  101 . For β(1−c), it is more preferable that 0.63&lt;β(1−c)&lt;1.26, and particularly preferable that 0.84&lt;β(1−c)&lt;1.26. 
     Also, in general expression (3) described above, the Z2 element may be Ga. In this case, general expression (3) is represented by the following general expression (4). 
       Co 2 (Fe 1−a Y1 a ) α (Ge 1−c Ga c ) β   (4)
 
     In expression (4), Y1 is a substitution element. General expression (4) satisfies 0&lt;a&lt;0.5, 0.1≤β(1−c), and 0.1≤βc. 
     The Heusler alloy of general expression (4) contains Ga and Ge as the Z element. In the Heusler alloy of general expression (4), characteristics as a half metal are enhanced by a synergistic effect of Ga and Ge, and thus a spin polarization thereof is improved. The magnetoresistance effect element  101  using the Heusler alloy of general expression (4) is further increased in the MR ratio due to the above-described synergistic effect of Ga and Ge. 
     In general expression (4), an abundance ratio of the Ge element is preferably higher than an abundance ratio of the Ga element. Also, it is more preferable that general expression (4) satisfy 0.63&lt;β(1−c)&lt;1.26 and particularly preferable that it satisfy 0.84&lt;β(1−c)&lt;1.26. 
     Also, in general expression (3) described above, the Z2 element may be Ga or Mn. In this case, general expression (3) is represented by the following general expression (5). 
       Co 2 (Fe 1−a Y1 a ) α (Ge 1−c Ga d Mn e ) β   (5)
 
     In expression (5), Y1 is a substitution element. General expression (5) satisfies 0&lt;a&lt;0.5, d+e=c&gt;0, 0.1≤β(1−c), 0.1≤βd, and 0.1≤βe. 
     Mn has an effect of increasing the MR ratio of the magnetoresistance effect element  101  when it coexists with Ga and Ge. Even when the Mn element is substituted for the Co element site, half metal characteristics are not easily deteriorated. In general expression (5), an abundance ratio of the Mn element is preferably higher than an abundance ratio of the Ge element. Also, an abundance ratio of the Ga element is preferably higher than an abundance ratio of the Ge element. Specifically, it is preferable that β(1−c) satisfy 0.4&lt;β(1−c)&lt;0.6, βd satisfy 0.2&lt;βd&lt;0.4, and βe satisfy 0.65&lt;βe&lt;0.80. When the Heusler alloy contains Ga, Ge, and Mn, effects due to the respective elements are exhibited, and thereby the MR ratio of the magnetoresistance effect element  101  is further increased. 
     In the Heusler alloy according to the present embodiment, a portion of the Heusler alloy is substituted with an element having a melting point higher than that of Fe among elements of Groups 4 to 10, and a melting point of the whole Heusler alloy increases. As a result, the elements constituting the Heusler alloy do not easily diffuse into other layers even when they are subjected to a treatment such as annealing. That is, in the Heusler alloy, the composition or the crystal structure is not easily changed even after it undergoes annealing or the like and its state can be maintained. 
     Here, a case in which both the first ferromagnetic layer  30  and the second ferromagnetic layer  70  are specific Heusler alloys has been described as an example, but only one of the first ferromagnetic layer  30  and the second ferromagnetic layer  70  may be a specific Heusler alloy. In this case, a ferromagnetic material forming the other of the first ferromagnetic layer  30  or the second ferromagnetic layer  70  may contain, for example, a metal selected from the group consisting of Cr, Mn, Co, Fe, and Ni, an alloy containing one or more of these metals, or an alloy containing these metals and at least one element of B, C, and N. Among these ferromagnetic materials. Co—Fe and Co—Fe—B are preferable. 
     A composition of the Heusler alloy can be measured by an X-ray fluorescence (XRF) method, an inductively coupled plasma (ICP) emission spectroscopy method, an energy dispersive X-ray spectroscopy (EDS) method, a secondary ion mass spectrometry (SIMS) method, an Auger electron spectroscopy (AES) method, or the like. 
     A crystal structure of the Heusler alloy can be measured by an X-ray diffraction (XRD) method, a reflection high-energy electron diffraction (RHEED) method, or the like. For example, in a case of the XRD, when the Heusler alloy has the L21 structure, peaks of (200) and (111) are shown, but when the Heusler alloy has the B2 structure, a (200) peak is shown but a (111) peak is not shown. For example, in a case of RHEED, when the Heusler alloy has the L2 1  structure, streaks of (200) and (111) are shown, but when the Heusler alloy has the B2 structure, a (200) streak is shown, but a (111) streak is not shown. 
     Identification of a site of the substitution element can be measured using an X-ray absorption spectroscopy (XAS) method, an X-ray magnetic circular dichroism (XMCD), a nuclear magnetic resonance (NMR) method, or the like. For example, in a case of the XAS, it suffices to observe an absorption end of Co or Fe. 
     The composition, the crystal structure, and the site identification may be analyzed during (in-situ) or after fabrication of the magnetoresistance effect element  101 , or may be analyzed using one in which only the Heusler alloy is formed on a base material. In a case of the latter, it is preferable that a base material formed of a material that does not contain elements contained in the Heusler alloy be selected and the film thickness of the Heusler alloy be set to about 2 nm to 50 nm although it depends on resolution of analytical instruments. 
     (First NiAl Layer and Second NiAl Layer) 
     The first NiAl layer  40  and the second NiAl layer  60  are layers containing a NiAl alloy. The first NiAl layer  40  is a buffer layer that alleviates lattice mismatching between the first ferromagnetic layer  30  and the non-magnetic layer  50 . The second NiAl layer  60  is a buffer layer that alleviates lattice mismatching between the non-magnetic layer  50  and the second ferromagnetic layer  70 . 
     The first NiAl layer  40  and the second NiAl layer  60  each may have a thickness t of, for example, 0&lt;t≤0.63 nm. When the thickness t is too large, there is a likelihood of spin scattering occurring in electrons moving from the first ferromagnetic layer  30  (the second ferromagnetic layer  70 ) to the second ferromagnetic layer  70  (the first ferromagnetic layer  30 ). When the thickness t is within the above-described range, spin scattering in the moving electrons is suppressed, lattice mismatching between the first ferromagnetic layer  30  and the non-magnetic layer  50  is reduced, and lattice mismatching between the non-magnetic layer  50  and the second ferromagnetic layer  70  is reduced. When the lattice mismatching between the layers is reduced, the MR ratio of the magnetoresistance effect element  101  is improved. 
     (Non-Magnetic Layer) 
     The non-magnetic layer  50  is made of a non-magnetic metal. A material of the non-magnetic layer  50  may be, for example, Cu, Au, Ag, Al, Cr, or the like. The non-magnetic layer  50  preferably contains one or more elements selected from the group consisting of Cu, Au, Ag, Al, and Cr as the main constituent element. The “main constituent element” indicates that a proportion occupied by Cu, Au, Ag, Al, and Cr is 50% or more in the compositional formula. The non-magnetic layer  50  preferably contains Ag, and preferably contains Ag as the main constituent element. Since Ag has a long spin diffusion length, the MR ratio of the magnetoresistance effect element  101  using Ag is further increased. 
     The non-magnetic layer  50  may have a thickness in a range of, for example, 1 nm or more and 10 nm or less. The non-magnetic layer  50  hinders magnetic coupling between the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . 
     Also, the non-magnetic layer  50  may be an insulator or a semiconductor. The non-magnetic insulator may be, for example, a material such as Al 2 O 3 , SiO, MgO, MgAl 2 O 4 , or a material in which a portion of Al, Si, and Mg of the materials described above is substituted with Zn, Be, or the like. These materials have a large band gap and are excellent in insulating properties. When the non-magnetic layer  50  is formed of a non-magnetic insulator, the non-magnetic layer  50  is a tunnel barrier layer. The non-magnetic semiconductor may be, for example, Si, Ge, CulnSe 2 , CuGaSe 2 , Cu(In, Ga)Se 2 , or the like. 
     (Cap Layer) 
     The cap layer  80  is positioned on a side of the magnetoresistance effect element  101  opposite to the substrate  10 . The cap layer  80  is provided to protect the second ferromagnetic layer  70 . The cap layer  80  suppresses diffusion of atoms from the second ferromagnetic layer  70 . Also, the cap layer  80  also contributes to crystal orientations of each layer of the magnetoresistance effect element  101 . When the cap layer  80  is provided, magnetizations of the first ferromagnetic layer  30  and the second ferromagnetic layer  70  are stabilized, and the MR ratio of the magnetoresistance effect element  101  can be improved. 
     The cap layer  80  preferably contains a material having high conductivity so that it can be used as an electrode for causing a detection current to flow therethrough. The cap layer  80  may contain, for example, one or more metal elements of Ru, Ag, Al, Cu, Au, Cr, Mo, Pt, W, Ta, Pd, and Ir, alloys of these metal elements, or a laminate of materials consisting of two or more types of these metal elements. 
     Next, a method of manufacturing the magnetoresistance effect element  101  according to the present embodiment will be described. The magnetoresistance effect element  101  can be obtained by laminating, for example, the underlayers  20  (the first underlayer  21 , the second underlayer  22 , and the third underlayer  23 ), the first ferromagnetic layer  30 , the first NiAl layer  40 , the non-magnetic layer  50 , the second NiAl layer  60 , the second ferromagnetic layer  70 , and the cap layer  80  on the substrate  10  in this order. As a method for film formation of each layer, for example, a sputtering method, a vapor deposition method, a laser ablation method, or a molecular beam epitaxy (MBE) method can be used. 
     Also, the substrate  10  may be annealed after forming the underlayers  20  or after laminating the second ferromagnetic layer  70 . The annealing enhances crystalline properties of each layer. 
     The laminate formed of the first ferromagnetic layer  30 , the non-magnetic layer  50 , and the second ferromagnetic layer  70  constituting the magnetoresistance effect element  101  has a columnar shape. The laminate can be formed in various shapes such as a circle, a square, a triangle, a polygon, and the like in a plan view, and can be manufactured by a known method such as photolithography or ion beam etching. 
     As described above, the magnetoresistance effect element  101  according to the present embodiment uses the above-described Heusler alloy for at least one of the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . As described above, in the Heusler alloy according to the present embodiment, the composition or the crystal structure is not easily changed even after it undergoes annealing or the like and its state can be maintained. A change in composition or crystal structure of the Heusler alloy decreases a spin polarization of the Heusler alloy and causes a decrease in the MR ratio of the magnetoresistance effect element. Since a state change of the Heusler alloy does not easily occur even after it undergoes an annealing treatment, the MR ratio of the magnetoresistance effect element  101  is improved. 
     Second Embodiment 
       FIG. 3  is a cross-sectional view of a magnetoresistance effect element according to a second embodiment. A magnetoresistance effect element  102  is different from the magnetoresistance effect element  101  illustrated in  FIG. 1  in that the first NiAl layer  40  and the second NiAl layer  60  are not provided. In  FIG. 3 , constituents the same as those in  FIG. 1  will be denoted by the same references, and description thereof will be omitted. 
     In the magnetoresistance effect element  102  of the second embodiment, at least one of a first ferromagnetic layer  30  and a second ferromagnetic layer  70  is the Heusler alloy described above. The magnetoresistance effect element  102  of the second embodiment achieves the same effects as in the magnetoresistance effect element  101  of the first embodiment. Also, the magnetoresistance effect element  102  of the second embodiment does not include a first NiAl layer and a second NiAl layer, and the first ferromagnetic layer  30 , a non-magnetic layer  50 , and the second ferromagnetic layer  70  are in direct contact with each other. A magnetoresistance effect is caused by a change in relative angle between magnetization directions of the two ferromagnetic layers sandwiching the non-magnetic layer therebetween. An MR ratio is improved by directly sandwiching the non-magnetic layer  50  between the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . Also, layers exhibiting the magnetoresistance effect are three layers of the first ferromagnetic layer  30 , the second ferromagnetic layer  70 , and the non-magnetic layer  50 , and thus a total thickness of the magnetoresistance effect element  102  is reduced. When a thickness of one magnetoresistance effect element  102  is reduced, a large number of elements can be provided in a same region, and the element is suitable for high recording density. Also, since steps of forming the first NiAl layer  40  and the second NiAl layer  60  are not required, a manufacturing process is simplified. 
     Third Embodiment 
       FIG. 4  is a cross-sectional view of a magnetoresistance effect element according to a third embodiment. A magnetoresistance effect element  103  is different from the magnetoresistance effect element  101  illustrated in  FIG. 1  in that underlayers  20  include a fourth underlayer  24 . Therefore, in  FIG. 4 , constituents the same as those in  FIG. 1  will be denoted by the same references, and description thereof will be omitted. 
     The fourth underlayer  24  is disposed between a third underlayer  23  and a first ferromagnetic layer  30 . The fourth underlayer  24  functions as a seed layer that enhances crystalline properties of the first ferromagnetic layer  30  laminated on the underlayers  20 . The fourth underlayer  24  may be, for example, an alloy containing Co and Fe. When the first ferromagnetic layer  30  is a Heusler alloy, magnetization stability in the vicinity of a laminated interface is low. On the other hand, the alloy containing Co and Fe has high magnetization stability and has high lattice matching with the Heusler alloy forming the first ferromagnetic layer  30 . In the magnetoresistance effect element  103  in which the alloy containing Co and Fe is used for the fourth underlayer  24 , since magnetization of the Heusler alloy forming the first ferromagnetic layer  30  is further stabilized, an MR ratio is improved also at room temperature. The alloy containing Co and Fe may be, for example, Co—Fe or Co—Fe—B. 
     Although embodiments of the present disclosure have been described in detail with reference to the drawings, configurations, combinations thereof, or the like in the respective embodiments are examples, and additions, omissions, substitutions, and other changes to the configurations can be made within a scope not departing from the gist of the present disclosure. 
     The magnetoresistance effect elements  101 ,  102 , and  103  according to the respective embodiments can be used for various applications. The magnetoresistance effect elements  101 ,  102 , and  103  according to the respective embodiments can be applied to, for example, a magnetic head, a magnetic sensor, a magnetic memory, a high-frequency filter, or the like. 
     Next, application examples of the magnetoresistance effect element according to the present embodiment will be described. Further, in the following application examples, the magnetoresistance effect element  101  of the first embodiment is used as the magnetoresistance effect element, but the magnetoresistance effect element is not limited thereto. For example, in the following application examples, the same effects can be obtained also when, for example, the magnetoresistance effect element  102  of the second embodiment and the magnetoresistance effect element  103  of the third embodiment are used. 
       FIG. 5  is a cross-sectional view of a magnetic recording device according to application example 1.  FIG. 5  is a cross-sectional view of the magnetoresistance effect element  101  along the lamination direction of the layers of the magnetoresistance effect element. 
     As illustrated in  FIG. 5 , a magnetic recording device  201  includes a magnetic head  210  and a magnetic recording medium W. In  FIG. 5 , one direction in which the magnetic recording medium W extends is referred to as an X direction, and a direction perpendicular to the X direction is referred to as a Y direction. An XY plane is parallel to a main surface of the magnetic recording medium W. A direction connecting the magnetic recording medium W and the magnetic head  210  and perpendicular to the XY plane is referred to as a Z direction. 
     The magnetic head  210  has an air bearing surface (air bearing surface, medium facing surface) S facing a surface of the magnetic recording medium W. The magnetic head  210  moves in directions of arrow +X and arrow −X along the surface of the magnetic recording medium W at a position separated by a fixed distance from the magnetic recording medium W. The magnetic head  210  includes the magnetoresistance effect element  101  that acts as a magnetic sensor, and a magnetic recording unit (not illustrated). A resistance measuring device  220  is connected to the first ferromagnetic layer  30  and the second ferromagnetic layer  70  of the magnetoresistance effect element  101 . 
     The magnetic recording unit applies a magnetic field to a recording layer W 1  of the magnetic recording medium W and determines a magnetization direction of the recording layer W 1 . That is, the magnetic recording unit performs magnetic recording on the magnetic recording medium W. The magnetoresistance effect element  101  reads information of the magnetization of the recording layer W 1  written by the magnetic recording unit. 
     The magnetic recording medium W includes the recording layer W 1  and a backing layer W 2 . The recording layer W 1  is a portion which performs magnetic recording, and the backing layer W 2  is a magnetic path (magnetic flux passage) which recirculates a writing magnetic flux to the magnetic head  210  again. The recording layer W 1  records magnetic information as a magnetization direction. 
     The second ferromagnetic layer  70  of the magnetoresistance effect element  101  is a magnetization free layer. Therefore, the second ferromagnetic layer  70  exposed on the air bearing surface S is affected by magnetization recorded in the facing recording layer W 1  of the magnetic recording medium W. For example, in  FIG. 5 , a magnetization direction of the second ferromagnetic layer  70  is oriented in a +z direction by being affected by magnetization of the recording layer W 1  oriented in the +z direction. In this case, magnetization directions of the first ferromagnetic layer  30  which is a magnetization fixed layer and the second ferromagnetic layer  70  are parallel to each other. 
     Here, resistance when magnetization directions of the first ferromagnetic layer  30  and the second ferromagnetic layer  70  are parallel is different from resistance when magnetization directions of the first ferromagnetic layer  30  and the second ferromagnetic layer  70  are antiparallel. Therefore, information on the magnetization of the recording layer W 1  can be read as a change in resistance value by measuring resistances of the first ferromagnetic layer  30  and the second ferromagnetic layer  70  using the resistance measuring device  220 . 
     A shape of the magnetoresistance effect element  101  of the magnetic head  210  is not particularly limited. For example, in order to avoid an influence of a leakage magnetic field of the magnetic recording medium W with respect to the first ferromagnetic layer  30  of the magnetoresistance effect element  101 , the first ferromagnetic layer  30  may be installed at a position away from the magnetic recording medium W. 
     The magnetoresistance effect element  101  used in the magnetic head  210  includes the first ferromagnetic layer  30  and the second ferromagnetic layer  70  which are the Heusler alloys described above and thus has a high MR ratio. The magnetic head  210  reads data using a change in resistance value of the magnetoresistance effect element  101 , and when the MR ratio of the magnetoresistance effect element  101  increases, erroneous recognition of data or the like does not easily occur. 
       FIG. 6  is a cross-sectional view of a magnetic recording element according to application example 2.  FIG. 6  is a cross-sectional view of the magnetoresistance effect element  101  along the lamination direction of the layers of the magnetoresistance effect element. 
     As illustrated in  FIG. 6 , a magnetic recording element  202  includes the magnetoresistance effect element  101 , a power supply  230  and a measurement unit  240  which are connected to the first ferromagnetic layer  30  and the second ferromagnetic layer  70  of the magnetoresistance effect element  101 . When the third underlayer  23  of the underlayers  20  has conductivity, the power supply  230  and the measurement unit  240  may be connected to the third underlayer  23  instead of the first ferromagnetic layer  30 . Also, when the cap layer  80  has conductivity, the power supply  230  and the measurement unit  240  may be connected to the cap layer  80  instead of the second ferromagnetic layer  70 . The power supply  230  applies a potential difference to the magnetoresistance effect element  101  in the lamination direction. The measurement unit  240  measures a resistance value of the magnetoresistance effect element  101  in the lamination direction. 
     When a potential difference is generated between the first ferromagnetic layer  30  and the second ferromagnetic layer  70  by the power supply  230 , a current flows in the lamination direction of the magnetoresistance effect element  101 . The current is spin-polarized during passing through the first ferromagnetic layer  30  and becomes a spin-polarized current. The spin-polarized current reaches the second ferromagnetic layer  70  via the non-magnetic layer  50 . Magnetization of the second ferromagnetic layer  70  receives a spin transfer torque (STT) due to the spin-polarized current, and the magnetization is reversed. That is, the magnetic recording element  202  illustrated in  FIG. 6  is a spin transfer torque (STT) type magnetic recording element. 
     When a relative angle between a magnetization direction of the first ferromagnetic layer  30  and a magnetization direction of the second ferromagnetic layer  70  changes, a resistance value of the magnetoresistance effect element  101  in the lamination direction changes. The magnetic recording element  202  reads the resistance value in the lamination direction of the magnetoresistance effect element  101  using the measurement unit  240 . The magnetoresistance effect element  101  in which the first ferromagnetic layer  30  and the second ferromagnetic layer  70  are the Heusler alloys described above has a high MR ratio. When the MR ratio of the magnetoresistance effect element  101  is high, a difference between a resistance value indicating data “1” and a resistance value indicating data “0” becomes large, and thus erroneous reading of the data can be suppressed. 
       FIG. 7  is a cross-sectional view of a magnetic recording element according to application example 3.  FIG. 7  is a cross-sectional view of the magnetoresistance effect element  101  taken along the lamination direction of the layers of the magnetoresistance effect element. 
     As illustrated in  FIG. 7 , a magnetic recording element  203  includes the magnetoresistance effect element  101 , the power supply  230  connected to both ends of the third underlayer  23  of the magnetoresistance effect element  101 , and the measurement unit  240  connected to the third underlayer  23  and the second ferromagnetic layer  70 . The third underlayer  23  is a layer containing any one of a metal, an alloy, an intermetallic compound, a metal boride, a metal carbide, a metal silicide, and a metal phosphide which have a function of generating a spin current due to a spin Hall effect when a current flows therethrough. The third underlayer  23  may be, for example, a layer containing a non-magnetic metal having an atomic number of 39 or higher having d electrons or f electrons in the outermost shell. Also, when the cap layer  80  has conductivity, the measurement unit  240  may be connected to the cap layer  80  instead of the second ferromagnetic layer  70 . The power supply  230  is connected to a first end and a second end of the third underlayer  23 . The power supply  230  applies a potential difference in an in-plane direction between one end portion (the first end) of the third underlayer  23  and an end portion (the second end) thereof on a side opposite to the first end. The measurement unit  240  measures a resistance value of the magnetoresistance effect element  101  in the lamination direction. In the magnetoresistance effect element  101  illustrated in  FIG. 7 , the first ferromagnetic layer  30  is a magnetization free layer and the second ferromagnetic layer  70  is a magnetization fixed layer. 
     When a potential difference is generated between the first end and the second end of the third underlayer  23  by the power supply  230 , a current flows along the third underlayer  23 . When a current flows along the third underlayer  23 , a spin Hall effect occurs due to a spin-orbit interaction. The spin Hall effect is a phenomenon in which moving spins are bent in a direction perpendicular to a direction in which a current flows. The spin Hall effect produces uneven distribution of spins in the third underlayer  23  and induces a spin current in a thickness direction of the third underlayer  23 . The spins are injected into the first ferromagnetic layer  30  from the third underlayer  23  by the spin current. 
     The spins injected into the first ferromagnetic layer  30  impart a spin-orbit torque (SOT) to magnetization of the first ferromagnetic layer  30 . The first ferromagnetic layer  30  receives the spin-orbit torque (SOT), and the magnetization is reversed. That is, the magnetic recording element  203  illustrated in  FIG. 7  is a spin-orbit torque (SOT) type magnetic recording element. 
     When a magnetization direction of the first ferromagnetic layer  30  and a magnetization direction of the second ferromagnetic layer  70  change, a resistance value of the magnetoresistance effect element  101  in the lamination direction changes. The resistance value of the magnetoresistance effect element  101  in the lamination direction is read by the measurement unit  240 . The magnetoresistance effect element  101  in which the first ferromagnetic layer  30  and the second ferromagnetic layer  70  are the Heusler alloys described above has a high MR ratio. When the MR ratio of the magnetoresistance effect element  101  is high, a difference between a resistance value indicating data “1” and a resistance value indicating data “0” becomes large, and thus erroneous reading of the data can be suppressed. 
       FIG. 8  is a cross-sectional view of a spin current magnetization rotational element according to application example 4. 
     A spin current magnetization rotational element  300  is obtained by removing the first NiAl layer  40 , the non-magnetic layer  50 , the second NiAl layer  60 , the second ferromagnetic layer  70 , and the cap layer  80  from the magnetic recording element  203  illustrated in  FIG. 7 . 
     When a potential difference is generated between the first end and the second end of the third underlayer  23  by the power supply  230 , a current flows along the third underlayer  23 . When a current flows along the third underlayer  23 , a spin Hall effect occurs due to a spin-orbit interaction. The spins injected from the third underlayer  23  impart a spin-orbit torque (SOT) to magnetization of the first ferromagnetic layer  30 . A magnetization direction of the first ferromagnetic layer  30  changes due to the spin-orbit torque (SOT). 
     When a magnetization direction of the first ferromagnetic layer  30  changes, polarization of reflected light changes due to a magnetic Kerr effect. Also, when a magnetization direction of the first ferromagnetic layer  30  changes, polarization of transmitted light changes due to a magnetic Faraday effect. The spin current magnetization rotational element  300  can be used as an optical element utilizing the magnetic Kerr effect or the magnetic Faraday effect. 
     In the spin current magnetization rotational element  300 , the first ferromagnetic layer  30  is the Heusler alloy described above. In the Heusler alloy described above, the composition or the crystal structure is not easily changed even after it undergoes annealing or the like and its characteristics can be kept. Generally, a Heusler alloy has a lower damping constant and magnetization is easily rotated compared to an FeCo alloy. When the characteristics of the Heusler alloy are maintained, a magnetization direction of the first ferromagnetic layer  30  can be changed with a low current density. 
       FIG. 9  is a cross-sectional view of a magnetic domain wall movement element (magnetic domain wall displacement type magnetic recording element) according to application example 5. A magnetic domain wall displacement type magnetic recording element  400  includes a first ferromagnetic layer  401 , a second ferromagnetic layer  402 , a non-magnetic layer  403 , a first magnetization fixed layer  404 , and a second magnetization fixed layer  405 . In  FIG. 9 , a direction in which the first ferromagnetic layer  401  extends is referred to as an X direction, a direction perpendicular to the X direction is referred to as a Y direction, and a direction perpendicular to an XY plane is referred to as a Z direction. 
     The non-magnetic layer  403  is sandwiched between the first ferromagnetic layer  401  and the second ferromagnetic layer  402  in the Z direction. The first magnetization fixed layer  404  and the second magnetization fixed layer  405  are connected to the first ferromagnetic layer  401  at a position sandwiching the second ferromagnetic layer  402  and the non-magnetic layer  403  in the X direction. 
     The first ferromagnetic layer  401  is a layer in which information can be magnetically recorded according to a change in internal magnetic state. The first ferromagnetic layer  401  includes a first magnetic domain  401 A and a second magnetic domain  401 B therein. Magnetization of the first ferromagnetic layer  401  at a position overlapping the first magnetization fixed layer  404  or the second magnetization fixed layer  405  in the Z direction is fixed in one direction. Magnetization of the first ferromagnetic layer  401  at a position overlapping the first magnetization fixed layer  404  in the Z direction is fixed, for example, in a +Z direction, and magnetization of the first ferromagnetic layer  401  at a position overlapping the second magnetization fixed layer  405  in the Z direction is fixed, for example, in a −Z direction. As a result, a magnetic domain wall DW is formed at a boundary between the first magnetic domain  401 A and the second magnetic domain  401 B. The first ferromagnetic layer  401  can have the magnetic domain wall DW therein. In the first ferromagnetic layer  401  illustrated in  FIG. 9 , a magnetization M 401A  of the first magnetic domain  401 A is oriented in the +Z direction, and a magnetization M 401B  of the second magnetic domain  401 B is oriented in the −Z direction. 
     The magnetic domain wall displacement type magnetic recording element  400  can record data in a multi-valued or consecutive manner by the position of the magnetic domain wall DW of the first ferromagnetic layer  401 . The data recorded in the first ferromagnetic layer  401  is read as a change in resistance value of the magnetic domain wall displacement type magnetic recording element  400  when a read current is applied. 
     Proportions of the first magnetic domain  401 A and the second magnetic domain  401 B in the first ferromagnetic layer  401  change when the magnetic domain wall DW moves. A magnetization M 402  of the second ferromagnetic layer  402  may be oriented, for example, in the same direction (parallel) as the magnetization M 401A  of the first magnetic domain  401 A, and in an opposite direction (antiparallel) to the magnetization M 401B  of the second magnetic domain  401 B. When the magnetic domain wall DW moves in the +X direction and an area of the first magnetic domain  401 A in a portion overlapping the second ferromagnetic layer  402  in a plan view from the z direction increases, a resistance value of the magnetic domain wall displacement type magnetic recording element  400  decreases. In contrast, when the magnetic domain wall DW moves in the −X direction and an area of the second magnetic domain  401 B in a portion overlapping the second ferromagnetic layer  402  in a plan view from the Z direction increases, a resistance value of the magnetic domain wall displacement type magnetic recording element  400  increases. 
     The magnetic domain wall DW moves when a write current is caused to flow in the x direction of the first ferromagnetic layer  401  or an external magnetic field is applied. For example, when a write current (for example, a current pulse) is applied to the first ferromagnetic layer  401  in the +X direction, since electrons flow in the −X direction that is opposite to a direction of the current, the magnetic domain wall DW moves in the −X direction. When a current flows from the first magnetic domain  401 A toward the second magnetic domain  401 B, electrons spin-polarized in the second magnetic domain  401 B causes the magnetization M 401A  of the first magnetic domain  401 A to be reversed. When the magnetization M 401A  of the first magnetic domain  401 A is reversed, the magnetic domain wall DW moves in the −X direction. 
     As a material of the first ferromagnetic layer  401  and the second ferromagnetic layer  402 , for example, the Heusler alloy described above may be used. Any one of the first ferromagnetic layer  401  and the second ferromagnetic layer  402  may be, for example, a metal selected from the group consisting of Cr, Mn, Co, Fe, and Ni, an alloy containing one or more of these metals, an alloy containing these metals and at least one element of B, C, and N, or the like. Specifically, Co—Fe, Co—Fe—B, and Ni—Fe are exemplary examples. 
     The non-magnetic layer  403  can use a material the same as that of the non-magnetic layer  50  described above. A material the same as that of the second ferromagnetic layer  402  can be used for the first magnetization fixed layer  404  and the second magnetization fixed layer  405 . The first magnetization fixed layer  404  and the second magnetization fixed layer  405  may have a SAF structure. 
     The magnetic domain wall displacement type magnetic recording element  400  in which at least one of the first ferromagnetic layer  401  and the second ferromagnetic layer  402  is the above-mentioned Heusler alloy exhibits a high MR ratio. When the MR ratio of the magnetic domain wall displacement type magnetic recording element  400  is high, a difference between a maximum value and a minimum value of the resistance value of the magnetic domain wall displacement type magnetic recording element  400  increases, and reliability of data is improved. Also, when an RA of the magnetic domain wall displacement type magnetic recording element  400  is large, a moving speed of the magnetic domain wall DW becomes slow and data can be recorded more in an analog manner. In order to increase the RA of the magnetic domain wall displacement type magnetic recording element  400 , it is preferable that at least one of the first ferromagnetic layer  401  and the second ferromagnetic layer  402  satisfy general expression (3). 
       FIG. 10  is a perspective view of a magnetic domain wall movement element (magnetic strip device) according to application example 6. 
     As illustrated in  FIG. 10 , a magnetic strip device  500  includes a magnetic recording medium  510 , a magnetic recording head  520 , and a pulse power supply  530 . The magnetic recording head  520  is provided at a predetermined position above the magnetic recording medium  510 . The pulse power supply  530  is connected to the magnetic recording medium  510  so that a pulse current can be applied in an in-plane direction of the magnetic recording medium  510 . Further, in  FIG. 10 , one direction in which the magnetic recording medium  510  extends is referred to as an X direction, a direction perpendicular to the X direction is referred to as a Y direction, and a direction perpendicular to an XY plane is referred to as a Z direction. 
     The magnetic recording medium  510  includes a magnetic strip  511 , an underlayer  512 , and a substrate  513 . The underlayer  512  is laminated on the substrate  513 , and the magnetic strip  511  is laminated on the underlayer  512 . The magnetic strip  511  is formed in a strip shape having a length in the X direction larger than the width in the Y direction. 
     The magnetic strip  511  is formed of a magnetic material capable of forming a magnetic domain having a magnetization direction different from that of the other portion in a part of a longitudinal direction. The magnetic strip  511  may include, for example, a first magnetic domain  511 A and a second magnetic domain  511 B. A magnetization M 511B  of the second magnetic domain  511 B is oriented in a direction different from a magnetization M 511A  of the first magnetic domain  511 A. A magnetic domain wall DW is formed between the first magnetic domain  511 A and the second magnetic domain  511 B. The second magnetic domain  511 B is generated by the magnetic recording head  520 . 
     The magnetic strip device  500  performs data writing by changing the position of the second magnetic domain  511 B of the magnetic strip  511  using a magnetic field or spin injection magnetization reversal generated by the magnetic recording head  520  while intermittently shifting and moving the magnetic domain wall DW of the magnetic strip  511  by a pulse current supplied from the pulse power supply  530 . The data written in the magnetic strip device  500  can be read by utilizing a magnetoresistance change or a magneto-optical change. When the magnetoresistance change is used, a ferromagnetic layer is provided at a position facing the magnetic strip  511  with a non-magnetic layer sandwiched therebetween. The magnetoresistance change is caused by a difference in relative angle between magnetization of the ferromagnetic layer and magnetization of the magnetic strip  511 . 
     The Heusler alloy described above can be used as a material of the magnetic strip  511 . When the magnetic strip  511  is the Heusler alloy described above, a decrease in performance of the Heusler alloy due to annealing or the like can be suppressed. For example, since the Heusler alloy has a lower damping constant and magnetization is easily rotated compared to an FeCo alloy, the magnetic domain wall DW can be moved with a low current density. Also, when the Heusler alloy satisfying general expression (3) is used for the magnetic strip  511 , an RA of the magnetic strip device  500  can be increased. 
     As a material of the underlayer  512 , ferrite, which is an oxide insulator, more specifically, soft ferrite is preferably used in at least a part thereof. As the soft ferrite, Mn—Zn ferrite, Ni—Zn ferrite. Mn—Ni ferrite, Ni—Zn—Co ferrite can be used. Since the soft ferrite has a high magnetic permeability and a magnetic flux of a magnetic field generated by the magnetic recording head  520  is concentrated thereon, the soft ferrite can efficiently form the second magnetic domain  511 B. A material the same as that of the substrate  10  described above can be used for the substrate  513 . 
       FIG. 11  is a perspective view of a magnetic domain wall movement element (magnetic domain wall movement type spatial light modulator) according to application example 7. 
     As illustrated in  FIG. 11 , a magnetic domain wall movement type spatial light modulator  600  includes a first magnetization fixed layer  610 , a second magnetization fixed layer  620 , and a light modulation layer  630 . In  FIG. 11 , one direction in which the light modulation layer  630  extends is referred to as an X direction, a direction perpendicular to the X direction is referred to as a Y direction, and a direction perpendicular to an XY plane is referred to as a Z direction. 
     A magnetization M 610  of the first magnetization fixed layer  610  and a magnetization M 620  of the second magnetization fixed layer  620  are oriented in different directions. For example, the magnetization M 610  of the first magnetization fixed layer  610  may be oriented in a +Z direction, and the magnetization M 620  of the second magnetization fixed layer  620  may be oriented in a −Z direction. 
     The light modulation layer  630  can be divided into overlapping regions  631  and  636 , initial magnetic domain regions  632  and  635 , and magnetic domain change regions  633  and  634 . 
     The overlapping region  631  is a region overlapping the first magnetization fixed layer  610  in the Z direction, and the overlapping region  636  is a region overlapping the second magnetization fixed layer  620  in the Z direction. A magnetization M 631  of the overlapping region  631  is affected by a leakage magnetic field from the first magnetization fixed layer  610  and may be fixed, for example, in the +Z direction. A magnetization M 636  of the overlapping region  636  is affected by a leakage magnetic field from the second magnetization fixed layer  620  and may be fixed, for example, in the −Z direction. 
     The initial magnetic domain regions  632  and  635  are regions whose magnetizations are fixed in directions different from those of the overlapping regions  631  and  636  by being affected by leakage magnetic fields from the first magnetization fixed layer  610  and the second magnetization fixed layer  620 . A magnetization M 632  of the initial magnetic domain region  632  is affected by a leakage magnetic field from the first magnetization fixed layer  610  and may be fixed, for example, in the −Z direction. A magnetization M 636  of the initial magnetic domain region  635  is affected by a leakage magnetic field from the second magnetization fixed layer  620  and may be fixed, for example, in the +Z direction. 
     The magnetic domain change regions  633  and  634  are regions in which the magnetic domain wall DW can move. A magnetization M 633  of the magnetic domain change region  633  and a magnetization M 634  of the magnetic domain change region  634  are oriented in opposite directions with the magnetic domain wall DW sandwiched therebetween. The magnetization M 633  of the magnetic domain change region  633  is affected by the initial magnetic domain region  632  and may be oriented, for example, in the −Z direction. The magnetization M 634  of the magnetic domain change region  634  is affected by a leakage magnetic field of the initial magnetic domain region  635  and may be fixed, for example, in the +Z direction. A boundary between the magnetic domain change region  633  and the magnetic domain change region  634  is the magnetic domain wall DW. The magnetic domain wall DW moves when a write current is caused to flow in the X direction of the light modulation layer  630  or an external magnetic field is applied. 
     The magnetic domain wall movement type spatial light modulator  600  changes the position of the magnetic domain wall DW while moving the magnetic domain wall DW intermittently. Then, a light L1 is made incident on the light modulation layer  630 , and a light L2 reflected by the light modulation layer  630  is evaluated. Polarization states of the light L2 reflected by portions having different orientation directions of magnetization are different. The magnetic domain wall movement type spatial light modulator  600  can be used as a video display device utilizing a difference in polarization state of the light L2. 
     As a material of the light modulation layer  630 , the Heusler alloy described above can be used. The elements constituting the Heusler alloy do not easily diffuse due to annealing or the like, and thus performance of the Heusler alloy described above does not easily deteriorate. For example, since the Heusler alloy has a lower damping constant and magnetization is easily rotated compared to an FeCo alloy, the magnetic domain wall DW can be moved with a low current density. Also, when the Heusler alloy satisfying general expression (3) is used for the light modulation layer  630 , an RA of the magnetic domain wall movement type spatial light modulator  600  can be increased. As a result, the position of the magnetic domain wall DW can be controlled more precisely, and a video display with higher definition is possible. 
     The same material as the above-described first magnetization fixed layer  404  and the second magnetization fixed layer  405  can be used for the first magnetization fixed layer  610  and the second magnetization fixed layer  620 . 
       FIG. 12  is a perspective view of a high-frequency device according to application example 8. 
     As illustrated in  FIG. 12 , a high-frequency device  700  includes the magnetoresistance effect element  101 , a direct current (DC) power supply  701 , an inductor  702 , a capacitor  703 , an output port  704 , and wirings  705  and  706 . 
     The wiring  705  connects the magnetoresistance effect element  101  and the output port  704 . The wiring  706  branches from the wiring  705  and reaches the ground G via the inductor  702  and the DC power supply  701 . For the DC power supply  701 , the inductor  702 , and the capacitor  703 , known ones can be used. The inductor  702  cuts a high-frequency component of a current and passes an invariant component of the current. The capacitor  703  passes a high-frequency component of a current and cuts an invariant component of the current. The inductor  702  is disposed at a portion in which a flow of the high-frequency current is desired to be suppressed, and the capacitor  703  is disposed at a portion in which a flow of the DC current is desired to be suppressed. 
     When an alternating current (AC) or an alternating magnetic field is applied to the ferromagnetic layer included in the magnetoresistance effect element  101 , magnetization of the second ferromagnetic layer  70  performs precessional motion. Magnetization of the second ferromagnetic layer  70  oscillates strongly when a frequency of a high-frequency current or a high-frequency magnetic field applied to the second ferromagnetic layer  70  is near a ferromagnetic resonance frequency of the second ferromagnetic layer  70 , and does not oscillate as much at a frequency away from the ferromagnetic resonance frequency of the second ferromagnetic layer  70 . This phenomenon is called a ferromagnetic resonance phenomenon. 
     The resistance value of the magnetoresistance effect element  101  changes according to an oscillation of the magnetization of the second ferromagnetic layer  70 . The DC power supply  701  applies a DC current to the magnetoresistance effect element  101 . The DC current flows in the lamination direction of the magnetoresistance effect element  101 . The DC current flows to the ground G through the wirings  706  and  705  and the magnetoresistance effect element  101 . The potential of the magnetoresistance effect element  101  changes according to Ohm&#39;s law. A high-frequency signal is output from the output port  704  according to a change in potential (change in resistance value) of the magnetoresistance effect element  101 . 
     At least one of the first ferromagnetic layer  30  and the second ferromagnetic layer  70  is the Heusler alloy described above. Since the elements constituting the Heusler alloy do not easily diffuse due to annealing or the like, performance of the Heusler alloy described above does not easily deteriorate. For example, the Heusler alloy has a lower damping constant compared to an FeCo alloy, and magnetization can be precessed with a smaller amount of energy. Also, when the MR ratio of the magnetoresistance effect element  101  is high, an intensity of a high-frequency signal oscillated from the magnetoresistance effect element  101  can be made high. 
     EXAMPLES 
     Example 1 
     The magnetoresistance effect element  101  illustrated in  FIG. 1  was fabricated as shown below. The configurations of the layers were as follows. 
     Substrate  10 : MgO single crystal substrate, thickness 0.5 mm 
     Underlayers  20 : Layered structure of First under layer  21  and Second under layer  22  and Third under layer  23   
     First underlayer  21 : MgO, thickness 10 nm 
     Second underlayer  22 : CoFe, thickness 10 nm 
     Third underlayer  23 : Ag, thickness 50 nm 
     First ferromagnetic layer  30 : Co 2 (Fe 0.9 Ta 0.1 ) 1.03 Ga 0.42 Ge 0.85 , thickness 15 nm 
     First NiAl layer  40 : thickness 0.21 nm 
     Non-magnetic layer  50 : Ag, thickness 5 nm 
     Second NiAl layer  60 : thickness 0.21 nm 
     Second ferromagnetic layer  70 : Co 2 (Fe 0.9 Ta 0.1 ) 1.03 Ga 0.42 Ge 0.85 , thickness 5 nm 
     Cap layer  80 : Ru layer, thickness 5 nm 
     The first underlayer  21  (MgO layer) was deposited by heating the substrate  10  to 500° C. and using a sputtering method. The substrate on which the first underlayer  21  was deposited was held at 500° C. for 15 minutes and then allowed to be cooled to room temperature. Next, the second underlayer  22  (CoFe layer) was deposited on the first underlayer  21  using a sputtering method. Next, the third underlayer  23  (Ag layer) was deposited on the second underlayer  22  using a sputtering method, and thereby the underlayers  20  were formed. The substrate  10  on which the underlayers  20  were deposited was annealed at 300° C. for 15 minutes and then allowed to be cooled to room temperature. 
     After allowing it to be cooled, the first ferromagnetic layer  30  (Co 2 (Fe 0.9 Ta 0.1 ) 1.03 Ga 0.42 Ge 0.85 ) was deposited on the underlayers  20  formed on the substrate  10 . The deposition of the first ferromagnetic layer  30  was performed by a co-sputtering method using a CoFeGaGe alloy target and a Ta target as the targets. 
     The first NiAl layer  40  was deposited on the first ferromagnetic layer  30  using a sputtering method. Next, the non-magnetic layer  50  (Ag layer) was deposited on the first NiAl layer  40  using a sputtering method. Next, the second NiAl layer  60  was deposited on the non-magnetic layer  50  in the same manner as the first NiAl layer  40 . Then, the second ferromagnetic layer  70  (Co 2 (Fe 0.9 Ta 0.1 ) 1.03 Ga 0.42 Ge 0.85 ) was deposited on the second NiAl layer  60  in the same manner as the first ferromagnetic layer  30 . The substrate  10  on which the second ferromagnetic layer  70  was formed was annealed at 500° C. for 15 minutes, and then allowed to be cooled to room temperature. 
     After allowing it to be cooled, the cap layer  80  (Ru layer) was deposited on the second ferromagnetic layer  70  formed on the substrate  10  using a sputtering method. In this way, the magnetoresistance effect element  101  illustrated in  FIG. 1  was fabricated. 
     Further, thin film compositions of the first ferromagnetic layer  30  and the second ferromagnetic layer  70  were obtained by performing an ICP emission spectroscopy for the ferromagnetic layer single film deposited on the silicon substrate, and then deposition conditions for desired thin film compositions were determined. 
     The MR ratio of the fabricated magnetoresistance effect element  101  was also measured. As for the MR ratio, a change in resistance value of the magnetoresistance effect element  101  was measured by monitoring a voltage applied to the magnetoresistance effect element  101  with a voltmeter while sweeping a magnetic field from the outside to the magnetoresistance effect element  101  in a state in which a constant current is caused to flow in the lamination direction of the magnetoresistance effect element  101 . The resistance value when magnetization directions of the first ferromagnetic layer  30  and the second ferromagnetic layer  70  are parallel and a resistance value when magnetization directions of the first ferromagnetic layer  30  and the second ferromagnetic layer  70  are antiparallel were measured, and the MR ratio was calculated from the obtained resistance values using the following expression. Measurement of the MR ratio was performed at 300K (room temperature). 
       MR ratio (%)=( R   AP   −R   P )/ R   P ×100
 
     R P  is a resistance value when magnetization directions of the first ferromagnetic layer  30  and the second ferromagnetic layer  70  are parallel, and R AP  is a resistance value when magnetization directions of the first ferromagnetic layer  30  and the second ferromagnetic layer  70  are antiparallel. 
     Examples 2 to 6 
     Examples 2 to 6 are different from example 1 in that a substitution element that is substituted with the Fe element is changed in the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . In example 2, Co 2 (Fe 0.9 W 0.1 ) 1.03 Ga 0.42 Ge 0.85  was used for the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . In example 3, Co 2 (Fe 0.9 Nb 0.1 ) 1.03 Ga 0.42 Ge 0.85  was used for the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . In example 4, Co 2 (Fe 0.9 Mo 0.1 ) 1.03 Ga 0.42 Ge 0.85  was used for the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . In example 5, Co 2 (Fe 0.9 V 0.1 ) 1.03 Ga 0.42 Ge 0.85  was used for the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . In example 6, Co 2 (Fe 0.9 Cr 0.1 ) 1.03 Ga 0.42 Ge 0.85  was used for the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . 
     Examples 7 to 10 
     Examples 7 to 10 are different from example 1 in that a ratio of the substitution element that is substituted with the Fe element is changed in the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . In example 7, Co 2 (Fe 0.8 Ta 0.2 ) 1.03 Ga 0.42 Ge 0.85  was used for the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . In example 8, Co 2 (Fe 0.7 Ta 0.3 ) 1.03 Ga 0.42 Ge 0.85  was used for the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . In example 9, Co 2 (Fe 0.6 Ta 0.4 ) 1.03 Ga 0.42 Ge 0.85  was used for the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . In example 10, Co 2 (Fe 0.5 Ta 0.5 ) 1.03 Ga 0.42 Ge 0.85  was used for the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . 
     Examples 11 to 14 
     Examples 11 to 14 are different from example 1 in that a ratio of the Ge element to the Ga element is changed in the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . In example 11, Co 2 (Fe 0.9 Ta 0.1 ) 1.03 Ga 0.47 Ge 1.00  was used for the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . In example 12, Co 2 (Fe 0.9 Ta 0.1 ) 1.03 Ga 0.42 Ge 1.10  was used for the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . In example 13, Co 2 (Fe 0.9 Ta 0.1 ) 1.03 Ga 0.42 Ge 1.20  was used for the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . In example 14, Co 2 (Fe 0.9 Ta 0.1 ) 1.03 Ga 0.42 Ge 1.30  was used for the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . 
     Examples 15 and 16 
     Examples 15 and 16 are different from example 1 in that portions of the Ga element and the Ge element are substituted with a Mn element in the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . In example 15, Co 2 (Fe 0.9 Ta 0.1 ) 1.03 Ga 0.41 Ge 0.21 Mn 0.80  was used for the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . In example 16, Co 2 (Fe 0.9 Ta 0.1 ) 1.03 Ga 0.41 Ge 0.21 Mn 0.65  was used for the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . 
     Comparative Example 1 
     Comparative example 1 is different from example 1 in that the Fe element is not substituted in the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . In comparative Example 1, Co 2 Fe 1.03 Ga 0.42 Ge 0.85  was used for the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . 
     Comparative Example 2 
     Comparative example 2 is different from example 1 in the composition ratio of each element in the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . In comparative example 2, Co 2 (Fe 0.9 Ta 0.1 ) 1.03 Ga 0.67 Ge 0.6  was used for the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . 
     Comparative Example 3 
     Comparative example 3 is different from example 1 in that the composition ratio of each element is changed and the Fe element is not substituted in the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . In comparative example 3, Co 2 Fe 1.03 Ga 0.67 Ge 0.6  was used for the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . 
     Comparative Example 4 
     Comparative example 4 is different from example 1 in that a ratio of the Ge element to the Ga element is changed in the first ferromagnetic layer  30  and the second ferromagnetic layer  70 . In comparative example 4, Co 2 (Fe 0.9 Ta 0.1 ) 1.03 Ga 0.42 Ge 0.75  was used. 
     The results of MR ratios in examples 1 to 16 and comparative examples 1 to 4 are shown in table 2 below. As shown in table 2, the magnetoresistance effect elements of examples 1 to 16 all had a higher MR ratio than the magnetoresistance effect elements of comparative examples 1 to 4. That is, it can be said that a state of the high MR ratio can be maintained in the magnetoresistance effect elements of examples 1 to 16 even after they undergo the annealing treatment at 500° C. for 15 minutes, and it can be said that a state change of the Heusler alloy due to the annealing does not occur. 
     
       
         
           
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                 MR ratio 
               
               
                   
                 Compositional formula 
                 (%) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Example 1 
                 Co 2 (Fe 0.9 Ta 0.1 ) 1.03 Ga 0.42 Ge 0.85   
                 30.2 
               
               
                 Example 2 
                 Co 2 (Fe 0.9 W 0.1 ) 1.03 Ga 0.42 Ge 0.85   
                 32.5 
               
               
                 Example 3 
                 Co 2 (Fe 0.9 Nb 0.1 ) 1.03 Ga 0.42 Ge 0.85   
                 28.3 
               
               
                 Example 4 
                 Co 2 (Fe 0.9 Mo 0.1 ) 1.03 Ga 0.42 Ge 0.85   
                 29.4 
               
               
                 Example 5 
                 Co 2 (Fe 0.9 V 0.1 ) 1.03 Ga 0.42 Ge 0.85   
                 26.3 
               
               
                 Example 6 
                 Co 2 (Fe 0.9 Cr 0.1 ) 1.03 Ga 0.42 Ge 0.85   
                 26.1 
               
               
                 Example 7 
                 Co 2 (Fe 0.8 Ta 0.2 ) 1.03 Ga 0.42 Ge 0.85   
                 31.6 
               
               
                 Example 8 
                 Co 2 (Fe 0.7 Ta 0.3 ) 1.03 Ga 0.42 Ge 0.85   
                 30.5 
               
               
                 Example 9 
                 Co 2 (Fe 0.6 Ta 0.4 ) 1.03 Ga 0.42 Ge 0.85   
                 28.4 
               
               
                 Example 10 
                 Co 2 (Fe 0.5 Ta 0.5 ) 1.03 Ga 0.42 Ge 0.85   
                 21.0 
               
               
                 Example 11 
                 Co 2 (Fe 0.9 Ta 0.1 ) 1.03 Ga 0.42 Ge 1.00   
                 31.1 
               
               
                 Example 12 
                 Co 2 (Fe 0.9 Ta 0.1 ) 1.03 Ga 0.42 Ge 1.10   
                 31.3 
               
               
                 Example 13 
                 Co 2 (Fe 0.9 Ta 0.1 ) 1.03 Ga 0.42 Ge 1.20   
                 28.8 
               
               
                 Example 14 
                 Co 2 (Fe 0.9 Ta 0.1 ) 1.03 Ga 0.42 Ge 1.30   
                 21.1 
               
               
                 Example 15 
                 Co 2 (Fe 0.9 Ta 0.1 ) 1.03 Ga 0.41 Ge 0.21 Mn 0.80   
                 25.3 
               
               
                 Example 16 
                 Co 2 (Fe 0.9 Ta 0.1 ) 1.03 Ga 0.41 Ge 0.21 Mn 0.65   
                 22.8 
               
               
                 Comparative 
                 Co 2 Fe 1.03 Ga 0.42 Ge 0.85   
                 20.2 
               
               
                 example 1 
                   
                   
               
               
                 Comparative 
                 Co 2 (Fe 0.9 Ta 0.1 ) 1.03 Ga 0.67 Ge 0.6   
                 19.2 
               
               
                 example 2 
                   
                   
               
               
                 Comparative 
                 Co 2 Fe 1.03 Ga 0.67 Ge 0.6   
                 16.5 
               
               
                 example 3 
                   
                   
               
               
                 Comparative 
                 Co 2 (Fe 0.9 Ta 0.1 ) 1.03 Ga 0.42 Ge 0.75   
                 20.4 
               
               
                 example 4 
               
               
                   
               
            
           
         
       
     
     Examples 17 to 21 
     Examples 17 to 21 are different from example 1 in that Co 2 (Fe 0.9 Ta 0.1 ) 1.03 Ga 0.42 Ge 0.85  is used for the first ferromagnetic layer  30  and the second ferromagnetic layer  70 , and thicknesses of the first NiAl layer  40  and the second NiAl layer  60  are changed. In example 17, thicknesses of the first NiAl layer  40  and the second NiAl layer  60  were 0 nm (the first NiAl layer  40  and the second NiAl layer  60  were not included). In example 18, the thicknesses of the first NiAl layer  40  and the second NiAl layer  60  were each 0.42 nm. In example 19, the thicknesses of the first NiAl layer  40  and the second NiAl layer  60  were each 0.63 nm. In example 20, the thicknesses of the first NiAl layer  40  and the second NiAl layer  60  were each 0.84 nm. In example 21, the thicknesses of the first NiAl layer  40  and the second NiAl layer  60  were each 1.05 nm. 
     The results of MR ratios in examples 17 to 21 are shown in table 3 below. As shown in table 3, the magnetoresistance effect elements of examples 17 to 21 all had a higher MR ratio than the magnetoresistance effect elements of comparative examples 1 to 4. That is, in the magnetoresistance effect elements of examples 17 to 21, the MR ratio can be improved when a structure using the first NiAl layer  40  and the second NiAl layer  60  is employed, and it can be said that a state of the high MR ratio can be maintained even after they undergo the annealing treatment at 500° C. for 15 minutes, and it can be said that a state change of the Heusler alloy due to the annealing does not occur. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                   
                   
                 MR ratio 
                 NiAl thick- 
               
               
                   
                 Compositional formula 
                 (%) 
                 ness (nm) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Example 17 
                 Co 2 (Fe 0.9 Ta 0.1 ) 1.03 Ga 0.42 Ge 0.85   
                 25.8 
                 0 
               
               
                 Example 1 
                 Co 2 (Fe 0.9 Ta 0.1 ) 1.03 Ga 0.42 Ge 0.85   
                 30.2 
                 0.21 
               
               
                 Example 18 
                 Co 2 (Fe 0.9 Ta 0.1 ) 1.03 Ga 0.42 Ge 0.85   
                 31.7 
                 0.42 
               
               
                 Example 19 
                 Co 2 (Fe 0.9 Ta 0.1 ) 1.03 Ga 0.42 Ge 0.85   
                 30 
                 0.63 
               
               
                 Example 20 
                 Co 2 (Fe 0.9 Ta 0.1 ) 1.03 Ga 0.42 Ge 0.85   
                 23.5 
                 0.84 
               
               
                 Example 21 
                 Co 2 (Fe 0.9 Ta 0.1 ) 1.03 Ga 0.42 Ge 0.85   
                 20.9 
                 1.05 
               
               
                   
               
            
           
         
       
     
     EXPLANATION OF REFERENCES 
     
         
         
           
               101 ,  102 ,  103  Magnetoresistance effect element 
               10  Substrate 
               20  Underlayer 
               21  First underlayer 
               22  Second underlayer 
               23  Third underlayer 
               24  Fourth underlayer 
               30  First ferromagnetic layer 
               40  First NiAl layer 
               50  Non-magnetic layer 
               60  Second NiAl layer 
               70  Second ferromagnetic layer 
               80  Cap layer 
               201  Magnetic recording device 
               202 ,  203  Magnetic recording element 
               210  Magnetic head 
               220  Resistance measuring device 
               230  Power supply 
               240  Measurement unit 
               300  Spin current magnetization rotational element 
               400  Magnetic domain wall displacement type magnetic recording element 
               401  First ferromagnetic layer 
               402  Second ferromagnetic layer 
               403  Non-magnetic layer 
               404  First magnetization fixed layer 
               405  Second magnetization fixed layer 
               500  Magnetic strip device 
               510  Magnetic recording medium 
               511  Magnetic strip 
               511 A First magnetic domain 
               511 B Second magnetic domain 
               512  Underlayer 
               513  Substrate 
               520  Magnetic recording head 
               530  Pulse power supply 
               600  Magnetic domain wall movement type spatial light modulator 
               610  First magnetization fixed layer 
               620  Second magnetization fixed layer 
               630  Light modulation layer 
               631 ,  636  Overlapping region 
               632 ,  635  Initial magnetic domain region 
               633 ,  634  Magnetic domain change region 
               700  High-frequency device 
               701  Direct current (DC) power supply 
               702  Inductor 
               703  Capacitor 
               704  Output port 
               705 ,  706  Wiring 
             DW Magnetic domain wall