JP7124788B2 - Spin current magnetization rotation type magnetoresistive effect element and magnetic memory - Google Patents

Description

The present invention relates to a spin current rotation magnetization magnetoresistance effect element and a magnetic memory.

A giant magnetoresistive (GMR) element consisting of a multilayer film of a ferromagnetic layer and a non-magnetic layer as an element that utilizes a change in resistance value (magnetoresistive change) based on a change in the relative angle of magnetization of two ferromagnetic layers, and A tunnel magnetoresistive (TMR) element using an insulating layer (tunnel barrier layer, barrier layer) as a non-magnetic layer is known.

In recent years, among spin devices using magnetoresistance change (devices using spintronics), spin current magnetization rotation type magnetoresistive effect devices using spin orbit torque (SOT) and domain wall displacement type magnetic devices using domain wall displacement have been developed. Attention is focused on recording elements.

For example, Non-Patent Document 1 describes a spin current magnetization rotating magnetoresistive element. SOT is induced by a pure spin current caused by spin-orbit interaction or by the Rashba effect at the interface of dissimilar materials. A current for inducing SOT in the spin current rotation magnetization magnetoresistive element flows in a direction intersecting with the stacking direction of the spin current rotation magnetization magnetoresistive element. The spin current rotation magnetization magnetoresistive effect element does not require a current to flow in the lamination direction, and is expected to have a longer life.

U.S. Pat. No. 8,963,222 Japanese Patent Application Laid-Open No. 2018-67701

S. Fukami, T.; Anekawa, C.; Zhang and H. Ohno, Nature NanoTec (2016). DOI: 10.1038/NNA NO. 2016.29. S. Takahashi and S.; Maekawa, Phys. Rev. B67(5), 052409 (2003).

A tunneling magnetoresistive element (SOT-MTJ) using SOT applies a current to the spin-orbit torque wiring layer to generate a spin current in a direction orthogonal to the current, thereby generating a first magnetic field in contact with the spin-orbit torque wiring layer. Invert the magnetization of the ferromagnetic layer. In Non-Patent Document 1, the direction in which the spin orbit torque wiring layer extends and the current flows is the X direction, the direction perpendicular to the X direction in the plane of the laminated film is the Y direction, and the direction perpendicular to the laminated film plane is the Z direction. and A spin current is generated when a current is passed in the X direction of the spin-orbit torque wiring layer. Spins reaching the interface between the spin-orbit torque wiring layer and the first ferromagnetic layer due to the spin current are oriented in the Y direction. When the magnetization direction of the first ferromagnetic layer is in the Y direction, the direction of spins injected into the first ferromagnetic layer is in the Y direction. do. When the magnetization direction of the first ferromagnetic layer is in the X direction or the Z direction, a magnetic field having components orthogonal to the magnetization direction and the direction of the spins constituting the spin current is applied to the first ferromagnetic layer. By doing so, the magnetization of the first ferromagnetic layer is reversed. It is known that a magnetic field affects magnetization reversal regardless of the direction of magnetization of the first ferromagnetic layer. In particular, when the magnetization direction of the first ferromagnetic layer is in the X direction or Z direction, even a slight magnetic field assists the magnetization reversal of the first ferromagnetic layer. in short. A magnetic field affects the magnetization reversal of the first ferromagnetic layer.

A magnetic memory is, for example, an integrated SOT-MTJ. The magnetization direction of the magnetization free layer carrying data of the SOT-MTJ is reversed each time data is rewritten. At this time, a magnetic field is generated from the magnetization free layer, and the generated magnetic field is applied to another adjacent SOT-MTJ. Therefore, in the integrated SOT-MTJ magnetic memory, the magnetic field from the adjacent SOT-MTJ cannot be ignored, and there is a problem that the magnetization reversal probability changes and data is rewritten.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a spin current rotating magnetization magnetoresistive element capable of suppressing the generation of a magnetic field that affects other elements.

In order to solve the above problems, the following means are provided.
A spin current rotation magnetization magnetoresistance effect element according to a first aspect includes a spin-orbit torque wiring layer, a first ferromagnetic layer, an antiferromagnetic coupling layer, a second ferromagnetic layer, a nonmagnetic layer, and a magnetization reference layer in this order, and the magnitude of the product of the saturation magnetization of the first ferromagnetic layer and the film thickness of the first ferromagnetic layer is larger than the product of film thicknesses.

The SOT-MTJ element according to the first aspect cancels the magnetic field generated from the second ferromagnetic layer by the magnetic field generated from the first ferromagnetic layer in the element. That is, the magnetic field generated from the first ferromagnetic layer and the magnetic field generated from the second ferromagnetic layer are in a mutually weakening relationship. As a result, the magnetic field emitted from the SOT-MTJ is weakened, and the influence of magnetic field application on adjacent SOT-MTJs is suppressed. Further, by making the product of the saturation magnetization of the first ferromagnetic layer and its film thickness larger than the product of the saturation magnetization of the second ferromagnetic layer and its film thickness, the influence of the magnetic flux on the magnetization reference layer is suppressed. , it is possible to reduce fluctuations in the magnetization of the magnetization reference layer. Thereby, the magnetization direction of the magnetization reference layer is stabilized regardless of the magnetization direction of the second ferromagnetic layer, and the magnetization can be maintained.

The first ferromagnetic layer preferably has a lower spin resistance than the second ferromagnetic layer. The spin current tends to flow in the direction where the spin resistance is low. The concentration of the spin current in the first ferromagnetic layer facilitates the magnetization reversal of the first ferromagnetic layer.

It is preferable that the first surface of the first ferromagnetic layer located on the spin orbit torque wiring layer has a larger area than the second surface of the second ferromagnetic layer located on the non-magnetic layer side. The larger the area of the first ferromagnetic layer, the larger the volume, and the stronger the ability to retain data.

The first ferromagnetic layer preferably contains an alloy containing at least one element selected from the group consisting of Co, Fe and Ni and at least one rare earth element. The spin diffusion length of the first ferromagnetic layer is shortened, the spin current generated from the spin-orbit torque wiring layer is absorbed by the first ferromagnetic layer, it becomes difficult to reach the second ferromagnetic layer, and the desired magnetization reversal occurs. easier to do. When the spin current reaches the second ferromagnetic layer, the direction of magnetization is opposite to the direction of magnetization of the first ferromagnetic layer, so it works to suppress magnetization reversal.

The first ferromagnetic layer preferably contains CoPt alloy, FePt alloy, CoPd alloy, FePd alloy, CoCrPt alloy, HoFe alloy, or SmFe alloy. Since these materials have strong magnetocrystalline anisotropy, data can be stably retained even if the size of the spin current rotating magnetization magnetoresistance effect element is reduced.

The thickness of the first ferromagnetic layer is preferably thinner than the thickness of the second ferromagnetic layer. Increasing the thickness of the second ferromagnetic layer increases the magnetoresistance ratio of the SOT-MTJ. Also, by increasing the thickness of the second ferromagnetic layer, the magnetization reference layer is less susceptible to the magnetization of the first ferromagnetic layer.

The non-magnetic layer is preferably made of a material having a spinel crystal structure. The durability of the SOT-MTJ is increased when a write current is applied to the spin-orbit torque wiring layer. Even if the SOT-MTJ is applied for a long period of time or a strong load is applied, the SOT-MTJ is less likely to fail.

A magnetic memory according to a second aspect has a plurality of spin current rotation magnetization magnetoresistive elements. This magnetic memory can be written at high speed, and can replace the SRAM with a nonvolatile high speed memory. By making the data nonvolatile, the standby power can be reduced to zero, and the power consumption of the magnetic memory (integrated device) can be reduced.

In the magnetic memory according to the above aspect, the easy axis directions of magnetization of the first ferromagnetic layer and the second ferromagnetic layer constituting the first spin current rotation magnetization magnetoresistance effect element are the first direction, and the first A direction connecting the spin current rotation magnetization type magnetoresistive element and the closest second spin current rotation magnetization type magnetoresistive element may be different from the first direction. It is less likely to be affected by the closest element, and changes in magnetization reversal probability and data retention can be suppressed.

According to the present invention, it is possible to provide a spin current rotation magnetization magnetoresistive element capable of suppressing the generation of a magnetic field that affects other elements.

FIG. 2 is a schematic diagram showing the laminated structure of the spin current rotating magnetization magnetoresistance effect element 100 according to the first embodiment. FIG. 10 is a schematic diagram showing a laminated structure of a spin current rotating magnetization magnetoresistance effect element 200 according to a second embodiment. FIG. 11 is a schematic diagram showing a laminated structure of a spin current rotating magnetization magnetoresistance effect element 300 according to a third embodiment. FIG. 2 is a schematic diagram showing the laminated structure of the magnetic recording layer 11 when the magnetization vector 2A of the first ferromagnetic layer 2 is larger than the magnetization vector 3A of the second ferromagnetic layer 3; FIG. 3 is a schematic diagram showing the lamination structure of the magnetic recording layer 11 when the magnetization vector 3A of the second ferromagnetic layer 3 is larger than the magnetization vector 2A of the first ferromagnetic layer 2; FIG. 11 is a schematic diagram showing a laminated structure of a spin current rotating magnetization magnetoresistance effect element 400 according to a fourth embodiment. FIG. 11 is a layout diagram of a magnetic memory according to layout example 1. FIG. FIG. 2 is a diagram showing a peripheral structure (including a write transistor and a select transistor) of a spin current rotation magnetization type magnetoresistive effect element; It shows a patchwork arrangement of the spin current rotation magnetization magnetoresistive effect element 100 in Type-X. A patchwork arrangement of the spin current rotation magnetization magnetoresistive effect element 100 in Type-Y is shown.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and overlapping descriptions are omitted. Up, down, left, and right refer to the positional relationship in the drawing.

(First embodiment)
Hereinafter, as the spin current rotating magnetization magnetoresistance effect element 100 according to the first embodiment, a form in which the magnetization reference layer 6 is composed of the simplest single layer will be described. It is assumed that the magnetic flux from the magnetization reference layer 6 is sufficiently small, and that only the magnetic flux generated from the magnetic recording layer 11 should be considered. The orientation direction of the magnetization of the magnetization reference layer 6 is less likely to change than the magnetization of the magnetic recording layer 11 when a predetermined external force is applied. The magnetic recording layer 11 is also called a magnetization free layer.

(Basic structure)
The spin current rotation magnetization magnetoresistance effect element 100 includes a spin-orbit torque wiring layer 1, a first ferromagnetic layer 2, an antiferromagnetic coupling layer 4, a second ferromagnetic layer 3, a nonmagnetic layer 5, and a magnetization reference layer 6. It is a structure in which they are stacked in order in the Z direction. The spin-orbit torque wiring layer 1 extends within the XY plane. The spin-orbit torque wiring layer 1 extends, for example, in the X direction. The layers above the first ferromagnetic layer 2 have a constricted structure with distance from the spin-orbit torque interconnection layer 1 . That is, the first ferromagnetic layer 2, the antiferromagnetic coupling layer 4, the second ferromagnetic layer 3, the nonmagnetic layer 5, and the magnetization reference layer 6 have an outer peripheral length or an outer diameter of It's getting smaller.
<Magnetic recording layer (magnetization free layer)>
The magnetic recording layer 11 has a first ferromagnetic layer 2 , a second ferromagnetic layer 3 and an antiferromagnetic coupling layer 4 . The first ferromagnetic layer 2 and the second ferromagnetic layer 3 are antiferromagnetically coupled by the antiferromagnetic coupling layer 4 . The magnetic flux generated from each of the first ferromagnetic layer 2 and the second ferromagnetic layer 3 forms a loop connecting the first ferromagnetic layer 2 and the second ferromagnetic layer 3 . The magnetization vector 11A of the entire magnetic recording layer 11 is the difference between the magnetization vector 2A of the first ferromagnetic layer 2 and the magnetization vector 3A of the second ferromagnetic layer 3 (see FIGS. 4A and 4B). By adjusting the film thickness and material of each of the first ferromagnetic layer 2 and the second ferromagnetic layer 3, the magnetic flux generated from substantially one magnetic recording layer 11 toward the outside can be brought close to zero.

If the magnetic field from the first ferromagnetic layer 2 and the magnetic field from the second ferromagnetic layer 3 are in a relationship of weakening each other, the magnetic field emitted from one spin current rotating magnetization magnetoresistive element 100 is weakened. That is, it is possible to suppress the influence of the magnetic field generated by one spin current rotation magnetization magnetoresistive element 100 on other adjacent spin current rotation magnetization magnetoresistive elements. If the product of the saturation magnetization of the first ferromagnetic layer 2 and its film thickness is made larger than the product of the saturation magnetization of the second ferromagnetic layer 3 and its film thickness, the magnetization reference layer 6 will The influence of magnetic flux can be suppressed. When the influence of the magnetic flux on the magnetization reference layer 6 becomes smaller, it becomes possible to reduce the magnetization fluctuation of the magnetization reference layer 6 . As a result, regardless of the magnetization direction of the second ferromagnetic layer 3, the magnetization direction of the magnetization reference layer 6 is stabilized, and data can be held stably.

A ferromagnetic material, especially a soft magnetic material, can be applied to the first ferromagnetic layer 2 and the second ferromagnetic layer 3 . For example, metals selected from the group consisting of Cr, Mn, Co, Fe and Ni, alloys containing one or more of these metals, and these metals and at least one or more elements of B, C, and N can be used for the first ferromagnetic layer 2 and the second ferromagnetic layer 3. The first ferromagnetic layer 2 and the second ferromagnetic layer 3 preferably contain an alloy containing at least one element selected from Co, Fe and Ni and at least one rare earth element. The first ferromagnetic layer 2 and the second ferromagnetic layer 3 contain, for example, CoPt alloy, FePt alloy, CoPd alloy, FePd alloy, CoCrPt alloy, HoFe alloy, or SmFe alloy. The first ferromagnetic layer 2 and the second ferromagnetic layer 3 are, for example, Co--Fe, Co--Fe--B, Ni--Fe, Co--Pt, Fe--Pt, Co--Pt, Fe--Pt, Co--Cr -Pt, Sm-Fe, Ho-Fe.

Also, the first ferromagnetic layer 2 may be a Heusler alloy. Heusler alloys have high spin polarizability, resulting in higher power output. Heusler alloys include intermetallic compounds with chemical compositions of XYZ or _X2YZ . X is a Co, Fe, Ni, or Cu group transition metal element or noble metal element on the periodic table, Y is a Mn, V, Cr, or Ti group transition metal or an element type X, and Z is , are typical elements of the III to V groups. Heusler alloys are, for example, _Co2FeSi , _Co2FeGe , _Co2FeGa , _Co2MnSi , _{Co2Mn1 - aFeaAlbSi1 - b} , _{Co2FeGe1 - cGac} .

<Spin-orbit torque wiring layer>
The spin-orbit torque wiring layer 1 extends in the XY plane. The spin-orbit torque wiring layer 1 is connected to one surface of the first ferromagnetic layer 2 in the Z direction, for example. The spin-orbit torque wiring layer 1 may be directly connected to the first ferromagnetic layer 2, or may be connected via another layer.

The spin-orbit torque wiring layer 1 is made of, for example, a material that generates a pure spin current by the spin Hall effect when current flows. As such a material, it is sufficient if it has a structure in which a pure spin current is generated in the spin orbit torque wiring layer 1 . Therefore, the material is not limited to a material composed of a single element, and may be composed of a portion composed of a material that easily generates a pure spin current and a portion composed of a material that hardly generates a pure spin current.

The spin Hall effect is a phenomenon in which a spin current is induced in a direction orthogonal to the direction of current based on spin-orbit interaction when a current is passed. The mechanism by which a spin current is generated by the spin Hall effect will be explained.

For example, when a potential difference is applied to both ends of the spin-orbit torque wiring layer 1 in the X direction, current flows along the X direction. When a current flows, the first spins S1 oriented in the Y direction and the second spins S2 oriented in the −Y direction are bent in a direction (Z direction) perpendicular to the current. For example, the traveling direction of the first spin S1 is bent in the +Z direction, and the traveling direction of the second spin S2 is bent in the -Z direction. The common Hall effect and the spin Hall effect are common in that the moving (moving) charges (electrons) can bend the moving (moving) direction. On the other hand, in the normal Hall effect, charged particles moving in a magnetic field are subjected to the Lorentz force and the direction of motion is bent. only flows), the difference is that the direction of spin movement is bent.

A non-magnetic material (a material that is not a ferromagnetic material) has the same number of electrons of the first spin S1 and the number of electrons of the second spin S2. That is, the number of electrons of the first spin S1 directed upward (+Z direction) is equal to the number of electrons of the second spin S2 directed downward (−Z direction). So the current as a net flow of charge is zero. A spin current without this electric current is particularly called a pure spin current.

It is the same in that the first spin S1 and the second spin S2 are bent in opposite directions when a current is passed through the ferromagnetic material. On the other hand, in a ferromagnetic material, either the first spin S1 or the second spin S2 is in a large state, and as a result, a net flow of charges occurs (a voltage is generated). Therefore, the material of the spin-orbit torque wiring layer 1 does not include a material consisting only of a ferromagnetic material.

Here, if the electron flow of the first spin S1 is J _↑ , the electron flow of the second spin S2 is J _↓ , and the spin current is J _S , then J _S =J _↑ −J _↓ . The pure spin current J _S flows in the Z direction in the figure. where J _S is the electron flow with 100% polarizability. In FIG. 1, when the first ferromagnetic layer 2 is brought into contact with the upper surface of the spin-orbit torque wiring layer 1, the pure spin current diffuses and flows into the ferromagnetic material. That is, spins are injected into the first ferromagnetic layer 2 .

The spin-orbit torque wiring layer 1 is made of any of metals, alloys, intermetallic compounds, metal borides, metal carbides, metal silicides, and metal phosphides that have the function of generating a pure spin current by the spin Hall effect when current flows. or

A main component of the spin-orbit torque wiring layer 1 is preferably a non-magnetic heavy metal. Here, heavy metal means a metal having a specific gravity higher than that of yttrium. The non-magnetic heavy metal is preferably a non-magnetic metal having an atomic number of 39 or higher and having d-electrons or f-electrons in the outermost shell. The spin-orbit torque wiring layer 1 is Hf, Ta, W, for example. These non-magnetic metals have a large spin-orbit interaction that causes the spin Hall effect.

Normally, when a current is passed through a metal, all electrons move in the opposite direction, regardless of their spin orientation. In contrast, non-magnetic metals with a large atomic number and d or f electrons in the outermost shell have a strong spin-orbit interaction, a strong spin-Hall effect, and the direction of electron movement depends on the electron spin direction. do. As a result, these non-magnetic metals tend to generate a pure spin current _Js .

The spin-orbit torque wiring layer 1 may also contain a magnetic metal. A magnetic metal refers to a ferromagnetic metal or an antiferromagnetic metal. If a trace amount of magnetic metal is contained in non-magnetic metal, it becomes a spin scattering factor. Scattering of spins enhances the spin-orbit interaction, increasing the efficiency of spin current generation with respect to electric current. The main component of the spin-orbit torque wiring layer 1 may consist only of an antiferromagnetic metal.

On the other hand, if the amount of the magnetic metal added is too large, the generated pure spin current may be scattered by the added magnetic metal, and as a result the effect of reducing the spin current may become stronger. Therefore, the molar ratio of the added magnetic metal is preferably sufficiently smaller than the total molar ratio of the elements forming the spin-orbit torque interconnection layer. As a guideline, the molar ratio of the magnetic metal to be added is preferably 3% or less.

Also, the spin-orbit torque wiring layer 1 may include a topological insulator. A main component of the spin-orbit torque wiring layer 1 may be a topological insulator. A topological insulator is a material whose interior is an insulator or a high resistance material, but whose surface has a spin-polarized metallic state. A topological insulator generates an internal magnetic field due to spin-orbit interaction. In topological insulators, a new topological phase emerges due to the effect of spin-orbit interaction even in the absence of an external magnetic field. Topological insulators can generate pure spin currents with high efficiency due to strong spin-orbit interaction and inversion symmetry breaking at edges.

Topological insulators are, for example, SnTe, Bi _1.5 Sb _0.5 Te _1.7 Se _1.3 , TlBiSe ₂ , Bi ₂ Te ₃ , Bi _1-x Sb _x , (Bi _1-x Sb _x ) ₂ such as _Te3 . These topological insulators can generate spin currents with high efficiency.

(antiferromagnetic coupling layer)
The antiferromagnetic coupling layer 4 is Ru or Ir, for example. When the thickness of the antiferromagnetic coupling layer 4 is set, antiferromagnetic coupling is imparted between the ferromagnetic layers (the first ferromagnetic layer 2 and the second ferromagnetic layer 3) in contact with the antiferromagnetic coupling layer, The directions of the magnetization vectors 2A and 3A are opposite to each other.

4A and 4B show antiferromagnetic coupling in the magnetic recording layer 11. FIG. In the magnetic recording layer 11, the magnetization vector 2A of the first ferromagnetic layer 2 and the magnetization vector 3A of the second ferromagnetic layer 3 are antiferromagnetically coupled, and are directed in opposite directions. In FIG. 4A, the magnetization vector 2A of the first ferromagnetic layer 2 is larger than the magnetization vector 3A of the second ferromagnetic layer 3, and as a result, the magnetization vector 11A of the magnetic recording layer 11 is the magnetization vector 2A of the first ferromagnetic layer. in the same direction. On the other hand, in FIG. 4B, the magnetization vector 3A of the second ferromagnetic layer 3 is larger than the magnetization vector 2A of the first ferromagnetic layer 2, and the magnetization vector 11A of the magnetic recording layer 11 is the magnetization vector 3A of the second ferromagnetic layer. in the same direction.

(non-magnetic layer)
A known material can be used for the non-magnetic layer 5 . For example, when the nonmagnetic layer 5 is made of an insulator (that is, when it is a tunnel barrier layer), Al ₂ O ₃ , SiO ₂ , Mg, MgAl ₂ O ₄ or the like can be used as the material. . In addition to these materials, the non-magnetic layer 5 can be made of a material in which a portion of Al, Si, or Mg is replaced with Zn, Be, or the like. Among these materials, MgO and MgAl ₂ O ₄ are materials capable of realizing coherent tunneling, and thus spins can be efficiently injected. Furthermore, MgAl ₂ O ₄ having a spinel crystal structure is superior to MgO in durability when a current is applied to the tunnel barrier layer, and the product can be guaranteed for a long period of time. When the nonmagnetic layer 5 is made of metal, Cu, Au, Ag, or the like can be used as the material.

(cap layer)
It is preferable to use a highly conductive material for the cap layer 9 . For example, Ru, Ta, Cu, Ag, Au, etc. can be used. The crystal structure of the cap layer 9 is appropriately selected from a face-centered cubic (fcc) structure, a hexagonal close-packed (hcp) structure, or a body-centered cubic (bcc) structure in accordance with the crystal structure of the adjacent ferromagnetic metal layer. is preferred.

(Element shape)
As shown in FIG. 1, in the spin current magnetization rotation type magnetoresistance effect element 100, the first surface 2a of the first ferromagnetic layer 2 in contact with the spin orbit torque wiring layer 1 is the nonmagnetic layer of the second ferromagnetic layer 3. It is preferably larger than the area of the second surface 2b in contact with 5. Since the volume of the magnetic recording layer 11 can also be increased by increasing the area of the first ferromagnetic layer 2, the data retention force can be increased.

(First ferromagnetic layer and second ferromagnetic layer)
The first ferromagnetic layer 2 is preferably a ferromagnetic material containing rare earth elements, and the second ferromagnetic layer 3 is preferably a ferromagnetic material containing Fe. A ferromagnetic material containing a rare earth element has strong crystal magnetic anisotropy and can stably retain data even if the size of the spin current rotating magnetization magnetoresistance effect element 100 is reduced. Also, when the first ferromagnetic layer 2 contains a rare earth element, the spin-orbit interaction in the first ferromagnetic layer 2 increases, and the spin diffusion length of the first ferromagnetic layer 2 decreases. Since the second ferromagnetic layer 3 is made of a ferromagnetic material containing Fe, coherent tunneling can be realized when the nonmagnetic layer 5 is MgO or MgAl ₂ O ₄ . As a result, the magnetoresistance ratio of the spin current rotation magnetization magnetoresistance effect element 100 is increased.

(spin resistance, spin resistivity)
The spin resistance is a quantity that quantitatively indicates how easy it is for a spin current to flow (difficulty in spin relaxation). Non-Patent Document 2 discloses a theoretical treatment of spin resistance. Reflection (return) of the spin current occurs at the interface of substances with different spin resistances. That is, only part of the spin current is injected from the material with low spin resistance to the material with high spin resistance.

ここで、λは材料のスピン拡散長、ρは材料の電気抵抗率、Ａは材料の断面積である。
非磁性体では、断面積Ａが等しい場合、式（１）のうち、スピン抵抗率であるρλの値によってスピン抵抗の大きさが決まる。 The spin resistance Rs is defined by the following formula (see Non-Patent Document 2).

where λ is the spin diffusion length of the material, ρ is the electrical resistivity of the material, and A is the cross-sectional area of the material.
In a non-magnetic material, if the cross-sectional areas A are the same, the magnitude of the spin resistance is determined by the value of ρλ, which is the spin resistivity, in Equation (1).

In the first embodiment, when the first ferromagnetic layer 2 is a ferromagnetic material containing rare earth elements and the second ferromagnetic layer 3 is a ferromagnetic material containing Fe, the first ferromagnetic layer 2 is a spin-orbit torque wiring. It absorbs the spin current generated from layer 1. Part of the spin current reaches the second ferromagnetic layer 3 unless the first ferromagnetic layer 2 absorbs the spin current and causes the spin-orbit torque due to the spin current to sufficiently act on the magnetization reversal of the first ferromagnetic layer 2 . . When the spin current reaches the second ferromagnetic layer 3, the spin current tries to orient the magnetization of the second ferromagnetic layer 3 in the same direction as the direction to orient the magnetization of the first ferromagnetic layer 2. do. At this time, since the magnetization directions of the first ferromagnetic layer 2 and the second ferromagnetic layer 3 are opposite to each other, the magnetization reversal of the second ferromagnetic layer 3 inhibits the magnetization reversal of the first ferromagnetic layer 2 . Therefore, it is preferable that the first ferromagnetic layer 2 has a low spin resistance and can easily absorb the spin current generated in the spin-orbit torque interconnection layer 1 . Also, the second ferromagnetic layer 3 is in contact with the non-magnetic layer 5 and realizes coherent tunneling, whereby a high magnetoresistance ratio can be obtained. An Fe-based ferromagnetic material is preferable for causing coherent tunneling, and when the second ferromagnetic layer 3 is a ferromagnetic material containing Fe, the spin current rotation magnetization magnetoresistance effect element 100 exhibits a high magnetoresistance ratio. show.

The first ferromagnetic layer 2 preferably contains CoFe alloy, FePt alloy, CoPd alloy, FePd alloy, CoCrPt alloy, HoFe alloy, or SmFe alloy. In particular, SmFe ₁₂ and HoFe ₂ are preferred. These materials are tetragonal crystals with the c-axis as the major axis, and have strong magnetocrystalline anisotropy in the c-axis direction. Due to the strong magnetocrystalline anisotropy, data can be stably retained even when the size of the spin current rotating magnetization magnetoresistance effect element 100 is small.

The thickness of the first ferromagnetic layer 2 is preferably thinner than the thickness of the second ferromagnetic layer 3 . When the first ferromagnetic layer 2 contains rare earth elements, the saturation magnetization of the first ferromagnetic layer 2 increases. When the second ferromagnetic layer 3 does not contain a rare earth element, the first ferromagnetic layer 2 is thinner than the second ferromagnetic layer 3 and can generate a magnetic field equivalent to that of the second ferromagnetic layer 3 . That is, even when the thickness of the first ferromagnetic layer 2 is thinner than the thickness of the second ferromagnetic layer 3, the magnetic field generated by the first ferromagnetic layer 2 and the magnetic field generated by the second ferromagnetic layer 3 can be canceled with each other. is possible. Further, when the second ferromagnetic layer 3 is thickened, the magnetoresistive ratio of the spin current rotation magnetization magnetoresistance effect element 100 can be increased at the time of reading. This is because, by thickening the second ferromagnetic layer 3, the spin-polarized current from the magnetization reference layer 6 can be sufficiently relaxed in the second ferromagnetic layer 3, and can contribute to an increase in resistance as magnetic scattering.

(Evaluation method)
The spin current magnetization rotation type magnetoresistive effect element 100 evaluates the difference in relative angle between the magnetization vectors 3A and 6A of the second ferromagnetic layer 3 and the magnetization reference layer 6 as a resistance value. For example, a current source is connected to both ends of the XY plane of the spin-orbit torque wiring layer 1 and energized. When the current value of the current source is sufficient, the magnetization of the first ferromagnetic layer 2 is reversed by the spin current generated in the spin-orbit torque interconnection layer 1 . Since the magnetization vector 3A of the second ferromagnetic layer 3 is magnetically coupled to the first ferromagnetic layer 2 and the antiferromagnetic coupling layer 4, the magnetization vector 3A of the first ferromagnetic layer 2 is reversed in the opposite direction. A current source and a voltmeter are installed at both ends of the spin-orbit torque wiring layer 1 and the magnetization reference layer 6, and a constant current or constant voltage is applied to the spin current rotating magnetization magnetoresistance effect element 100 to evaluate the resistance. Then, the relative angle between the magnetization vectors 3A and 6A of the second ferromagnetic layer 3 and the magnetization reference layer 6 can be evaluated. Moreover, by measuring while sweeping the magnetic field from the outside, the resistance change of the spin current rotating magnetization magnetoresistive effect element 100 can be observed. The relative angle of magnetization between the second ferromagnetic layer 3 and the magnetization reference layer 6 can be evaluated from the maximum and minimum resistance values.

The MR ratio is generally represented by the following formula.
MR ratio (%) = (R _AP −R _P )/R _P ×100
_RP is the resistance when the magnetization directions of the second ferromagnetic layer 3 and the magnetization reference layer 6 are parallel, and _RAP is the resistance when the magnetization directions of the second ferromagnetic layer 3 and the magnetization reference layer 6 are antiparallel. resistance.

(Second embodiment)
A spin current rotating magnetization magnetoresistive element 200 according to the second embodiment is similar to that of the first embodiment. Configurations common to those of the first embodiment are denoted by the same reference numerals, and descriptions thereof are omitted. The spin current rotation magnetization magnetoresistive element 200 differs from the spin current rotation magnetization magnetoresistive element 100 according to the first embodiment in the configuration of the magnetization reference layer 12 . The magnetization reference layer 12 has a first magnetization reference layer 16 , a second antiferromagnetic coupling layer 17 , and a second magnetization reference layer 18 in order from the spin-orbit torque wiring layer 1 . The first magnetization reference layer 16 and the second magnetization reference layer 18 are antiferromagnetically coupled by the second antiferromagnetic coupling layer 17 . As shown in FIG. 2, the directions of the magnetizations 16A and 18A of the first magnetization reference layer 16 and the second magnetization reference layer 18 are opposite to each other. With this structure, like the magnetic recording layer 11, the net magnetization of the entire magnetization reference layer 12 can be brought close to zero, and the magnetic flux generated from the magnetization reference layer 12 can be converted into another spin current magnetization rotation type magnetoresistive effect. The influence on the device can be reduced. Also, the cap layer 9 exhibits effects such as adjustment of the crystal orientation of the second magnetization reference layer 18 and induction of interfacial magnetic anisotropy by mixing electron orbits with the second magnetization reference layer 18 .

(Third embodiment)
FIG. 3 is a diagram showing a spin current rotation magnetization magnetoresistance effect element 300 according to the third embodiment. The spin current magnetization rotation type magnetoresistive effect element 300 has a magnetization reference layer 12 with a synthetic structure with a second antiferromagnetic coupling layer 17 . In the spin current rotation magnetization magnetoresistive effect element 300, the spin-orbit torque wiring layer 1 and the first ferromagnetic layer 2 extend in the XY plane.

When forming the spin current magnetization rotation type magnetoresistive effect element 300, it is preferable to continuously form films from the spin orbit torque wiring layer 1 to the cap layer 9 in order in a vacuum. This is because the interfacial state of each layer is active and the bonding of each layer is strong. Continuous film formation suppresses magnetic scattering at the interface, enhances magnetic coupling between adjacent layers, and makes efficient spin conduction between adjacent layers.

A spin current magnetization rotation type magnetoresistive effect element 300 is formed by processing a multilayer film into a predetermined element shape. The processing is performed by scraping the multilayer film, for example, by milling. For example, methods such as reactive ion etching (RIE) are frequently used in semiconductor processes, but ion beam etching (IBE) is preferable in consideration of magnetic damage to multilayer films. Since the multilayer film is removed by bombarding the multilayer film with accelerated ions in the IBE, the selectivity of the elements constituting the layers is low unlike the RIE. Therefore, when milling by IBE, the milling position of the multilayer film can be estimated by reading the intensity and time of the IBE beam and the secondary ion mass spectrometry (SIMS) signal generated when the multilayer film is milled. The spin-orbit torque wiring layer 1 of the spin current magnetization rotation type magnetoresistive effect element 300 is sufficiently thin and has a thickness of about 3 to 5 nm. This is because the spin diffusion length of the spin-orbit torque wiring layer 1 is about several nanometers, and setting a film thickness greater than this does not contribute to magnetization reversal. Also, increasing the film thickness increases the cross-sectional area of the spin-orbit torque wiring layer 1 . The magnetization of the first ferromagnetic layer 2 is reversed when the current density of the current flowing through the spin-orbit torque interconnection layer 1 exceeds a predetermined value (reversal current density). As the cross-sectional area of the spin-orbit torque wiring layer 1 increases, the spin-orbit torque wiring layer 1 requires more current, resulting in increased power consumption. For the above reasons, it is necessary to process the multilayer film by IBE and stop the process at an arbitrary height position of the spin-orbit torque wiring layer 1 . At this time, it is preferable to use the SIMS signal generated when the antiferromagnetic coupling layer 4 is shaved as a reference for the signal for stopping the processing by IBE. Ru and Ir are used for the antiferromagnetic coupling layer 4, which are heavy metals and can obtain a large SIMS signal. By using this signal as a reference, the processing of the element is stabilized and the reliability is improved. In addition, the expansion of the first ferromagnetic layer 2 in the XY plane makes it possible to increase the volume of the first ferromagnetic layer 2, thereby increasing the data holding power.

(Fourth embodiment)
FIG. 6 is a diagram showing a spin current rotating magnetization magnetoresistance effect element 400 according to the fourth embodiment. The spin current rotation magnetization magnetoresistance effect element 400 differs from the first embodiment in that the spin orbit torque wiring layer 1 is located in the +z direction from the magnetic recording layer 11, the nonmagnetic layer 5, the magnetization reference layer 6, and the cap layer 9. This is different from the spin current rotation magnetization type magnetoresistance effect element 100 . The same components as those of the spin current rotation magnetization magnetoresistive effect element 100 are denoted by the same reference numerals, and descriptions thereof are omitted.

In the spin current rotation magnetization magnetoresistance effect element 400 , the spin orbit torque wiring layer 1 is positioned in the +z direction from the magnetic recording layer 11 , nonmagnetic layer 5 , magnetization reference layer 6 and cap layer 9 . That is, the spin-orbit torque wiring layer 1 is located farther from the magnetic recording layer 11 , the non-magnetic layer 5 , the magnetization reference layer 6 and the cap layer 9 from the substrate Sub, which will be described later. The magnetization reference layer 6 is positioned closer to the substrate Sub described later than the magnetic recording layer 11 . The spin current magnetization rotation type magnetoresistance effect element 400 has a bottom pin structure.

The spin-orbit torque wiring layer 1 is stacked on the first ferromagnetic layer 2 and the insulating layer 90 in the +z direction. The insulating layer 90 is an insulating layer that insulates between wirings of multilayer wiring and between elements. The insulating layers 90 and 91 are made of, for example, silicon oxide (SiO _x ), silicon nitride (SiN _x ), silicon carbide (SiC), chromium nitride, silicon carbonitride (SiCN), silicon oxynitride (SiON), aluminum oxide (Al ₂ O ₃ ), zirconium oxide (ZrO _x ), and the like.

The first surface 1a and the second surface 1b of the spin-orbit torque wiring layer 1 have different height positions in the z-direction depending on the location. The first surface 1a is the surface of the spin-orbit torque interconnection layer 1 closer to the first ferromagnetic layer 2, and the second surface 1b is the surface opposite to the first surface 1a. Hereinafter, the portion of the first surface 1a that overlaps the first ferromagnetic layer 2 in the z-direction is referred to as the first surface 1aA, and the portion that does not overlap is referred to as the first surface 1aB. Hereinafter, the portion of the second surface 1b that overlaps the first ferromagnetic layer 2 in the z-direction is referred to as a second surface 1bA, and the portion that does not overlap is referred to as a second surface 1bB. The first surface 1aB is positioned in the +z direction from the first surface 1aA. The first surface 1aA is recessed in the -z direction with respect to the first surface 1aB due to a difference in polishing speed when the first surface 1a is subjected to chemical mechanical polishing (CMP), for example. The second surface 1bB is located in the +z direction from the second surface 1bA. The second surface 1b reflects the shape of the first surface 1a.

The spin current rotation magnetization magnetoresistive element 400 configured as described above can obtain the same effect as the spin current rotation magnetization magnetoresistive element 100 according to the first embodiment even if it has a bottom-pin structure. .

(Fifth embodiment)
A magnetic memory 1000 can be formed by arranging and operating a plurality of spin current rotation magnetization magnetoresistance effect elements 100 .

(Arrangement example 1)
In the magnetic memory 1000, the spin current rotating magnetization magnetoresistance effect elements 900 are generally arranged in a square lattice. FIG. 6 shows a structure in which spin current rotation magnetization type magnetoresistive effect elements 900 are arranged in a square lattice. A spin current rotation magnetization type magnetoresistance effect element 900 in FIG. 6 is the same as the spin current rotation magnetization type magnetoresistance effect element 100 according to the first embodiment. A magnetization vector 11A shown in FIG. 6 is the magnetization vector of the entire magnetic recording layer 11, and is the difference between the magnetization vector 2A of the first ferromagnetic layer 2 and the magnetization vector 3A of the second ferromagnetic layer 3 (FIGS. 4A, See Figure 4B). A write transistor and a select transistor are required in the spin current rotation magnetization type magnetoresistance effect element 900 .

FIG. 7 is a diagram showing a peripheral structure (including a write transistor and a select transistor) of a spin current rotation magnetization magnetoresistance effect element 900. As shown in FIG. The transistor Tr (write transistor and select transistor) has a gate electrode G, a gate insulating film GI, and a source region S and a drain region D formed in the substrate Sub. The substrate Sub is, for example, a semiconductor substrate.

Each of the transistors Tr, the spin current rotating magnetization magnetoresistive element 900, the word line WL, and the bit line BL are electrically connected via the conductive portion Cw. The conductive part Cw may be called, for example, a connection wiring or a via wiring. The conductive portion Cw includes a material having conductivity. The conductive portion Cw extends in the z direction.

An electrode 80 is formed in the spin current rotation magnetization type magnetoresistive element 900 . Electrode 80 includes a material having electrical conductivity. The electrodes 80 are connected to lead lines. A switching element (for example, a transistor) may be provided between the lead line RL and the electrode 80 . A switching element between the lead line RL and the electrode 80 is positioned, for example, in the depth direction (-y direction) of the paper surface of FIG.

Since it is necessary to pass a current on the XY plane of the spin-orbit torque wiring layer 1, the spin-current rotating magnetization magnetoresistive element 900 has a structure in which one axis is the major axis on the XY plane. In the magnetic memory 1000 shown in FIG. 6, the direction in which the plurality of elements are arranged is the same as the direction in which the magnetization vectors 11A of the respective magnetic recording layers 11 are oriented. In this case, the magnetic flux penetrates through the inside of each of the spin current rotating magnetization magnetoresistive elements 900 belonging to the same column, and wraps around so as to connect the spin current rotating magnetoresistive magnetoresistive elements 900 belonging to the same column at both ends. In this arrangement, the magnetic flux generated from the spin current rotation magnetization type magnetoresistive element 900 affects each other's spin current rotation magnetization type magnetoresistive elements. By suppressing the generation of the magnetic flux from the magnetic recording layer 11, the generation of the magnetic flux can be suppressed, and the influence of the magnetic flux between the respective elements can be suppressed.

(Arrangement example 2)
FIG. 8 shows a magnetic memory 2000 in which the method of arranging the spin current rotating magnetization magnetoresistive effect elements 100 is devised as a method of suppressing the arrangement problem of the arrangement example 1. FIG. In FIG. 8, the spin current magnetization rotation type magnetoresistive effect elements 100 are arranged in a patchwork pattern. That is, the positions in the x direction of the spin current rotation magnetization magnetoresistive effect element 100 belonging to the first row aligned in the x direction and the spin current magnetization rotation magnetoresistive effect element 100 belonging to the adjacent second row are are deviated from each other. In Arrangement Example 2, the distance between the closest spin current rotating magnetization magnetoresistive elements 100 is wider than in Arrangement Example 1. FIG. With this arrangement, it is possible to suppress the influence of the magnetic flux on the spin current rotation magnetization type magnetoresistance effect element 100 . FIG. 8 shows a patchwork arrangement of spin current rotating magnetization magnetoresistive elements 100 in Type-X. Type-X is a configuration in which the magnetization vector 11A of the entire magnetic recording layer 11 is oriented in the X direction and the spin orbit torque wiring layer 1 extends in the X direction. The easy axis direction of magnetization of the magnetic recording layer 11 of each spin current rotation magnetization type magnetoresistive element is the X direction. The direction connecting the closest spin current rotation magnetization magnetoresistive elements 100 is a direction that is tilted from the X direction by 45° toward the Y direction.

(Arrangement example 3)
FIG. 9 shows a patchwork arrangement of spin current magnetization rotating magnetoresistance effect elements 100 in Type-Y. With this arrangement, it is possible to suppress the influence of the magnetic flux on the spin current rotation magnetization type magnetoresistance effect element 100 . Type-Y is a configuration in which the magnetization vector 11A of the entire magnetic recording layer 11 is oriented in the Y direction, and the spin orbit torque wiring layer 1 extends in the X direction. The easy axis direction of magnetization of the magnetic recording layer 11 of each spin current magnetization rotation type magnetoresistive element is the Y direction. The direction connecting the closest spin current rotation magnetization magnetoresistance effect elements 100 is a direction inclined from the X direction to the Y direction by 45°.

DESCRIPTION OF SYMBOLS 100, 200, 300, 900... Spin current magnetization rotation type magnetoresistive effect element 1... Spin orbit torque wiring layer 2... First ferromagnetic layer 2A... Magnetization vector of first ferromagnetic layer 3... Second strong Magnetic layer 3A... Magnetization vector of second ferromagnetic layer 4... Antiferromagnetic coupling layer 5... Nonmagnetic layer 6... Magnetization reference layer 16... First magnetization reference layer 17... Second antiferromagnetic coupling Layer 18 Second magnetization reference layer 9 Cap layer 11 Magnetic recording layer 11A Magnetization vector of magnetic recording layer 12 Magnetization reference layer 13 Magnetic flux of magnetic recording layer

Claims (8)

a spin-orbit torque wiring layer;
a first ferromagnetic layer;
an antiferromagnetic coupling layer;
a second ferromagnetic layer;
a non-magnetic layer;
and a magnetization reference layer in this order,
The product of the saturation magnetization of the first ferromagnetic layer and the thickness of the first ferromagnetic layer is larger than the product of the saturation magnetization of the second ferromagnetic layer and the thickness of the second ferromagnetic layer. is also large,
The first ferromagnetic layer is a spin current rotating magnetization magnetoresistive element having a spin resistance lower than that of the second ferromagnetic layer . 2. The method according to claim 1 , wherein a first surface of said first ferromagnetic layer located on the spin orbit torque wiring layer side has a larger area than a second surface of said second ferromagnetic layer located on the nonmagnetic layer side. spin current magnetization rotation type magnetoresistive effect element. 3. The spin current magnetization rotating magnet according to claim 1, wherein said first ferromagnetic layer contains an alloy containing at least one element selected from Co, Fe and Ni and at least one rare earth element. resistance effect element. 4. The spin current magnetization rotation magnetoresistive element according to claim 3 , wherein said first ferromagnetic layer contains CoPt alloy, FePt alloy, CoPd alloy, FePd alloy, CoCrPt alloy, HoFe alloy, or SmFe alloy. 5. The spin current rotation magnetization magnetoresistive element according to claim 1 , wherein the thickness of said first ferromagnetic layer is thinner than the thickness of said second ferromagnetic layer. 6. The spin current rotation magnetization magnetoresistive element according to claim 1 , wherein said non-magnetic layer has a spinel crystal structure. A magnetic memory comprising a plurality of spin current rotation magnetization magnetoresistive elements according to any one of claims 1 to 6 . Having a plurality of spin current rotation magnetization magnetoresistive elements according to any one of claims 1 to 6 ,
the easy axis directions of magnetization of the first ferromagnetic layer and the second ferromagnetic layer constituting the first spin current rotation magnetization magnetoresistance effect element are the first direction;
A magnetic memory, wherein a direction connecting the first spin current rotation magnetization magnetoresistive element and the nearest second spin current rotation magnetization magnetoresistive element is different from the first direction.

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