Patent Description:
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 <NUM> describes an example in which a Co<NUM>FeGa<NUM>Ge<NUM> alloy, which is a Heusler alloy, is used for a ferromagnetic layer of the GMR element. Heusler alloys have been studied as materials that have a high likelihood of achieving a spin polarization of <NUM>% at room temperature.

Storage elements using a magnetoresistance effect element (for example, an MRAM) store information by utilizing magnetization reversal of a ferromagnetic layer. High-frequency devices using a magnetoresistance effect element oscillate a high-frequency by utilizing precessional motion of magnetization of a ferromagnetic layer. Magnetic sensors read an external magnetic state by utilizing rotation of magnetization or oscillation of magnetization of a ferromagnetic layer. When a magnetization direction of a ferromagnetic layer is made to be easily changed (magnetization rotation or magnetization reversal becomes easy), an amount of energy required to drive the element decreases. A Heusler alloy has a smaller value of saturation magnetization compared to a CoFe alloy or the like, and a magnetization direction of the ferromagnetic layer changes easily. There is a demand for a magnetoresistance effect element and a Heusler alloy in which an amount of energy required to rotate magnetization can be further reduced.

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 an amount of energy required to rotate magnetization can be further reduced.

The inventors of the present disclosure have found that an amount of energy required to rotate magnetization of a ferromagnetic layer can be further reduced by substituting a portion of elements constituting a Heusler alloy with an element having a small magnetic moment. The present disclosure provides the following means in order to solve the above problems.

An amount of energy required to rotate magnetization of the ferromagnetic layer in such a magnetoresistance effect element can be further reduced.

Embodiments and examples of the present disclosure only form part of the present invention if the respective Heusler alloy satisfies the general expression and the conditions as set out in appended claim <NUM>.

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.

<FIG> is a cross-sectional view of the magnetoresistance effect element according to a first embodiment. <FIG> is a cross-sectional view of the magnetoresistance effect element <NUM> along a lamination direction of layers of the magnetoresistance effect element. The magnetoresistance effect element <NUM> includes underlayers <NUM>, a first ferromagnetic layer <NUM>, a first NiAl layer <NUM>, a non-magnetic layer <NUM>, a second NiAl layer <NUM>, a second ferromagnetic layer <NUM>, and a cap layer <NUM> on a substrate <NUM>. The non-magnetic layer <NUM> is positioned between the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM>. The first NiAl layer <NUM> is positioned between the first ferromagnetic layer <NUM> and the non-magnetic layer <NUM>. The second NiAl layer <NUM> is positioned between the non-magnetic layer <NUM> and the second ferromagnetic layer <NUM>.

The substrate <NUM> is a portion serving as a base of the magnetoresistance effect element <NUM>. It is preferable to use a highly flat material for the substrate <NUM>. The substrate <NUM> 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. A material contained in the substrate <NUM> 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 may be exemplified. 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 <NUM> differ depending on intended products. When a product is a magnetic random access memory (MRAM), the substrate <NUM> may be, for example, a Si substrate having a circuit structure. When a product is a magnetic head, the substrate <NUM> may be, for example, an AlTiC substrate that is easy to process.

The underlayers <NUM> are positioned between the substrate <NUM> and the first ferromagnetic layer <NUM>. The underlayers <NUM> may include, for example, a first underlayer <NUM>, a second underlayer <NUM>, and a third underlayer <NUM> in order from a position near the substrate <NUM>.

The first underlayer <NUM> is a buffer layer which alleviates a difference between a lattice constant of the substrate <NUM> and a lattice constant of the second underlayer <NUM>. A material of the first underlayer <NUM> may be either a conductive material or an insulating material. The material of the first underlayer <NUM> also differs depending on a material of the substrate <NUM> and a material of the second underlayer <NUM>, but may be, for example, a compound having a (<NUM>)-oriented NaCl structure. The compound having a 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 <NUM> may also be, for example, a (<NUM>)-oriented perovskite-based conductive oxide represented by a compositional formula of ABO<NUM>. 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 <NUM> is a seed layer that enhances crystalline properties of an upper layer laminated on the second underlayer <NUM>. The second underlayer <NUM> may contain, for example, at least one selected from the group consisting of MgO, TiN, and NiTa alloys. The second underlayer <NUM> 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 <NUM> is a buffer layer which alleviates a difference between a lattice constant of the second underlayer <NUM> and a lattice constant of the first ferromagnetic layer <NUM>. The third underlayer <NUM> 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 <NUM> 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 <NUM> may be a layer having, for example, a (<NUM>)-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 <NUM> 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 <NUM> function as buffer layers which alleviate a difference in lattice constants between the substrate <NUM> and the first ferromagnetic layer <NUM> and enhance crystalline properties of an upper layer formed on the underlayers <NUM>. The first underlayer <NUM>, the second underlayer <NUM>, and third underlayer <NUM> may be omitted. That is, the underlayers <NUM> may be omitted or may be one layer or two layers. Also, among the first underlayer <NUM>, the second underlayer <NUM>, and the third underlayer <NUM>, there may be layers formed of the same material. Also, the underlayers <NUM> are not limited to the three layers and may be four or more.

The first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM> are magnetic materials. The first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM> each have magnetization. The magnetoresistance effect element <NUM> outputs a change in a relative angle between magnetization of the first ferromagnetic layer <NUM> and magnetization of the second ferromagnetic layer <NUM> as a change in a resistance value.

Magnetization of the second ferromagnetic layer <NUM> is easier to move than magnetization of the first ferromagnetic layer <NUM>. When a predetermined external force is applied, a magnetization direction of the first ferromagnetic layer <NUM> does not change (is fixed) while a magnetization direction of the second ferromagnetic layer <NUM> changes. When the magnetization direction of the second ferromagnetic layer <NUM> changes with respect to the magnetization direction of the first ferromagnetic layer <NUM>, a resistance value of the magnetoresistance effect element <NUM> changes. In this case, the first ferromagnetic layer <NUM> may be called a magnetization fixed layer, and the second ferromagnetic layer <NUM> may be called a magnetization free layer. Hereinafter, a case in which the first ferromagnetic layer <NUM> is the magnetization fixed layer and the second ferromagnetic layer <NUM> 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 <NUM> and the magnetization of the second ferromagnetic layer <NUM> when a predetermined external force is applied is caused by a difference in coercivity between the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM>. For example, when a thickness of the second ferromagnetic layer <NUM> is made smaller than a thickness of the first ferromagnetic layer <NUM>, a coercivity of the second ferromagnetic layer <NUM> becomes smaller than a coercivity of the first ferromagnetic layer <NUM>. Also, for example, an antiferromagnetic layer may be provided on a surface of the first ferromagnetic layer <NUM> on a side opposite to the non-magnetic layer <NUM> with a spacer layer interposed therebetween. The first ferromagnetic layer <NUM>, 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 <NUM> and the antiferromagnetic layer are antiferromagnetically coupled, a coercivity of the first ferromagnetic layer <NUM> 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 <NUM> 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. The first ferromagnetic layer <NUM> is preferably Co-Fe or Co-Fe-B, for example. The first ferromagnetic layer <NUM> may be the same Heusler alloy as the second ferromagnetic layer <NUM> to be described below.

The second ferromagnetic layer <NUM> is a Heusler alloy. A Heusler alloy is a half metal in which electrons passing through the non-magnetic layer <NUM> have only up or down spins and which ideally exhibits a spin polarization of <NUM>%.

A ferromagnetic Heusler alloy represented by X<NUM>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<NUM>YZ has a crystal structure of any one of an L2<NUM> structure, a B2 structure, and an A2 structure. Compounds represented by the compositional formula X<NUM>YZ have properties of becoming increasingly crystalline in the order of L2<NUM> structure > B2 structure > A2 structure.

<FIG> illustrate examples of crystal structures of a Heusler alloy represented by the compositional formula of X<NUM>YZ, in which <FIG> is a crystal of a Heusler alloy having an L2<NUM> structure, <FIG> is a B2 structure derived from the L2<NUM> structure, and <FIG> is an A2 structure derived from the L2<NUM> structure. In the L2<NUM> 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 <NUM> ≤ α+β. α is the number of Fe elements when the number of Co elements is <NUM> in a state before substitution, and β is the number of Z elements when the number of Co elements is <NUM> in a state before substitution. In a state after substitution, for example, α is the number of Fe elements when the numbers of Co elements and substitution elements to be described below are <NUM>, and β is the number of Z elements to be described below when the numbers of Co elements and substitution elements to be described below are <NUM>. The Heusler alloy according to the present embodiment is out of a stoichiometric composition (α+β = <NUM>) of the Heusler alloy represented by X<NUM>YZ illustrated in <FIG>. For α+β, it is preferable that <NUM> ≤ α+β < <NUM>, and particularly preferable that <NUM> < α+β < <NUM>.

In the Heusler alloy according to the present embodiment, α and β satisfy a relationship of α < β. There are cases in which the Fe element is substituted with an element of the X element site. The substitution of the Fe element for the X element site is called anti site. 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 a magnetoresistance (MR) ratio of the magnetoresistance effect element <NUM>. For α and β, it is preferable that α < β <<NUM>×α, and particularly preferable that α < β <<NUM>×α. When β does not become too large with respect to α, disturbances in a crystal structure of the Heusler alloy can be suppressed, and a decrease in the MR ratio of the magnetoresistance effect element <NUM> can be suppressed.

Also, in the Heusler alloy according to the present embodiment, α satisfies a relationship of <NUM> < α <<NUM>. In order to suppress the antisite, for α, it is preferable that <NUM> < α < <NUM>, and particularly preferable that <NUM> < α < <NUM>.

Also, in the Heusler alloy according to the present embodiment, some elements of an alloy represented by Co<NUM>FeαZβ are substituted with a substitution element. The Z element is one or more elements selected from the group consisting of Mn, Cr, 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 Co element.

The substitution element is an element different from the Z element and has a smaller magnetic moment than Co. The substitution element may be, for example, one or more elements selected from the group consisting of Ni, Cu, Zn, Ru, Rh, Pd, Ag, Cd, Ir, Pt, and Au. Even when these elements are substituted with the Co element, a crystal structure thereof is easily maintained. Also, the substitution element is preferably one or more elements selected from the group consisting of Cu, Ag, and Au. A smaller magnitude of magnetic moment of a magnetic material per atom, which is obtained according to Hund's rule, corresponds to a smaller number of outermost shell valence electrons. When a portion of the Co element is substituted with one or more elements selected from the group consisting of Cu, Ag, and Au, the number of outermost shell valence electrons can be decreased and a saturation magnetization can be made small. When a saturation magnetization of a magnetic material is small, the magnetization is easily reversed.

The Heusler alloy according to the present embodiment may be represented by, for example, the following general expression (<NUM>).

(Co<NUM>-aX1a)<NUM>(Fe<NUM>-bY1b)αZβ.

In expression (<NUM>), X1 is a substitution element, and Y1 is one or more second substitution elements selected from the group consisting of elements having a smaller magnetic moment than Fe. a and b satisfy <NUM> < a <<NUM> and b ≥ <NUM>. In general expression (<NUM>), α is the number of elements of the Y site (Fe elements or the second substitution elements) when the number of elements of the X site (Co elements or the substitution elements) is <NUM>, and β is the number of Z elements when the number of elements of the X site is <NUM>.

The second substitution element may be the same as or different from the substitution element. The second substitution element is preferably one or more elements selected from the group consisting of elements having a melting point higher than that of Fe among elements of Groups <NUM> to <NUM> in the periodic table. When the Fe element is substituted with an element having a melting point higher than that of the Fe element, a melting point of the Heusler alloy can be increased. When a melting point of the Heusler alloy increases, element diffusion from the Heusler alloy into other layers can be suppressed, and a decrease in the MR ratio of the magnetoresistance effect element <NUM> can be suppressed.

Also, the Heusler alloy according to the present embodiment may be represented by, for example, the following general expression (<NUM>).

(Co<NUM>-aX1a)<NUM>FeαZβ.

In expression (<NUM>), X1 is a substitution element. a satisfies <NUM> < a < <NUM>. In general expression (<NUM>), α is the number of elements of the Y site (Fe elements or the second substitution elements) when the number of elements of the X site (Co elements or the substitution elements) is <NUM>, and β is the number of Z elements when the number of elements of the X site is <NUM>. General expression (<NUM>) is one in which the Fe element in general expression (<NUM>) is not substituted and corresponds to a case in which b = <NUM> in general expression (<NUM>).

(Co<NUM>-aX1a)<NUM>(Fe<NUM>-bY1b)α(Ga<NUM>-cZ1c)β.

In expression (<NUM>), X1 is a substitution element, Y1 is a second substitution element, and Z1 is one or more elements selected from the group consisting of Mn, Cr, Al, Si, Ge, and Sn. General expression (<NUM>) satisfies <NUM> < a < <NUM>, b ≥ <NUM>, and <NUM> ≤ β(<NUM>-c). General expression (<NUM>) corresponds to a case in which a portion of the Z element in general expression (<NUM>) is Ga.

Ga has a low melting point and performs ordering of the crystal structure of the Heusler alloy even at a low temperature. When the number of elements of the X site (Co elements or the substitution elements) is <NUM>, if Ga is contained in an amount of <NUM> or more, the Heusler alloy is easily ordered even at a low temperature. In the Heusler alloy of general expression (<NUM>), element diffusion of constituent elements thereof into other layers can be suppressed, and a decrease in the MR ratio of the magnetoresistance effect element <NUM> can be suppressed. Also, an abundance ratio of the Ga element is preferably smaller than an abundance ratio of the Z1 element. That is, it is preferable that c > <NUM> be satisfied. When too much Ga is contained in the Heusler alloy, a melting point of the Heusler alloy is lowered, and the Ga diffuses into other layers.

(Co<NUM>-aX1a)<NUM>(Fe<NUM>-bY1b)α(Ge<NUM>-dZ2d)β ···     (<NUM>).

In expression (<NUM>), X1 is a substitution element, Y1 is a second substitution element, and Z2 is one or more elements selected from the group consisting of Mn, Cr, Al, Si, Ga, and Sn. General expression (<NUM>) satisfies <NUM> < a <<NUM>, b ≥ <NUM>, and <NUM> ≤ β(<NUM>-d).

Ge is a semiconductor element and has an effect of increasing resistivity of the Heusler alloy. When the Heusler alloy contains Ge, a 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 <NUM> or more when the number of elements of X site (Co elements or the substitution elements) is <NUM>. An abundance ratio of the Ge element is preferably higher than an abundance ratio of the Z2 element. That is, it is preferable that d < <NUM> be satisfied. On the other hand, when the abundance ratio of the Ge element is too large, resistivity of the Heusler alloy increases and becomes a parasitic resistance component of the magnetoresistance effect element <NUM>. For β(<NUM>-d), it is more preferable that <NUM> < β(<NUM>-d) < <NUM>, and particularly preferable that <NUM> < β(<NUM>-d) < <NUM>.

Also, in general expression (<NUM>) described above, the Z2 element may be Ga. In this case, general expression (<NUM>) is represented by the following general expression (<NUM>).

(Co<NUM>-aX1a)<NUM>(Fe<NUM>-bY1b)α(Ge<NUM>-dGad)β ···     (<NUM>).

In expression (<NUM>), X1 is a substitution element, and Y1 is a second substitution element. General expression (<NUM>) satisfies <NUM> < a < <NUM>, b ≥ <NUM>, <NUM> ≤ β(<NUM>-d), and <NUM> ≤ βd.

The Heusler alloy of general expression (<NUM>) contains Ga and Ge as the Z element. In the Heusler alloy of general expression (<NUM>), characteristics as a half metal are enhanced due to a synergistic effect of Ga and Ge, and thus a spin polarization thereof is improved. The magnetoresistance effect element <NUM> using the Heusler alloy of general expression (<NUM>) is further increased in the MR ratio and the RA due to the above-described synergistic effect of Ga and Ge.

In general expression (<NUM>), 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 (<NUM>) satisfy <NUM> < β(<NUM>-d) < <NUM> and particularly preferable that it satisfy <NUM> < β(<NUM>-d) <<NUM>.

Also, in general expression (<NUM>) described above, the Z2 element may be Ga and Mn. In this case, general expression (<NUM>) is represented by the following general expression (<NUM>).

(Co<NUM>-aX1a)<NUM>(Fe<NUM>-bY1b)α(Ge<NUM>-dGaeMnf)β.

In expression (<NUM>), X1 is a substitution element and Y1 is a second substitution element. General expression (<NUM>) satisfies <NUM> < a < <NUM>, b ≥ <NUM>, e+f = d > <NUM>, <NUM> ≤ β(<NUM>-d), <NUM> ≤ βe, and <NUM> ≤ βf.

Mn has an effect of increasing the MR ratio of the magnetoresistance effect element <NUM> when it coexists with Ga and Ge. Even when the Mn element is substituted with an element of the X element site, half metal characteristics are not easily deteriorated. In general expression (<NUM>), 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(<NUM>-d) satisfy <NUM> < β(<NUM>-d) < <NUM>, βe satisfy <NUM> < βe <<NUM>, and βf satisfy <NUM> < βf < <NUM>. 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 <NUM> is further increased.

In the Heusler alloy according to the present embodiment, an amount of energy required to rotate magnetization can be reduced. Although the reason why an amount of energy required for magnetization rotation is reduced is not clear, it is considered that an amount of energy required for magnetization rotation is reduced by overlap of a plurality of factors below.

A first factor is that a composition of the Heusler alloy is out of the stoichiometric composition of α+β = <NUM>, and is <NUM> ≤ α+β. Thereby, density of states of minority spins in the Fermi energy decreases, and a damping constant becomes small. A damping constant is a physical quantity originating from a spin-orbit interaction. The damping constant is also called a magnetic friction coefficient or a magnetic relaxation coefficient, and when the damping constant is small, magnetization is easily moved (easily rotated) due to an external force such as a spin transfer torque.

A second factor is that a portion of the elements of the alloy is substituted with a substitution element having a smaller magnetic moment than Co. When it is substituted with a substitution element having the smaller magnetic moment than Co, magnetic anisotropy energy becomes smaller than that of the substance before the substitution. When the magnetic anisotropy energy of the Heusler alloy becomes small, magnetization is easily reversed.

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 L2<NUM> structure, peaks of (<NUM>) and (<NUM>) are shown, but when the Heusler alloy has the B2 structure, a (<NUM>) peak is shown but a (<NUM>) peak is not shown. For example, in a case of RHEED, when the Heusler alloy has the L2<NUM> structure, streaks of (<NUM>) and (<NUM>) are shown, but when the Heusler alloy has the B2 structure, a (<NUM>) streak is shown, but a (<NUM>) 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 <NUM>, 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 a film thickness of the Heusler alloy be set to about <NUM> to <NUM> although it depends on resolution of analytical instruments.

The first NiAl layer <NUM> and the second NiAl layer <NUM> are layers containing a NiAl alloy. The first NiAl layer <NUM> is a buffer layer that alleviates lattice mismatching between the first ferromagnetic layer <NUM> and the non-magnetic layer <NUM>. The second NiAl layer <NUM> is a buffer layer that alleviates lattice mismatching between the non-magnetic layer <NUM> and the second ferromagnetic layer <NUM>.

The first NiAl layer <NUM> and the second NiAl layer <NUM> each may have a thickness t of, for example, <NUM> < t ≤ <NUM>. When the thickness t is too large, there is a likelihood of spin scattering occurring in electrons moving from the first ferromagnetic layer <NUM> (the second ferromagnetic layer <NUM>) to the second ferromagnetic layer <NUM> (the first ferromagnetic layer <NUM>). 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 <NUM> and the non-magnetic layer <NUM> is reduced, and lattice mismatching between the non-magnetic layer <NUM> and the second ferromagnetic layer <NUM> is reduced. When the lattice mismatching between the layers is reduced, the MR ratio of the magnetoresistance effect element <NUM> is improved.

The non-magnetic layer <NUM> is made of a non-magnetic metal. A material of the non-magnetic layer <NUM> may be, for example, Cu, Au, Ag, Al, Cr, or the like. The non-magnetic layer <NUM> 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 <NUM>% or more in the compositional formula. The non-magnetic layer <NUM> 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 <NUM> using Ag is further increased.

The non-magnetic layer <NUM> may have a thickness in a range of, for example, <NUM> or more and <NUM> or less. The non-magnetic layer <NUM> hinders magnetic coupling between the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM>.

Also, the non-magnetic layer <NUM> may be an insulator or a semiconductor. The non-magnetic insulator may be, for example, a material such as Al<NUM>O<NUM>, SiO<NUM>, MgO, MgAl<NUM>O<NUM>, 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 <NUM> is formed of a non-magnetic insulator, the non-magnetic layer <NUM> is a tunnel barrier layer. The non-magnetic semiconductor may be, for example, Si, Ge, CuInSe<NUM>, CuGaSe<NUM>, Cu(In, Ga)Se<NUM>, or the like.

The cap layer <NUM> is positioned on a side of the magnetoresistance effect element <NUM> opposite to the substrate <NUM>. The cap layer <NUM> is provided to protect the second ferromagnetic layer <NUM>. The cap layer <NUM> suppresses diffusion of atoms from the second ferromagnetic layer <NUM>. Also, the cap layer <NUM> also contributes to crystal orientations of each layer of the magnetoresistance effect element <NUM>. When the cap layer <NUM> is provided, magnetizations of the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM> are stabilized, and the MR ratio of the magnetoresistance effect element <NUM> can be improved.

The cap layer <NUM> 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 <NUM> 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 <NUM> according to the present embodiment will be described. The magnetoresistance effect element <NUM> can be obtained by laminating, for example, the underlayers <NUM> (the first underlayer <NUM>, the second underlayer <NUM>, and the third underlayer <NUM>), the first ferromagnetic layer <NUM>, the first NiAl layer <NUM>, the non-magnetic layer <NUM>, the second NiAl layer <NUM>, the second ferromagnetic layer <NUM>, and the cap layer <NUM> on the substrate <NUM> 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 <NUM> may be annealed after forming the underlayers <NUM> or after laminating the second ferromagnetic layer <NUM>. The annealing enhances crystalline properties of each layer.

The laminate formed of the first ferromagnetic layer <NUM>, the non-magnetic layer <NUM>, and the second ferromagnetic layer <NUM> constituting the magnetoresistance effect element <NUM> 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 <NUM> according to the present embodiment uses the above-described Heusler alloy for at least one of the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM>. Magnetization of the above-described Heusler alloy is easily reversed, and thus a current density during operation of the magnetoresistance effect element <NUM> can be reduced.

<FIG> is a cross-sectional view of a magnetoresistance effect element according to a second embodiment. A magnetoresistance effect element <NUM> is different from the magnetoresistance effect element <NUM> illustrated in <FIG> in that the first NiAl layer <NUM> and the second NiAl layer <NUM> are not provided. In <FIG>, constituents the same as those in <FIG> will be denoted by the same references, and description thereof will be omitted.

In the magnetoresistance effect element <NUM> of the second embodiment, at least one of a first ferromagnetic layer <NUM> and a second ferromagnetic layer <NUM> is the Heusler alloy described above. The magnetoresistance effect element <NUM> of the second embodiment achieves the same effects as in the magnetoresistance effect element <NUM> of the first embodiment. Also, the magnetoresistance effect element <NUM> of the second embodiment does not include a first NiAl layer and a second NiAl layer, and the first ferromagnetic layer <NUM>, a non-magnetic layer <NUM>, and the second ferromagnetic layer <NUM> 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. The MR ratio is improved by directly sandwiching the non-magnetic layer <NUM> between the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM>. Also, layers exhibiting the magnetoresistance effect are three layers of the first ferromagnetic layer <NUM>, the second ferromagnetic layer <NUM>, and the non-magnetic layer <NUM>, and thus a total thickness of the magnetoresistance effect element <NUM> is reduced. When a thickness of one magnetoresistance effect element <NUM> 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 <NUM> and the second NiAl layer <NUM> are not required, a manufacturing process is simplified.

<FIG> is a cross-sectional view of a magnetoresistance effect element according to a third embodiment. A magnetoresistance effect element <NUM> is different from the magnetoresistance effect element <NUM> illustrated in <FIG> in that underlayers <NUM> include a fourth underlayer <NUM>. Therefore, in <FIG>, constituents the same as those in <FIG> will be denoted by the same references, and description thereof will be omitted.

The fourth underlayer <NUM> is disposed between a third underlayer <NUM> and a first ferromagnetic layer <NUM>. The fourth underlayer <NUM> functions as a seed layer that enhances crystalline properties of the first ferromagnetic layer <NUM> laminated on the underlayers <NUM>. The fourth underlayer <NUM> may be, for example, an alloy containing Co and Fe. When the first ferromagnetic layer <NUM> 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 <NUM>. In the magnetoresistance effect element <NUM> in which the alloy containing Co and Fe is used for the fourth underlayer <NUM>, since magnetization of the Heusler alloy forming the first ferromagnetic layer <NUM> is further stabilized, the 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.

The magnetoresistance effect elements <NUM>, <NUM>, and <NUM> according to the respective embodiments can be used for various applications. The magnetoresistance effect elements <NUM>, <NUM>, and <NUM> 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 <NUM> 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 <NUM> of the second embodiment and the magnetoresistance effect element <NUM> of the third embodiment are used.

<FIG> is a cross-sectional view of a magnetic recording device according to application example <NUM>. <FIG> is a cross-sectional view of the magnetoresistance effect element <NUM> along the lamination direction of the layers of the magnetoresistance effect element.

As illustrated in <FIG>, a magnetic recording device <NUM> includes a magnetic head <NUM> and a magnetic recording medium W. In <FIG>, 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 <NUM> and perpendicular to the XY plane is referred to as a Z direction.

The magnetic head <NUM> has an air bearing surface (air bearing surface, medium facing surface) S facing a surface of the magnetic recording medium W. The magnetic head <NUM> 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 <NUM> includes the magnetoresistance effect element <NUM> that acts as a magnetic sensor, and a magnetic recording unit (not illustrated). A resistance measuring device <NUM> is connected to the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM> of the magnetoresistance effect element <NUM>.

The magnetic recording unit applies a magnetic field to a recording layer W1 of the magnetic recording medium W and determines a magnetization direction of the recording layer W1. That is, the magnetic recording unit performs magnetic recording on the magnetic recording medium W. The magnetoresistance effect element <NUM> reads information of the magnetization of the recording layer W1 written by the magnetic recording unit.

The magnetic recording medium W includes the recording layer W1 and a backing layer W2. The recording layer W1 is a portion which performs magnetic recording, and the backing layer W2 is a magnetic path (magnetic flux passage) which recirculates a writing magnetic flux to the magnetic head <NUM> again. The recording layer W1 records magnetic information as a magnetization direction.

The second ferromagnetic layer <NUM> of the magnetoresistance effect element <NUM> is a magnetization free layer. Therefore, the second ferromagnetic layer <NUM> exposed on the air bearing surface S is affected by magnetization recorded in the facing recording layer W1 of the magnetic recording medium W. For example, in <FIG>, a magnetization direction of the second ferromagnetic layer <NUM> is oriented in a +z direction by being affected by magnetization of the recording layer W1 oriented in the +z direction. In this case, magnetization directions of the first ferromagnetic layer <NUM> which is a magnetization fixed layer and the second ferromagnetic layer <NUM> are parallel to each other.

The second ferromagnetic layer <NUM> of the magnetic head <NUM> is the Heusler alloy described above, and an amount of energy required for magnetization reversal is small. Therefore, the magnetic head <NUM> can read the magnetization recorded in the recording layer W1 with high sensitivity.

Here, resistance when magnetization directions of the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM> are parallel is different from resistance when magnetization directions of the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM> are antiparallel. Therefore, information on the magnetization of the recording layer W1 can be read as a change in resistance value by measuring resistances of the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM> using the resistance measuring device <NUM>.

A shape of the magnetoresistance effect element <NUM> of the magnetic head <NUM> 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 <NUM> of the magnetoresistance effect element <NUM>, the first ferromagnetic layer <NUM> may be installed at a position away from the magnetic recording medium W.

<FIG> is a cross-sectional view of a magnetic recording element according to application example <NUM>. <FIG> is a cross-sectional view of the magnetoresistance effect element <NUM> along the lamination direction of the layers of the magnetoresistance effect element.

As illustrated in <FIG>, a magnetic recording element <NUM> includes the magnetoresistance effect element <NUM>, a power supply <NUM> and a measurement unit <NUM> which are connected to the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM> of the magnetoresistance effect element <NUM>. When the third underlayer <NUM> of the underlayers <NUM> has conductivity, the power supply <NUM> and the measurement unit <NUM> may be connected to the third underlayer <NUM> instead of the first ferromagnetic layer <NUM>. Also, when the cap layer <NUM> has conductivity, the power supply <NUM> and the measurement unit <NUM> may be connected to the cap layer <NUM> instead of the second ferromagnetic layer <NUM>. The power supply <NUM> applies a potential difference to the magnetoresistance effect element <NUM> in the lamination direction. The measurement unit <NUM> measures a resistance value of the magnetoresistance effect element <NUM> in the lamination direction.

When a potential difference is generated between the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM> by the power supply <NUM>, a current flows in the lamination direction of the magnetoresistance effect element <NUM>. The current is spin-polarized during passing through the first ferromagnetic layer <NUM> and becomes a spin-polarized current. The spin-polarized current reaches the second ferromagnetic layer <NUM> via the non-magnetic layer <NUM>. Magnetization of the second ferromagnetic layer <NUM> receives a spin transfer torque (STT) due to the spin-polarized current, and the magnetization is reversed. The second ferromagnetic layer <NUM> is the Heusler alloy described above, and the magnetization is reversed with a small amount of energy. When a relative angle between a magnetization direction of the first ferromagnetic layer <NUM> and a magnetization direction of the second ferromagnetic layer <NUM> changes, a resistance value of the magnetoresistance effect element <NUM> in the lamination direction changes. The resistance value of the magnetoresistance effect element <NUM> in the lamination direction is read by the measurement unit <NUM>. That is, the magnetic recording element <NUM> illustrated in <FIG> is a spin transfer torque (STT) type magnetic recording element.

As illustrated in <FIG>, a magnetic recording element <NUM> includes the magnetoresistance effect element <NUM>, the power supply <NUM> connected to both ends of the third underlayer <NUM> of the magnetoresistance effect element <NUM>, and the measurement unit <NUM> connected to the third underlayer <NUM> and the second ferromagnetic layer <NUM>. The third underlayer <NUM> 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 <NUM> may be, for example, a layer containing a non-magnetic metal having an atomic number of <NUM> or higher having d electrons or f electrons in the outermost shell. Also, when the cap layer <NUM> has conductivity, the measurement unit <NUM> may be connected to the cap layer <NUM> instead of the second ferromagnetic layer <NUM>. The power supply <NUM> is connected to a first end and a second end of the third underlayer <NUM>. The power supply <NUM> applies a potential difference in an in-plane direction between one end portion (the first end) of the third underlayer <NUM> and an end portion (the second end) thereof on a side opposite to the first end. The measurement unit <NUM> measures a resistance value of the magnetoresistance effect element <NUM> in the lamination direction. In the magnetoresistance effect element <NUM> illustrated in <FIG>, the first ferromagnetic layer <NUM> is a magnetization free layer and the second ferromagnetic layer <NUM> is a magnetization fixed layer.

When a potential difference is generated between the first end and the second end of the third underlayer <NUM> by the power supply <NUM>, a current flows along the third underlayer <NUM>. When a current flows along the third underlayer <NUM>, 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 <NUM> and induces a spin current in a thickness direction of the third underlayer <NUM>. The spins are injected into the first ferromagnetic layer <NUM> from the third underlayer <NUM> by the spin current.

The spins injected into the first ferromagnetic layer <NUM> impart a spin-orbit torque (SOT) to magnetization of the first ferromagnetic layer <NUM>. The first ferromagnetic layer <NUM> receives the spin-orbit torque (SOT), and the magnetization is reversed. The first ferromagnetic layer <NUM> is the Heusler alloy described above, and the magnetization is reversed with a small amount of energy. When a magnetization direction of the first ferromagnetic layer <NUM> and a magnetization direction of the second ferromagnetic layer <NUM> change, a resistance value of the magnetoresistance effect element <NUM> in the lamination direction changes. The resistance value of the magnetoresistance effect element <NUM> in the lamination direction is read by the measurement unit <NUM>. That is, the magnetic recording element <NUM> illustrated in <FIG> is a spin-orbit torque (SOT) type magnetic recording element.

<FIG> is a cross-sectional view of a spin current magnetization rotational element according to application example <NUM>.

A spin current magnetization rotational element <NUM> is obtained by removing the first NiAl layer <NUM>, the non-magnetic layer <NUM>, the second NiAl layer <NUM>, the second ferromagnetic layer <NUM>, and the cap layer <NUM> from the magnetic recording element <NUM> illustrated in <FIG>. In the spin current magnetization rotational element <NUM>, the first ferromagnetic layer <NUM> is the Heusler alloy represented by general expression (<NUM>) described above.

When a potential difference is generated between the first end and the second end of the third underlayer <NUM> by the power supply <NUM>, a current flows along the third underlayer <NUM>. When a current flows along the third underlayer <NUM>, a spin Hall effect occurs due to a spin-orbit interaction. The spins injected from the third underlayer <NUM> impart a spin-orbit torque (SOT) to magnetization of the first ferromagnetic layer <NUM>. A magnetization direction of the first ferromagnetic layer <NUM> changes due to the spin-orbit torque (SOT).

When a magnetization direction of the first ferromagnetic layer <NUM> changes, polarization of reflected light changes due to a magnetic Kerr effect. Also, when a magnetization direction of the first ferromagnetic layer <NUM> changes, polarization of transmitted light changes due to a magnetic Faraday effect. The spin current magnetization rotational element <NUM> can be used as an optical element utilizing the magnetic Kerr effect or the magnetic Faraday effect.

<FIG> is a cross-sectional view of a magnetic domain wall movement element (magnetic domain wall displacement type magnetic recording element) according to application example <NUM>. A magnetic domain wall displacement type magnetic recording element <NUM> includes a first ferromagnetic layer <NUM>, a second ferromagnetic layer <NUM>, a non-magnetic layer <NUM>, a first magnetization fixed layer <NUM>, and a second magnetization fixed layer <NUM>. In <FIG>, a direction in which the first ferromagnetic layer <NUM> 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 <NUM> is sandwiched between the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM> in the Z direction. The first magnetization fixed layer <NUM> and the second magnetization fixed layer <NUM> are connected to the first ferromagnetic layer <NUM> at a position sandwiching the second ferromagnetic layer <NUM> and the non-magnetic layer <NUM> in the X direction.

The first ferromagnetic layer <NUM> is a layer in which information can be magnetically recorded according to a change in internal magnetic state. The first ferromagnetic layer <NUM> includes a first magnetic domain 401A and a second magnetic domain 401B therein. Magnetization of the first ferromagnetic layer <NUM> at a position overlapping the first magnetization fixed layer <NUM> or the second magnetization fixed layer <NUM> in the Z direction is fixed in one direction. Magnetization of the first ferromagnetic layer <NUM> at a position overlapping the first magnetization fixed layer <NUM> in the Z direction is fixed, for example, in a +Z direction, and magnetization of the first ferromagnetic layer <NUM> at a position overlapping the second magnetization fixed layer <NUM> 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 401A and the second magnetic domain 401B. The first ferromagnetic layer <NUM> can have the magnetic domain wall DW therein. In the first ferromagnetic layer <NUM> illustrated in <FIG>, a magnetization M401A of the first magnetic domain 401A is oriented in the +Z direction, and a magnetization M401B of the second magnetic domain 401B is oriented in the -Z direction.

The magnetic domain wall displacement type magnetic recording element <NUM> can record data in a multi-valued or consecutive manner by a position of the magnetic domain wall DW of the first ferromagnetic layer <NUM>. The data recorded in the first ferromagnetic layer <NUM> is read as a change in resistance value of the magnetic domain wall displacement type magnetic recording element <NUM> when a read current is applied.

Proportions of the first magnetic domain 401A and the second magnetic domain 401B in the first ferromagnetic layer <NUM> change when the magnetic domain wall DW moves. A magnetization M<NUM> of the second ferromagnetic layer <NUM> may be oriented, for example, in the same direction (parallel) as the magnetization M401A of the first magnetic domain 401A, and in an opposite direction (antiparallel) to the magnetization M401B of the second magnetic domain 401B. When the magnetic domain wall DW moves in the +X direction and an area of the first magnetic domain 401Ain a portion overlapping the second ferromagnetic layer <NUM> in a plan view from the z direction increases, a resistance value of the magnetic domain wall displacement type magnetic recording element <NUM> decreases. In contrast, when the magnetic domain wall DW moves in the -X direction and an area of the second magnetic domain 401B in a portion overlapping the second ferromagnetic layer <NUM> in a plan view from the Z direction increases, a resistance value of the magnetic domain wall displacement type magnetic recording element <NUM> increases.

The magnetic domain wall DW moves when a write current is caused to flow in the x direction of the first ferromagnetic layer <NUM> 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 <NUM> 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 401A toward the second magnetic domain 401B, electrons spin-polarized in the second magnetic domain 401B causes the magnetization M401A of the first magnetic domain 401A to be reversed. When the magnetization M401A of the first magnetic domain 401A is reversed, the magnetic domain wall DW moves in the -X direction.

As a material of the first ferromagnetic layer <NUM>, for example, the Heusler alloy described above may be used. Magnetization of the above-described Heusler alloy is easily reversed, and the magnetic domain wall DW can be moved with a small amount of energy.

Also, it is preferable that the magnetic domain wall displacement type magnetic recording element <NUM> have a high MR ratio and a high RA. When the MR ratio of the magnetic domain wall displacement type magnetic recording element <NUM> 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 <NUM> increases, and reliability of data is improved. Also, when an RA of the magnetic domain wall displacement type magnetic recording element <NUM> is large, data can be recorded more in an analog manner. The first ferromagnetic layer <NUM> is preferably the Heusler alloy that satisfies general expression (<NUM>).

The second ferromagnetic layer <NUM> can use, 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 can be exemplified. As a material of the second ferromagnetic layer <NUM>, the Heusler alloy described above may be used.

The non-magnetic layer <NUM> can use a material the same as that of the non-magnetic layer <NUM> described above. A material the same as that of the second ferromagnetic layer <NUM> can be used for the first magnetization fixed layer <NUM> and the second magnetization fixed layer <NUM>. The first magnetization fixed layer <NUM> and the second magnetization fixed layer <NUM> may have a SAF structure.

<FIG> is a perspective view of a magnetic domain wall movement element (magnetic strip device) according to application example <NUM>.

As illustrated in <FIG>, a magnetic strip device <NUM> includes a magnetic recording medium <NUM>, a magnetic recording head <NUM>, and a pulse power supply <NUM>. The magnetic recording head <NUM> is provided at a predetermined position above the magnetic recording medium <NUM>. The pulse power supply <NUM> is connected to the magnetic recording medium <NUM> so that a pulse current can be applied in an in-plane direction of the magnetic recording medium <NUM>. Further, in <FIG>, one direction in which the magnetic recording medium <NUM> 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 <NUM> includes a magnetic strip <NUM>, an underlayer <NUM>, and a substrate <NUM>. The underlayer <NUM> is laminated on the substrate <NUM>, and the magnetic strip <NUM> is laminated on the underlayer <NUM>. The magnetic strip <NUM> is formed in a strip shape having a length in the X direction larger than a width in the Y direction.

The magnetic strip <NUM> 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 <NUM> may include, for example, a first magnetic domain 511A and a second magnetic domain 511B. A magnetization M511B of the second magnetic domain 511B is oriented in a direction different from a magnetization M511A of the first magnetic domain 511A. A magnetic domain wall DW is formed between the first magnetic domain 511A and the second magnetic domain 511B. The second magnetic domain 511B is generated by the magnetic recording head <NUM>.

The magnetic strip device <NUM> performs data writing by changing a position of the second magnetic domain 511B of the magnetic strip <NUM> using a magnetic field or spin injection magnetization reversal generated by the magnetic recording head <NUM> while intermittently shifting and moving the magnetic domain wall DW of the magnetic strip <NUM> by a pulse current supplied from the pulse power supply <NUM>. The data written in the magnetic strip device <NUM> 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 <NUM> 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 <NUM>.

The Heusler alloy described above can be used as a material of the magnetic strip <NUM>. When the magnetic strip <NUM> is the Heusler alloy described above, an amount of energy required to move the magnetic domain wall DW can be reduced. Also, when the Heusler alloy satisfying general expression (<NUM>) is used for the magnetic strip <NUM>, an RA of the magnetic strip device <NUM> can be increased.

As a material of the underlayer <NUM>, ferrite, which is an oxide insulator, more specifically, soft ferrite is preferably used in at least a portion 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 <NUM> is concentrated thereon, the soft ferrite can efficiently form the second magnetic domain 511B. A material the same as that of the substrate <NUM> described above can be used for the substrate <NUM>.

<FIG> is a perspective view of a magnetic domain wall movement element (magnetic domain wall movement type spatial light modulator) according to application example <NUM>.

As illustrated in <FIG>, a magnetic domain wall movement type spatial light modulator <NUM> includes a first magnetization fixed layer <NUM>, a second magnetization fixed layer <NUM>, and a light modulation layer <NUM>. In <FIG>, one direction in which the light modulation layer <NUM> 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<NUM> of the first magnetization fixed layer <NUM> and a magnetization M<NUM> of the second magnetization fixed layer <NUM> are oriented in different directions. For example, the magnetization M<NUM> of the first magnetization fixed layer <NUM> may be oriented in a +Z direction, and the magnetization M<NUM> of the second magnetization fixed layer <NUM> may be oriented in a -Z direction.

The light modulation layer <NUM> can be divided into overlapping regions <NUM> and <NUM>, initial magnetic domain regions <NUM> and <NUM>, and magnetic domain change regions <NUM> and <NUM>.

The overlapping region <NUM> is a region overlapping the first magnetization fixed layer <NUM> in the Z direction, and the overlapping region <NUM> is a region overlapping the second magnetization fixed layer <NUM> in the Z direction. A magnetization M<NUM> of the overlapping region <NUM> is affected by a leakage magnetic field from the first magnetization fixed layer <NUM> and may be fixed, for example, in the +Z direction. A magnetization M<NUM> of the overlapping region <NUM> is affected by a leakage magnetic field from the second magnetization fixed layer <NUM> and may be fixed, for example, in the -Z direction.

The initial magnetic domain regions <NUM> and <NUM> are regions whose magnetizations are fixed in directions different from those of the overlapping regions <NUM> and <NUM> by being affected by leakage magnetic fields from the first magnetization fixed layer <NUM> and the second magnetization fixed layer <NUM>. A magnetization M<NUM> of the initial magnetic domain region <NUM> is affected by a leakage magnetic field from the first magnetization fixed layer <NUM> and may be fixed, for example, in the -Z direction. A magnetization M<NUM> of the initial magnetic domain region <NUM> is affected by a leakage magnetic field from the second magnetization fixed layer <NUM> and may be fixed, for example, in the +Z direction.

The magnetic domain change regions <NUM> and <NUM> are regions in which the magnetic domain wall DW can move. A magnetization M<NUM> of the magnetic domain change region <NUM> and a magnetization M<NUM> of the magnetic domain change region <NUM> are oriented in opposite directions with the magnetic domain wall DW sandwiched therebetween. The magnetization M<NUM> of the magnetic domain change region <NUM> is affected by the initial magnetic domain region <NUM> and may be oriented, for example, in the -Z direction. The magnetization M<NUM> of the magnetic domain change region <NUM> is affected by a leakage magnetic field of the initial magnetic domain region <NUM> and may be fixed, for example, in the +Z direction. A boundary between the magnetic domain change region <NUM> and the magnetic domain change region <NUM> 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 <NUM> or an external magnetic field is applied.

The magnetic domain wall movement type spatial light modulator <NUM> changes a 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 <NUM>, and a light L2 reflected by the light modulation layer <NUM> 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 <NUM> 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 <NUM>, the Heusler alloy described above can be used. Thereby, the magnetic domain wall DW can be moved with a small amount of energy. Also, when the Heusler alloy satisfying general expression (<NUM>) is used for the light modulation layer <NUM>, an RA of the magnetic domain wall movement type spatial light modulator <NUM> can be increased. As a result, a 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 <NUM> and the second magnetization fixed layer <NUM> can be used for the first magnetization fixed layer <NUM> and the second magnetization fixed layer <NUM>.

<FIG> is a perspective view of a high-frequency device according to application example <NUM>.

As illustrated in <FIG>, a high-frequency device <NUM> includes the magnetoresistance effect element <NUM>, a direct current (DC) power supply <NUM>, an inductor <NUM>, a capacitor <NUM>, an output port <NUM>, and wirings <NUM> and <NUM>.

The wiring <NUM> connects the magnetoresistance effect element <NUM> and the output port <NUM>. The wiring <NUM> branches from the wiring <NUM> and reaches the ground G via the inductor <NUM> and the DC power supply <NUM>. For the DC power supply <NUM>, the inductor <NUM>, and the capacitor <NUM>, known ones can be used. The inductor <NUM> cuts a high-frequency component of a current and passes an invariant component of the current. The capacitor <NUM> passes a high-frequency component of a current and cuts an invariant component of the current. The inductor <NUM> is disposed at a portion in which a flow of the high-frequency current is desired to be suppressed, and the capacitor <NUM> 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 <NUM>, magnetization of the second ferromagnetic layer <NUM> performs precessional motion. Magnetization of the second ferromagnetic layer <NUM> oscillates strongly when a frequency of a high-frequency current or a high-frequency magnetic field applied to the second ferromagnetic layer <NUM> is near a ferromagnetic resonance frequency of the second ferromagnetic layer <NUM>, and does not oscillate as much at a frequency away from the ferromagnetic resonance frequency of the second ferromagnetic layer <NUM>. This phenomenon is called a ferromagnetic resonance phenomenon.

A resistance value of the magnetoresistance effect element <NUM> changes according to an oscillation of the magnetization of the second ferromagnetic layer <NUM>. The DC power supply <NUM> applies a DC current to the magnetoresistance effect element <NUM>. The DC current flows in the lamination direction of the magnetoresistance effect element <NUM>. The DC current flows to the ground G through the wirings <NUM> and <NUM> and the magnetoresistance effect element <NUM>. A potential of the magnetoresistance effect element <NUM> changes according to Ohm's law. A high-frequency signal is output from the output port <NUM> according to a change in potential (change in resistance value) of the magnetoresistance effect element <NUM>.

The second ferromagnetic layer <NUM> is the Heusler alloy described above and magnetization thereof can be caused to perform precessional motion with a small amount of energy. Also, the above-described Heusler alloy has a small saturation magnetization, and a Q value of the high-frequency device <NUM> is improved. The Q value is an index indicating sharpness of local maximum characteristics of a high-frequency signal. As the Q value increases, a high-frequency signal with a specific frequency is oscillated.

The magnetoresistance effect element <NUM> illustrated in <FIG> was fabricated as below. A configuration of each layer was as follows.

The first underlayer <NUM> (MgO layer) was deposited by heating the substrate <NUM> to <NUM> and using a sputtering method. The substrate on which the first underlayer <NUM> was deposited was held at <NUM> for <NUM> minutes and then allowed to be cooled to room temperature. Next, the second underlayer <NUM> (CoFe layer) was deposited on the first underlayer <NUM> using a sputtering method. Next, the third underlayer <NUM> (Ag layer) was deposited on the second underlayer <NUM> using a sputtering method, and thereby the underlayers <NUM> were formed. The substrate <NUM> on which the underlayers <NUM> were deposited was annealed at <NUM> for <NUM> minutes and then allowed to be cooled to room temperature.

After allowing it to be cooled, the first ferromagnetic layer <NUM> ((Co<NUM>Cu<NUM>)<NUM>Fe<NUM>Ga<NUM>) was deposited on the underlayers <NUM> formed on the substrate <NUM>. The deposition of the first ferromagnetic layer <NUM> was performed by a co-sputtering method using a Co-Fe-Ga alloy target and a Cu target as the targets.

The first NiAl layer <NUM> was deposited on the first ferromagnetic layer <NUM> using a sputtering method. Next, the non-magnetic layer <NUM> (Ag layer) was deposited on the first NiAl layer <NUM> using a sputtering method. Next, the second NiAl layer <NUM> was deposited on the non-magnetic layer <NUM> in the same manner as the first NiAl layer <NUM>. Then, the second ferromagnetic layer <NUM> ((Co<NUM>Cu<NUM>)<NUM>Fe<NUM>Ga<NUM>) was deposited on the second NiAl layer <NUM> in the same manner as the first ferromagnetic layer <NUM>. The substrate <NUM> on which the second ferromagnetic layer <NUM> was formed was annealed at <NUM> for <NUM> minutes, and then allowed to be cooled to room temperature.

After allowing it to be cooled, the cap layer <NUM> (Ru layer) was deposited on the second ferromagnetic layer <NUM> formed on the substrate <NUM> using a sputtering method. In this way, the magnetoresistance effect element <NUM> illustrated in <FIG> was fabricated.

Further, thin film compositions of the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM> 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.

A current was caused to flow in the lamination direction of the fabricated magnetoresistance effect element <NUM>, and a current density (inversion current density) required to change a magnetization direction of the second ferromagnetic layer <NUM> was obtained. The change in magnetization direction of the second ferromagnetic layer <NUM> was ascertained by monitoring a change in resistance value of the magnetoresistance effect element <NUM>.

An MR ratio of the fabricated magnetoresistance effect element <NUM> was also measured. As for the MR ratio, a change in resistance value of the magnetoresistance effect element <NUM> was measured by monitoring a voltage applied to the magnetoresistance effect element <NUM> with a voltmeter while sweeping a magnetic field from the outside to the magnetoresistance effect element <NUM> in a state in which a constant current is caused to flow in the lamination direction of the magnetoresistance effect element <NUM>. A resistance value when magnetization directions of the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM> are parallel and a resistance value when magnetization directions of the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM> 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 <NUM> (room temperature).

RP is a resistance value when magnetization directions of the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM> are parallel, and RAP is a resistance value when magnetization directions of the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM> are antiparallel.

Examples <NUM> to <NUM> are different from example <NUM> in that a substitution element that is substituted with the Co element is changed in the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM>. In example <NUM>, (Co<NUM>Ru<NUM>)<NUM>Fe<NUM>Ga<NUM> was used for the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM>. In example <NUM>, (Co<NUM>Rh<NUM>)<NUM>Fe<NUM>Ga<NUM> was used for the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM>. In example <NUM>, (Co<NUM>Pd<NUM>)<NUM>Fe<NUM>Ga<NUM> was used for the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM>. In example <NUM>, (Co<NUM>Ag<NUM>)<NUM>Fe<NUM>Ga<NUM> was used for the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM>.

Examples <NUM> to <NUM> are different from example <NUM> in that a ratio of the substitution element that is substituted with the Co element is changed in the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM>. In example <NUM>, (Co<NUM>Cu<NUM>)<NUM>Fe<NUM>Ga<NUM> was used for the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM>. In example <NUM>, (Co<NUM>Cu<NUM>)<NUM>Fe<NUM>Ga<NUM> was used for the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM>. In example <NUM>, (Co<NUM>Cu<NUM>)<NUM>Fe<NUM>Ga<NUM> was used for the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM>.

Examples <NUM> and <NUM> are different from example <NUM> in that a portion of the Fe element is substituted in the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM>. In example <NUM>, (Co<NUM>Cu<NUM>)<NUM>Fe<NUM>Hf<NUM>Ga<NUM> was used for the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM>. In example <NUM>, (Co<NUM>Cu<NUM>)<NUM>Fe<NUM>Ta<NUM>Ga<NUM> was used for the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM>.

Examples <NUM> and <NUM> are different from example <NUM> in that a portion of the Ga element is substituted with a different element in the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM>. In example <NUM>, (Co<NUM>Cu<NUM>)<NUM>Fe<NUM>Ga<NUM>Ge<NUM> was used for the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM>. In example <NUM>, (Co<NUM>Cu<NUM>)<NUM>Fe<NUM>Ga<NUM>Ge<NUM>Mn<NUM> was used for the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM>.

Comparative example <NUM> is different from example <NUM> in that the Co element is not substituted in the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM>. In comparative example <NUM>, Co<NUM>Fe<NUM>Ga<NUM> was used for the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM>.

Comparative example <NUM> is different from example <NUM> in composition ratio of each element in the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM>. In comparative example <NUM>, (Co<NUM>Cu<NUM>)<NUM>Fe<NUM>Ga<NUM> was used for the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM>.

Comparative example <NUM> is different from example <NUM> in that a composition ratio of each element is changed and the Co element is not substituted in the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM>. In comparative example <NUM>, Co<NUM>Fe<NUM>Ga<NUM> was used for the first ferromagnetic layer <NUM> and the second ferromagnetic layer <NUM>.

The measurement results of inversion current densities and MR ratios of examples <NUM> to <NUM> and comparative examples <NUM> to <NUM> are shown in Table <NUM> below. As shown in Table <NUM>, all of the magnetoresistance effect elements of examples <NUM> to <NUM> had lower inversion current densities compared to the magnetoresistance effect elements of comparative examples <NUM> to <NUM>.

Claim 1:
A Heusler alloy in which a portion of elements of an alloy is represented by the general expression (Co<NUM>-aX1a)<NUM>(Fe<NUM>-bY1b)αZβ, characterized in that,
Z is one or more elements selected from the group consisting of Mn, Cr, Al, Si, Ga, Ge, and Sn,
α and β satisfy <NUM> ≤ α+β, α < β, and <NUM> < α <<NUM>, and wherein
X1 is a substitution element, which is different from the Z element and has a smaller magnetic moment than Co,
Y1 is one or more second substitution elements selected from the group consisting of elements having a smaller magnetic moment than Fe, and
<NUM> < a < <NUM> and b ≥ <NUM> are satisfied.