JP2019176099A - Domain wall motion type magnetic recording element, domain wall motion type magnetoresistance effect element and magnetic memory - Google Patents

Abstract

To provide a domain wall motion type magnetic recording element capable of stably controlling a magnetization region ratio.SOLUTION: A domain wall motion type magnetic recording element 100 includes: a magnetic recording layer 1 having a granular structure constituted of a ferromagnetic crystal grain and a grain boundary phase; a first ferromagnetic layer 2 magnetically coupled to the magnetic recording layer 1; and two electrodes (a first electrode 3, a second electrode 4) which is arranged, spacing to sandwich the first ferromagnetic layer 2 in plan view, on the magnetic recording layer 1 and applies an electric current to the magnetic recording layer 1.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a domain wall motion type magnetic recording element, a domain wall motion type magnetoresistive effect element, and a magnetic memory.

  Attention has been focused on resistance change type magnetic recording devices that store data using resistance change type elements as next-generation nonvolatile memories that replace flash memories and the like that have seen limitations in miniaturization. Examples of the magnetic recording apparatus include an MRAM (Magnetorescent Random Access Memory), a ReRAM (Resistance Random Access Memory), and a PCRAM (Phase Change Random Access Memory).

  As a method of increasing the density (capacity) of the memory, there is a method of multi-value recording bits per element constituting the memory, in addition to a method of reducing the element itself constituting the memory.

  Patent Document 1 describes a domain wall motion type magnetic recording element capable of recording multivalued data by moving a domain wall in a magnetic recording layer. Patent Document 1 describes that multilevel data recording is stabilized by providing a trap site in a magnetic recording layer.

  It is required to stably control the domain wall position with a pulse current applied to the magnetic recording layer (domain wall moving layer) and to accurately read the change in the magnetization state due to the domain wall position change from the TMR resistance value.

International Publication No. 2009/101827

However, as schematically shown in FIG. 6, when the variation in the magnetic crystal grain size of the domain wall moving layer is large, the stability of the domain wall position and domain wall width varies, and the stable reading of the TMR resistance value is hindered. Here, FIG. 6A is a diagram schematically showing magnetic crystal grains and domain walls in the domain wall moving layer, and FIG. 6B is a schematic diagram showing the relationship between the position of the domain wall and the resistance value of the domain wall motion type magnetic recording element. It is a graph shown in. In FIG. 6A, the symbol DW indicates a domain wall, and the symbol P1 indicates a magnetic crystal grain. Further, in FIG. 6B, the input load on the horizontal axis corresponds to the position of the domain wall, the solid line shows an ideal resistance change, and the dotted line shows the resistance change when the variation of the magnetic crystal grain size is large. It is shown.
For example, when the domain wall motion layer is made of a CoPt alloy, the size of the magnetic crystal grains is usually about 1 to 30 nm, and a standard of general size variation (maximum size-minimum size) can be said with respect to the size. For example, it is about 1 to 5 nm.

  The present invention has been made in view of the above problems, and an object thereof is to provide a domain wall motion type magnetic recording element, a domain wall motion type magnetoresistive effect element, and a magnetic memory capable of stably controlling the magnetization region ratio.

  The present invention provides the following means in order to solve the above problems.

(1) A domain wall motion type magnetic recording element according to a first aspect of the present invention includes a magnetic recording layer having a granular structure composed of ferromagnetic crystal grains and a grain boundary phase, and magnetically coupled to the magnetic recording layer. A first ferromagnetic layer; and two electrodes disposed on the magnetic recording layer so as to sandwich the first ferromagnetic layer in plan view and applying a current to the magnetic recording layer. I have.

(2) In the above aspect, a spin orbit torque wiring layer bonded to the magnetic recording layer may be provided.

(3) A domain wall motion type magnetic recording element according to the second aspect of the present invention is magnetically coupled to a magnetic recording layer having a granular structure composed of ferromagnetic crystal grains and a grain boundary phase, and the magnetic recording layer. A first ferromagnetic layer; and a magnetic field application wiring that is electrically insulated from the magnetic recording layer and extends in a direction intersecting the magnetic recording layer.

(4) In any one of the above aspects, the material of the ferromagnetic crystal grains of the magnetic recording layer is a single element of Co, Ni, or Fe, or an alloy containing at least one of Co, Ni, and Fe It may be.

(5) In any one of the above aspects, the material of the grain boundary phase of the magnetic recording layer may be a nonmagnetic material containing at least one of O, N, and F.

(6) In any one of the above embodiments, the molar ratio of the material α of the ferromagnetic crystal grains and the material β of the grain boundary phase constituting the magnetic recording layer is x: 100−x (10 <x <90) It may be.

(7) In any one of the above aspects, a magnetic coupling layer may be provided between the magnetic recording layer and the first ferromagnetic layer.

(8) A domain wall motion type magnetoresistive effect element according to a third aspect of the present invention includes the domain wall motion type magnetic recording element according to the first aspect and a nonmagnetic material disposed on the first ferromagnetic layer. And a second ferromagnetic layer disposed on the nonmagnetic layer.

(9) A magnetic memory according to the fourth aspect of the present invention includes a plurality of domain wall motion magnetoresistive elements according to the second aspect.

  According to the domain wall motion type magnetic recording element of the present invention, an object is to provide a domain wall motion type magnetic recording element capable of stably controlling the magnetization region ratio.

1 is a perspective view schematically showing a domain wall motion type magnetic recording element according to a first embodiment of the present invention. FIG. FIG. 3 is a diagram schematically showing ferromagnetic crystal grains and crystal grain distribution boundaries in a magnetic recording layer in a domain wall motion type magnetic recording element of the present invention. It is a graph which shows typically the relation between the position of a crystal grain distribution boundary, and the resistance value at the time of producing a domain wall motion type magnetoresistive effect element. It is the perspective view which showed typically the aspect provided with the magnetic coupling layer between the magnetic-recording layer and the 1st ferromagnetic layer. It is the perspective view which showed typically the domain wall motion type | mold magnetic recording element concerning 2nd Embodiment of this invention. It is the perspective view which showed typically the domain wall motion type | mold magnetoresistive effect element concerning one Embodiment of this invention. It is the figure which showed typically the magnetic crystal grain and domain wall in the domain wall moving layer of the conventional domain wall motion type | mold magnetoresistive effect element. It is a graph which shows typically the relation between the position of a domain wall, and the resistance value of a domain wall motion type magnetic recording element.

  Hereinafter, the present embodiment will be described in detail with appropriate reference to the drawings. In the drawings used in the following description, in order to make the characteristics of the present invention easier to understand, there are cases where the characteristic parts are enlarged for the sake of convenience, and the dimensional ratios of the respective components are different from actual ones. is there. The materials, dimensions, and the like exemplified in the following description are merely examples, and the present invention is not limited to these, and can be implemented with appropriate modifications within the scope of the effects of the present invention.

(Domain wall magnetic recording element)
“First Embodiment”
FIG. 1 is a perspective view schematically showing a domain wall motion type magnetic recording element 100 according to the first embodiment of the present invention.
The domain wall motion type magnetic recording element 100 includes a magnetic recording layer 1 having a granular structure composed of ferromagnetic crystal grains and a grain boundary phase, a first ferromagnetic layer 2 magnetically coupled to the magnetic recording layer 1, and a magnetic recording. Two electrodes (a first electrode 3 and a second electrode 4) disposed on the layer 1 so as to sandwich the first ferromagnetic layer 2 in a plan view and apply a current to the magnetic recording layer 1. It is equipped with.
The ferromagnetic crystal grains are preferably columnar, and in this specification, the columnar ferromagnetic crystal grains may be referred to as ferromagnetic crystal grain columns.

<Magnetic recording layer>
The magnetic recording layer 1 has a granular structure composed of ferromagnetic crystal grains and a grain boundary phase. As a material of the magnetic recording layer 1, a material used as a material of the magnetic recording layer in the magnetic recording medium may be used. The ferromagnetic crystal grains are preferably columnar.
As the granular structure, a grain boundary phase made of a nonmagnetic and insulating material can be used, or a nonmagnetic metal (for example, Cu, Ag, Au, etc., or one of them) It is also possible to use an alloy comprising one alloy. Hereinafter, the case where the grain boundary phase is a nonmagnetic and insulating material is referred to as a ferromagnetic metal-insulating granular material, and the case where the grain boundary phase is a nonmagnetic metal is referred to as a ferromagnetic metal-nonmagnetic metal granular material. is there.
In the case of a ferromagnetic metal-insulating granular material, for example, in a CoPt alloy (ferromagnetic metal) -SiO ₂ (oxide) -based granular material, fine ferromagnetic crystal grains of 10 μm or less can be formed. And a CoPt alloy and exhibit high perpendicular magnetic anisotropy.
When a ferromagnetic metal-nonmagnetic metal granular material is used, a function of rotating or reversing the magnetization by supplying a spin current to the first ferromagnetic layer 2 can be exhibited, similarly to a spin orbit torque wiring layer described later.
The ferromagnetic metal-nonmagnetic metal granular material is a nanometer-scale ferromagnetic metal fine particle dispersed in a nonmagnetic metal matrix, and mainly a combination of metals that are not solid-solved with each other, for example, Fe / Ag, Examples thereof include Fe / Cu, Co / Cu, Co / Au, and Fe / Au.

The granular structure can be formed by vacuum sputtering in the same manner as the method used for forming the magnetic recording layer of the magnetic recording medium. The size (or grain size) of the ferromagnetic crystal grains can be controlled by sputtering conditions. In addition, the size of the ferromagnetic crystal grains can be controlled by the thickness of the underlayer (for example, the Ru layer) used for forming the granular structure.
Therefore, compared with the domain wall motion layer of the conventional domain wall motion type magnetoresistive effect element, the size (or grain size) of the ferromagnetic crystal grains and the variation thereof can be suppressed, and writing and reading can be performed stably. Become.

Unlike the conventional continuous film of ferromagnetic material, the magnetic recording layer 1 has a structure in which ferromagnetic crystal grains responsible for magnetization are discretely arranged in the layer. Therefore, the magnetic recording layer 1 does not have a domain wall defined as a boundary between two magnetic domains having magnetizations opposite to each other, but a boundary between two regions each having a large number of ferromagnetic crystal grains having magnetizations opposite to each other ( Hereinafter, a configuration having a “crystal grain distribution boundary” may be employed. FIG. 2A is a schematic plan view schematically showing the vicinity of a crystal grain distribution boundary when viewed in plan from the z direction. In FIG. 2A, the symbol B indicates a crystal grain distribution boundary, and the symbol P0 indicates a magnetic crystal grain.
FIG. 2B schematically shows the relationship between the position of the boundary between two regions each having a large number of ferromagnetic crystal grains having opposite magnetizations and the resistance value when a domain wall motion type magnetoresistive effect element described later is fabricated. It is a graph to show. In FIG. 2B, the horizontal axis corresponds to the position of the crystal grain distribution boundary or the magnetization region ratio.

  The magnetic recording layer 1 extends in the x direction. The magnetic recording layer 1 has a crystal grain distribution boundary B inside. The crystal grain distribution boundary B is a boundary between two regions (first crystal grain distribution region 1A and second crystal grain distribution region 1B) each having a large number of ferromagnetic crystal grains having magnetizations in opposite directions. In the state of the domain wall motion type magnetic recording element 100 shown in FIG. 1, the first crystal grain distribution region 1A has many ferromagnetic crystal grains having magnetization (M1) oriented in the −z direction, and the second crystal grain distribution region. There are many ferromagnetic crystal grains having magnetization (M2) in which 1B is oriented in the + z direction.

The domain wall motion type magnetic recording element 100 records data in multiple values according to the position of the crystal grain distribution boundary B in the magnetic recording layer 1. When the crystal grain distribution boundary B moves, the ratio between the first crystal grain distribution region 1A and the second crystal grain distribution region 1B in the magnetic recording layer 1 changes.
The crystal grain distribution boundary B moves by passing a current in the extending direction of the magnetic recording layer 1 and / or applying an external magnetic field.
For example, when a current pulse of spin-polarized current is applied from the first electrode 3 to the second electrode 4, the second crystal grain distribution region 1B expands in the direction of the first crystal grain distribution region 1A, and the crystal grain distribution boundary B Moves in the direction of the first crystal grain distribution region 1A. On the other hand, when a current pulse of spin-polarized current is applied from the second electrode 4 to the first electrode 3, the first crystal grain distribution region 1A expands in the direction of the second crystal grain distribution region 1B, and the crystal grain distribution boundary B Moves in the direction of the second crystal grain distribution region 1B.
That is, the position of the crystal grain distribution boundary B can be controlled by setting the direction and intensity of the spin-polarized current that flows through the first electrode 3 and the second electrode 4.

  In order to move the grain distribution boundary B by applying an external magnetic field, a magnetic field application wiring that is electrically insulated from the magnetic recording layer 1 and extends in a direction intersecting the magnetic recording layer 1 is provided. It may be provided. A magnetic field is generated by Ampere's law by passing a current through the magnetic field application wiring. The direction of the generated magnetic field can be reversed depending on the direction of the current flowing through the magnetic field application wiring. Therefore, the magnetic field application wiring is disposed in the vicinity of both ends of the magnetic recording layer 1, and the crystal grain distribution boundary B of the magnetic recording layer 1 can be moved by a magnetic field created by passing a current through the magnetic field application wiring.

The ferromagnetic crystal grain material of the magnetic recording layer may be any one of Co, Ni, and Fe, or an alloy containing at least one of Co, Ni, and Fe.
For example, CoPt, CoCrPt, FePt, and the like are materials that are often used in making a granular structure. If these materials are used, the granular structure can be easily made.

The material of the grain boundary phase of the magnetic recording layer can be a nonmagnetic material containing at least one of O, N, and F. Specifically, ZrO ₂ , Cr ₂ O ₃ , Y ₂ O ₃ , Al ₂ O ₃ , MnO, TiO ₂ , WO ₂ , WO ₃ , SiO ₂ , Mn ₃ O ₄ , Co ₃ O ₄ , MoO ₃ , B ₂ O ₃ , TaN, TaO, MgO, MgF ₂ or the like can be used.

The volume ratio of the ferromagnetic crystal grain material α and the grain boundary phase material β constituting the magnetic recording layer is preferably x: 100−x (10 <x <90).
In the granular structure of the combination of the oxide grain boundary phase and CoPt alloy particles exemplified above, in the case of Co ₈₀ Pt ₂₀ -30 vol% oxide, the coercive force increases in descending order, B ₂ O ₃ , WO ₃ , MoO ₃ , TiO ₂ , SiO ₂ .

As shown in FIG. 3, a magnetic coupling layer 5 may be provided between the magnetic recording layer 1 and the first ferromagnetic layer 2.
The magnetic coupling layer 5 generates a large antiferromagnetic exchange coupling between the magnetic recording layer 1 and the first ferromagnetic layer 2, thereby magnetically connecting the magnetic recording layer 1 and the first ferromagnetic layer 2. Has the function of strengthening strong bonds.
As a material of the magnetic coupling layer 5, any one of Ru, Ir, and Rh or an alloy containing at least one of Ru, Ir, and Rh is preferable.

<First ferromagnetic layer>
The first ferromagnetic layer 2 is made of a ferromagnetic material. Examples of the ferromagnetic material constituting the first ferromagnetic layer 2 include a metal selected from the group consisting of Cr, Mn, Co, Fe, and Ni, an alloy containing one or more of these metals, and these metals and B An alloy containing at least one element selected from C, C, and N can be used. Specifically, Co-Fe, Co-Fe -B, Ni-Fe, include Coho 2, SmFe ₁₂ or the like.

The material constituting the first ferromagnetic layer 2 may be a Heusler alloy. Heusler alloys are half metal and have a high spin polarizability. A Heusler alloy is an intermetallic compound having a chemical composition of X ₂ YZ, X is a transition metal element or noble metal element of Co, Fe, Ni, or Cu group on the periodic table, and Y is Mn, V, Cr. Alternatively, it is a Ti group transition metal or X element species, and Z is a typical element from Group III to Group V. For example, as a Heusler _{alloy, Co 2 FeSi, Co 2 FeGe} , Co 2 FeGa, Co 2 MnSi, Co 2 Mn 1-a Fe a Al b Si 1-b, Co 2 FeGe 1-c Ga c , and the like.

  The first ferromagnetic layer 2 may be an in-plane magnetization film having an easy axis in the xy plane or a perpendicular magnetization film having an easy axis in the z direction. In FIG. 1, the first ferromagnetic layer 2 is an in-plane magnetization film.

  The film thickness of the first ferromagnetic layer 2 is preferably 2.5 nm or less, preferably 2.0 nm or less, when the easy axis of magnetization of the first ferromagnetic layer 2 is the z direction (vertical magnetization film). More preferably. In order to secure a sufficient amount of magnetization, the film thickness of the first ferromagnetic layer 2 is preferably 1.0 nm or more. When the film thickness of the first ferromagnetic layer 2 is reduced, perpendicular magnetic anisotropy (interface perpendicular magnetic anisotropy) is added to the first ferromagnetic layer 2 at the interface between the first ferromagnetic layer 2 and another layer. it can.

  The first ferromagnetic layer 2 is magnetically coupled to the magnetic recording layer 1. Therefore, the first ferromagnetic layer 2 reflects the magnetic state of the magnetic recording layer 1. When the first ferromagnetic layer 2 and the magnetic recording layer 1 are ferromagnetically coupled, the magnetic state of the first ferromagnetic layer 2 is the same as the magnetic state of the magnetic recording layer 1, and the first ferromagnetic layer 2 and the magnetic recording layer 1 are magnetic. When the recording layer 1 is antiferromagnetically coupled, the magnetic state of the first ferromagnetic layer 2 is opposite to the magnetic state of the magnetic recording layer 1.

<First electrode, second electrode>
The first electrode 3 and the second electrode 4 are disposed at a position sandwiching the first ferromagnetic layer 2 in the x direction when viewed in plan from the z direction.

The domain wall motion type magnetic recording element 100 according to the present embodiment can be manufactured using a known film forming means. The same applies to a domain wall motion type magnetic recording element according to an embodiment described later.
For example, a granular magnetic recording layer can also be formed by using a known granular structure forming method. When forming a granular structure, for example, a granular structure is often formed thereon using a Ru underlayer. By controlling the thickness of the underlayer, the diameter of the granular crystal column can be controlled. If this underlayer hinders the effects of the present invention, the order of layer formation may be devised, and the underlayer may be removed by polishing after forming the granular structure. When removing the underlying layer, a part of the granular structure on the growth end side or the growth source side may be removed to make the diameter of each columnar shape of the granular structure more uniform.
The ferromagnetic crystal column can be single-domained with a material having a weak magnetic anisotropy such as permalloy and having a diameter of 40 nm or less, and can be single-domaind with a material having a strong magnetic anisotropy such as CoPt even with a diameter of about 300 nm. . In the case of a ferromagnetic crystal grain column having a diameter as large as several hundred nm or more, it is necessary to consider the dynamics that only one end of one ferromagnetic crystal grain column undergoes magnetization reversal and then the domain wall moves. . Therefore, from the viewpoint of the size that causes magnetization reversal almost simultaneously in the ferromagnetic crystal grain column, the diameter is 100 nm or less, more preferably 80 nm or less, and further preferably 60 nm or less.

“Second Embodiment”
FIG. 4 is a perspective view schematically showing a domain wall motion type magnetic recording element 200 according to the second embodiment of the present invention. In the domain wall motion type magnetic recording element 100 shown in FIGS. 1 and 3, the same members are denoted by the same reference numerals and description thereof is omitted. The contents described in the first embodiment are also applied to this embodiment.
The domain wall motion type magnetic recording element 200 has a configuration in which a spin orbit torque wiring layer 11 joined to the magnetic recording layer 1 is further provided in addition to the configuration of the domain wall motion type magnetic recording element 100 according to the first embodiment.
In the configuration shown in FIG. 4, the spin orbit torque wiring layer 11 is disposed on the surface of the magnetic recording layer 1 opposite to the first ferromagnetic layer 2, but is not limited thereto.

In the domain wall motion type magnetic recording element according to the present embodiment, the current supplied from one of the first electrode 3 and the second electrode 4 flows through the magnetic recording layer 1 and the spin orbit torque wiring layer 11.
A feature is that when a current flows through the spin orbit torque wiring layer, a spin current is generated, and this spin current contributes to the magnetization reversal of the ferromagnetic crystal grains constituting the granular structure. That is, in the domain wall motion type magnetic recording element according to the present embodiment, the magnetization reversal by the current flowing in the magnetic recording layer 1 is performed in the same manner as the magnetization reversal of the ferromagnetic crystal grains in the domain wall motion type magnetic recording element of the first embodiment. In addition, the magnetization reversal due to the spin current diffused from the spin orbit torque wiring layer contributes to the magnetization reversal.
When the magnetic recording layer is made of a ferromagnetic metal-insulator system granular material, it depends on the thickness of the insulating grain boundary phase, but usually the resistance of the magnetic recording layer is larger than the resistance of the spin orbit torque wiring layer. The contribution of magnetization reversal due to is increased.
In the domain wall motion type magnetic recording element according to the present embodiment, either the contribution of the magnetization reversal due to the spin current or the contribution of the magnetization reversal due to the spin polarization current may be large.

<Spin orbit torque wiring layer>
The spin orbit torque wiring layer 11 extends in the X direction. The spin orbit torque wiring layer 11 is connected to one surface of the magnetic recording layer 1 in the Z direction. The spin orbit torque wiring layer 11 may be directly connected to the magnetic recording layer 1 or may be connected via another layer.

  It is preferable that the layer interposed between the spin orbit torque wiring layer 11 and the magnetic recording layer 1 does not dissipate the spin propagating from the spin orbit torque wiring layer 11. For example, it is known that silver, copper, magnesium, aluminum, and the like have a long spin diffusion length of 100 nm or more and are difficult to dissipate spin.

Moreover, it is preferable that the thickness of this layer is below the spin diffusion length of the substance which comprises a layer.
If the thickness of the layer is less than or equal to the spin diffusion length, the spin propagating from the spin orbit torque wiring layer 11 can be sufficiently transmitted to the magnetic recording layer 1.

  The spin orbit torque wiring layer 11 is made of a material that generates a spin current by a spin Hall effect when a current flows. As such a material, any material that can generate a spin current in the spin orbit torque wiring layer 11 is sufficient. 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 generates a spin current and a portion composed of a material that does not generate a spin current.

  Based on the spin-orbit interaction when a current is passed through the material, the spin current is induced by bending the first spin S1 and the second spin S2 in the directions orthogonal to the direction of the current. Called the Hall effect. The normal Hall effect and the spin Hall effect are common in that the moving (moving) charge (electrons) can bend in the moving (moving) direction, but the normal Hall effect is that the charged particles moving in the magnetic field exert Lorentz force. In contrast to this, the direction of motion is bent, but the spin Hall effect is greatly different in that the direction of movement is bent only by the movement of electrons (only the current flows) even though there is no magnetic field.

  Since the number of electrons of the first spin S1 is equal to the number of electrons of the second spin S2 in a non-magnetic material (a material that is not a ferromagnetic material), the surface of the spin orbit torque wiring layer 11 on which the magnetic recording layer 1 is disposed. The number of electrons of the first spin S1 going in the direction is equal to the number of electrons of the second spin S2 going in the opposite direction to the electrons of the first spin S1. Therefore, the current as a net flow of charge is zero. This spin current without current is particularly called a pure spin current.

Here, when 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 _JS , _JS = J _↑ −J _↓ . In FIG. 1, _JS flows upward in the figure as a pure spin current. Here, J _S is an electron flow having a polarizability of 100%.

  The spin orbit torque wiring layer 11 may include a nonmagnetic heavy metal. Here, the heavy metal is used to mean a metal having a specific gravity equal to or higher than yttrium. The spin orbit torque wiring layer 11 may be made of only nonmagnetic heavy metal.

  In this case, the nonmagnetic heavy metal is preferably a nonmagnetic metal having an atomic number of 39 or more having d electrons or f electrons in the outermost shell. This is because such a nonmagnetic metal has a large spin-orbit interaction that causes a spin Hall effect. The spin orbit torque wiring layer 11 may be made of only a non-magnetic metal having an atomic number of 39 or more having d electrons or f electrons in the outermost shell.

Normally, when a current is passed through a metal, all electrons move in the opposite direction of the current regardless of the spin direction, whereas a non-magnetic metal having a large atomic number having d electrons or f electrons in the outermost shell. Since the spin-orbit interaction is large, the direction of electron movement depends on the direction of electron spin due to the spin Hall effect, and a pure spin current _JS is likely to occur.

  The spin orbit torque wiring layer 11 may contain a magnetic metal. The magnetic metal refers to a ferromagnetic metal or an antiferromagnetic metal. This is because if a non-magnetic metal contains a trace amount of magnetic metal, the spin-orbit interaction is enhanced and the spin current generation efficiency for the current flowing through the spin-orbit torque wiring layer 11 can be increased. The spin orbit torque wiring layer 11 may be made of only an antiferromagnetic metal.

  Since the spin-orbit interaction is caused by the intrinsic internal field of the material of the spin-orbit torque wiring material, a pure spin current is generated even in a nonmagnetic material. When a small amount of magnetic metal is added to the spin orbit torque wiring material, the spin current generation efficiency is improved because the electron spin that flows through the magnetic metal itself is scattered. However, if the amount of magnetic metal added is excessively increased, the generated spin current is scattered by the added magnetic metal, and as a result, the effect of reducing the spin current becomes stronger. Therefore, it is preferable that the molar ratio of the magnetic metal added is sufficiently smaller than the molar ratio of the main component of the spin generation part in the spin orbit torque wiring. As a guide, the molar ratio of the magnetic metal added is preferably 3% or less.

  The spin orbit torque wiring layer 11 may include a topological insulator. The spin orbit torque wiring layer 11 may be composed only of a topological insulator. A topological insulator is a substance in which the inside of the substance is an insulator or a high-resistance substance, but a spin-polarized metal state is generated on the surface thereof. Substances have something like an internal magnetic field called spin-orbit interaction. Therefore, even without an external magnetic field, a new topological phase appears due to the effect of spin-orbit interaction. This is a topological insulator, and a pure spin current can be generated with high efficiency by strong spin-orbit interaction and breaking inversion symmetry at the edge.

As the topological insulator, 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 Te ₃ are preferable. These topological insulators can generate a spin current with high efficiency.

<Principle of writing to magnetic recording layer>
The principle of writing to the magnetic recording layer of the domain wall motion type magnetic recording element of the second embodiment is different from that of the domain wall motion type magnetic recording element of the first embodiment.
In the domain wall motion type magnetic recording element of the first embodiment, the ratio of the first crystal grain distribution region and the second crystal grain distribution region is changed by passing a current through the magnetic recording layer in the in-plane direction (X direction). And wrote. That is, writing was performed by moving the position of the crystal grain distribution boundary in the magnetic recording layer in the X direction by flowing a current in the in-plane direction (X direction) through the magnetic recording layer. This writing mode is similar to the conventional domain wall motion type magnetic recording element, although there is a difference between the crystal grain distribution boundary and the domain wall.
On the other hand, in the domain wall motion type magnetic recording element of the second embodiment, a spin current is generated by passing a current I ₁ through the spin orbit torque wiring layer 11, and this spin current is injected into the magnetic recording layer. The writing is performed. That is, the spin current injected into the magnetic recording layer can reverse the magnetization of the ferromagnetic crystal grains constituting the granular structure of the magnetic recording layer by spin orbit torque (SOT). Thereby, the ferromagnetic crystal grains having magnetization oriented in the first direction (for example, + Z direction) in the magnetic recording layer and the second direction (for example, -Z direction) which is opposite to the first direction. The total volume ratio (volume ratio) with the ferromagnetic crystal grains having magnetization oriented in the direction changes. This volume ratio corresponds to the horizontal axis of FIG. 2B, and changing this volume ratio corresponds to writing. Further, by reversing the direction of the current flowing through the spin orbit torque wiring layer 11, the direction of magnetization of the ferromagnetic crystal grains to be reversed can be reversed.
In both the domain wall motion type magnetic recording element of the first embodiment and the domain wall motion type magnetic recording element of the second embodiment, the total volume ratio of ferromagnetic crystal grains oriented in the same direction (in this specification, “magnetization region ratio”) It is common to write by changing

(Domain wall moving magnetoresistive element)
FIG. 5 is a perspective view schematically showing a domain wall motion type magnetoresistive effect element 300 according to an embodiment of the present invention.
The domain wall motion type magnetoresistive element 300 includes a magnetic recording layer 1 having a granular structure composed of ferromagnetic crystal grains and a grain boundary phase, a first ferromagnetic layer 2 magnetically coupled to the magnetic recording layer 1, The nonmagnetic layer 13 bonded to the first ferromagnetic layer 2, the second ferromagnetic layer 14 bonded to the nonmagnetic layer 13, and the first ferromagnetic layer 2 sandwiched between the magnetic recording layer 1 in plan view. And two electrodes (first electrode 3 and second electrode 4) for applying a current to the magnetic recording layer 1 are provided.
The configuration 20 in which the first ferromagnetic layer 2, the nonmagnetic layer 13, and the second ferromagnetic layer 14 are combined is a configuration of a normal magnetoresistive effect element. Can be applied.

<Second ferromagnetic layer>
The domain wall motion type magnetoresistive element 300 functions by the magnetization of the second ferromagnetic layer 14 being fixed in one direction and the magnetization direction of the first ferromagnetic layer 2 relatively changing. When applied to a coercive force difference type (pseudo spin valve type) MRAM, the coercivity of the second ferromagnetic layer 14 is greater than the coercivity of the first ferromagnetic layer 2. When applied to an exchange bias type (spin valve type) MRAM, the magnetization direction of the second ferromagnetic layer 14 is fixed by exchange coupling with the antiferromagnetic layer.

  The domain wall motion magnetoresistive element 300 is a tunneling magnetoresistance (TMR) element when the nonmagnetic layer 13 is made of an insulator, and a giant magnetoresistance when the nonmagnetic layer 13 is made of metal. (GMR: Giant Magnetoresistance) element.

  As a layered configuration of the domain wall motion type magnetoresistive effect element 300, a known layered configuration of the domain wall motion type magnetoresistive effect element can be adopted. For example, each layer may be composed of a plurality of layers, or may be provided with other layers such as an antiferromagnetic layer for fixing the magnetization direction of the second ferromagnetic layer 14. The second ferromagnetic layer 14 corresponds to a fixed layer or a reference layer, and the first ferromagnetic layer 2 corresponds to a layer called a free layer or a storage layer.

  As the material of the second ferromagnetic layer 14, a known material can be used, and the same material as that of the first ferromagnetic layer 2 can be used. Since the first ferromagnetic layer 2 is a perpendicular magnetization film, the second ferromagnetic layer 14 is also preferably a perpendicular magnetization film.

  Further, when the second ferromagnetic layer 14 and the first ferromagnetic layer 2 are in-plane magnetization films, the second strong magnetic layer 14 has a second strong magnetic layer 14 in order to increase the coercive force of the second ferromagnetic layer 14 with respect to the first ferromagnetic layer 2. An antiferromagnetic material such as IrMn or PtMn may be used as a material in contact with the magnetic layer 14. Further, in order to prevent the leakage magnetic field of the second ferromagnetic layer 14 from affecting the first ferromagnetic layer 102, a synthetic ferromagnetic coupling structure may be used.

<Nonmagnetic layer>
A known material can be used for the nonmagnetic layer 13. For example, when the nonmagnetic layer 13 is made of an insulator (when it is a tunnel barrier layer), the material can be Al ₂ O ₃ , SiO ₂ , MgO, MgAl ₂ O ₄ , or the like. In addition to these, a material in which a part of Al, Si, Mg is substituted with Zn, Be, or the like can also be used. Among these, MgO and MgAl2O4 are materials that can realize a coherent tunnel, so that spin can be injected efficiently. When the nonmagnetic layer 13 is made of metal, Cu, Au, Ag, or the like can be used as the material. Furthermore, when the nonmagnetic layer 13 is made of a semiconductor, Si, Ge, CuInSe ₂ , CuGaSe ₂ , Cu (In, Ga) Se _2, or the like can be used as the material.

In a product-sum operation unit including a product operation unit having a plurality of product operation elements and a sum operation unit, the domain wall motion magnetoresistive effect element of the present invention can be used as the product operation element.
Further, in a neuromorphic device including an input layer, a hidden layer, an output layer, and a product-sum operation unit, the domain wall motion magnetoresistive effect element of the present invention is used as a product operation element constituting the product-sum operation unit. be able to.

(Magnetic memory)
A magnetic memory according to an embodiment of the present invention includes a plurality of domain wall motion magnetoresistive elements of the present invention.

DESCRIPTION OF SYMBOLS 1 Magnetic recording layer 2 1st ferromagnetic layer 3 1st electrode 4 2nd electrode 5 Magnetic coupling layer 11 Spin orbit torque wiring layer 13 Nonmagnetic layer 14 2nd ferromagnetic layer 100, 200 Domain wall motion type magnetic recording element 300 Domain wall motion Type magnetoresistive effect element

Claims (9)

A magnetic recording layer having a granular structure composed of ferromagnetic crystal grains and a grain boundary phase;
A first ferromagnetic layer magnetically coupled to the magnetic recording layer;
On the magnetic recording layer, there is provided a domain wall motion type magnetism provided with two electrodes spaced apart so as to sandwich the first ferromagnetic layer in a plan view and applying a current to the magnetic recording layer Recording element.   The domain wall motion type magnetic recording element according to claim 1, further comprising a spin orbit torque wiring layer bonded to the magnetic recording layer. A magnetic recording layer having a granular structure composed of ferromagnetic crystal grains and a grain boundary phase;
A first ferromagnetic layer magnetically coupled to the magnetic recording layer;
A magnetic domain wall displacement type magnetic recording element comprising: a magnetic field applying wiring that is electrically insulated from the magnetic recording layer and extends in a direction intersecting the magnetic recording layer.   The material of the ferromagnetic crystal grains of the magnetic recording layer is any one of Co, Ni, and Fe, or an alloy containing at least one of Co, Ni, and Fe. The domain wall motion type magnetic recording element according to claim 1.   5. The domain wall motion type magnetic recording element according to claim 1, wherein the material of the grain boundary phase of the magnetic recording layer is a nonmagnetic material containing at least one of O, N, and F. 6. .   6. The volume ratio of the material α of the ferromagnetic crystal grains and the material β of the grain boundary phase constituting the magnetic recording layer is x: 100−x (10 <x <90). The domain wall motion type magnetic recording element according to claim 1.   The domain wall motion type magnetic recording element according to claim 1, further comprising a magnetic coupling layer between the magnetic recording layer and the first ferromagnetic layer. A domain wall motion type magnetic recording element according to any one of claims 1 to 7,
A nonmagnetic layer disposed on the first ferromagnetic layer;
A domain wall motion type magnetoresistive effect element comprising: a second ferromagnetic layer disposed on the nonmagnetic layer.   A magnetic memory comprising a plurality of domain wall motion type magnetoresistive effect elements according to claim 8.

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