MAGNETIC ELEMENT AND MAGNETIC MEMORY

This magnetic element includes a spin orbit torque wiring, and a laminate including a first ferromagnetic layer. The spin orbit torque wiring includes three or more layers. Combinations of materials of the layers in the spin orbit torque wiring are asymmetric in a lamination direction. A sequence of material types in which the materials of the layers of the spin orbit torque wiring are arranged from a first surface in contact with the laminate toward a second surface on a side opposite to the first surface differs from a sequence of material types in which the materials of the layers of the spin orbit torque wiring are arranged from the second surface toward the first surface.

DESCRIPTION OF RELATED ART

Giant magnetoresistive (GMR) elements constituted of a multilayer film with a ferromagnetic layer and a non-magnetic layer, and tunnel magnetoresistive (TMR) elements using an insulating layer (a tunnel barrier layer or a barrier layer) for a non-magnetic layer are known as magnetoresistive effect elements. Magnetoresistive effect elements can be applied to magnetic sensors, high-frequency components, magnetic heads and non-volatile random access memories (MRAMs).

MRAMs are memory elements in which magnetoresistive effect elements are integrated. An MRAM reads and writes data utilizing the characteristics in which a resistance of a magnetoresistive effect element changes in response to change in directions of magnetizations of two ferromagnetic layers with a non-magnetic layer interposed therebetween in the magnetoresistive effect element. For example, the direction of the magnetization of the ferromagnetic layer is controlled utilizing a magnetic field generated by an electric current. In addition, for example, the direction of the magnetization of the ferromagnetic layer is controlled utilizing a spin transfer torque (STT) generated by causing an electric current to flow in a lamination direction of the magnetoresistive effect element.

When the direction of the magnetization of the ferromagnetic layer is rewritten utilizing an STT, an electric current is caused to flow in the lamination direction of the magnetoresistive effect element. A write current will cause deterioration in characteristics of the magnetoresistive effect element.

In recent years, methods which do not require an electric current to flow in a lamination direction of a magnetoresistive effect element during writing have attracted attention. One of such methods is a writing method utilizing a spin orbit torque (SOT) (for example, Patent Document 1). An SOT is generated by a spin current induced due to a spin orbit interaction or a Rashba effect in interfaces of dissimilar materials. An electric current for inducing an SOT into a magnetoresistive effect element flows in a direction intersecting the lamination direction of the magnetoresistive effect element. That is, there is no need for an electric current to flow in the lamination direction of the magnetoresistive effect element, and therefore it is expected that life-spans of magnetoresistive effect elements will be extended.

Patent Document

SUMMARY

In a magnetoresistive effect element using a spin orbit torque (SOT), if an electric current density of a write current flowing in a spin orbit torque wiring becomes equal to or higher than a predetermined value, the magnetization of a ferromagnetic layer is reversed. An electric current density of a write current at which the magnetization of the ferromagnetic layer is reversed is referred to as a reversal current density. In order to enhance the efficiency of writing a signal in a magnetoresistive effect element, it is required to reduce the reversal current density. In order to reduce the reversal current density, it is required to cause a spin orbit torque induced due to a Rashba effect in interfaces to efficiently act on the ferromagnetic layer.

The present disclosure is made in consideration of the foregoing circumstances, and an object thereof is to provide a magnetic element and a magnetic memory capable of causing a spin orbit torque induced due to a Rashba effect in interfaces to efficiently act on a ferromagnetic layer.

In order to resolve the foregoing problems, the present invention provides the following means.

This magnetic element includes a spin orbit torque wiring and a laminate. The laminate comes into contact with the spin orbit torque wiring and includes a first ferromagnetic layer. The spin orbit torque wiring includes three or more layers. Combinations of materials of the layers in the spin orbit torque wiring are asymmetric in a lamination direction. A sequence of material types in which the materials of the layers of the spin orbit torque wiring are arranged from a first surface in contact with the laminate toward a second surface on a side opposite to the first surface differs from a sequence of material types in which the materials of the layers of the spin orbit torque wiring are arranged from the second surface toward the first surface.

The magnetic element and the magnetic memory according to the present disclosure can cause a spin orbit torque induced due to a Rashba effect in interfaces to efficiently act on a ferromagnetic layer.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present embodiment will be described in detail suitably with reference to the drawings. In the drawings used in the following description, in order to make characteristics easy to understand, characteristic portions may be shown in an enlarged manner for the sake of convenience, and dimensional ratios or the like of each constituent element may differ from actual values thereof. Materials, dimensions, and the like shown in the following description are merely exemplary examples. The present invention is not limited thereto and can be suitably changed and performed within a range in which the effects of the present invention are exhibited.

First, directions will be defined. One direction on a surface of a substrate Sub which will be described below (refer toFIG.2) will be referred to as an x direction, and a direction orthogonal to the x direction will be referred to as a y direction. For example, the x direction is a longitudinal direction of a spin orbit torque wiring20. A z direction is a direction orthogonal to the x direction and the y direction. The z direction is an example of a lamination direction in which the layers are laminated. Hereinafter, a positive z direction may be expressed as “upward”, and a negative z direction may be expressed as “downward”. The upward and downward directions do not necessarily match the direction in which the force of gravity is applied.

In this specification, for example, “extending in the x direction” denotes that the dimension in the x direction is larger than the smallest dimension of the dimensions in the x direction, the y direction, and the z direction. The same applies to cases of extending in other directions. In addition, in this specification, “connection” is not limited to the case of being physically connected. For example, “connection” is not limited to the case where two layers physically come into contact with each other, and it also includes a case where two layers are connected to each other with a different layer interposed therebetween. In addition, in this specification, “connection” also includes electrical connection. In addition, in this specification, “facing” denotes a relationship between two layers facing each other, and the two layers may be in contact with each other and may face each other with a different layer interposed therebetween.

First Embodiment

FIG.1is a view of a constitution of a magnetic memory200according to a first embodiment. The magnetic memory200includes a plurality of magnetoresistive effect elements100, a plurality of write wirings WL, a plurality of common wirings CL, a plurality of read wirings RL, a plurality of first switching elements Sw1, a plurality of second switching elements Sw2, and a plurality of third switching elements Sw3. For example, in the magnetic memory200, the magnetoresistive effect elements100are arrayed in a matrix shape. The magnetoresistive effect element100is an example of a magnetic element.

Each of the write wirings WL electrically connects a power source to one or more magnetoresistive effect elements100. Each of the common wirings CL is a wiring used during both writing and reading of data. Each of the common wirings CL electrically connects a reference potential to one or more magnetoresistive effect elements100. For example, the reference potential is a ground potential. The common wiring CL may be provided in each of the plurality of magnetoresistive effect elements100or may be provided across the plurality of magnetoresistive effect elements100. Each of the read wirings RL electrically connects the power source to one or more magnetoresistive effect elements100. The power source is connected to the magnetic memory200when in use.

Each of the magnetoresistive effect elements100is electrically connected to each of the first switching element Sw1, the second switching element Sw2, and the third switching element Sw3. The first switching element Sw1is connected between the magnetoresistive effect element100and the write wiring WL. The second switching element Sw2is connected between the magnetoresistive effect element100and the common wiring CL. The third switching element Sw3is connected to the read wiring RL across the plurality of magnetoresistive effect elements100.

If a predetermined first switching element Sw1and a predetermined second switching element Sw2are turned on, a write current flows between the write wiring WL and the common wiring CL connected to a predetermined magnetoresistive effect element100. Data is written in the predetermined magnetoresistive effect element100in response to a flow of a write current. If a predetermined second switching element Sw2and a predetermined third switching element Sw3are turned on, a read current flows between the common wiring CL and the read wiring RL connected to a predetermined magnetoresistive effect element100. Data is read from the predetermined magnetoresistive effect element100in response to a flow of a read current.

The first switching elements Sw1, the second switching elements Sw2, and the third switching elements Sw3are elements controlling flows of an electric current. For example, the first switching elements Sw1, the second switching elements Sw2, and the third switching elements Sw3are elements such as transistors, ovonic threshold switches (OTSs) utilizing phase change in crystal layer, elements such as metal-insulator transition (MIT) switches utilizing change in band structure, elements such as Zener diodes and avalanche diodes utilizing a breakdown voltage, or elements whose conductivity changes in response to change in atom position.

In the magnetic memory200shown inFIG.1, the third switching element Sw3is shared by the magnetoresistive effect elements100connected to the same read wiring RL. The third switching element Sw3may be provided in each of the magnetoresistive effect elements100. In addition, the third switching element Sw3may be provided in each of the magnetoresistive effect elements100, and the first switching element Sw1or the second switching element Sw2may be shared by the magnetoresistive effect elements100connected to the same wiring.

FIG.2is a cross-sectional view of a characteristic portion of the magnetic memory200according to the first embodiment.FIG.2is a cross section of the magnetoresistive effect element100cut along an xz plane passing through the center of the width of the spin orbit torque wiring20(which will be described below) in the y direction.

The first switching element Sw1and the second switching element Sw2shown inFIG.2are transistors Tr. The third switching element Sw3is electrically connected to the read wiring RL and is located, for example, at a different position in the y direction inFIG.2. For example, the transistor Tr is a field effect-type transistor having a gate electrode G, a gate insulating film GI, and a source S and a drain D formed on the substrate Sub. The source S and the drain D are prearranged in accordance with a flow direction of an electric current, and these are in the same region. The positional relationship of the source S and the drain D may be reversed. For example, the substrate Sub is a semiconductor substrate.

The transistors Tr and the magnetoresistive effect element100are electrically connected via a first via wiring30and a second via wiring40. In addition, each of the transistors Tr is connected to the write wiring WL or the common wiring CL via a via wiring W1. Each of the first via wiring30, the second via wiring40, and the via wiring W1extends in the z direction, for example. Each of the first via wiring30, the second via wiring40, and the via wiring W1may be a wiring in which a plurality of columnar bodies are laminated. Each of the first via wiring30, the second via wiring40, and the via wiring W1includes a conductive material.

An area around the magnetoresistive effect element100and the transistors Tr is covered by an insulating layer90. The insulating layer90is an insulating layer for insulating wirings in a multilayer wiring or elements from each other. For example, the insulating layer90is made of silicon oxide (SiOx), silicon nitride (SiNx), silicon carbide (SiC), chromium nitride (CrN), silicon carbonitride (SiCN), silicon oxynitride (SiON), aluminum oxide (Al2O3), zirconium oxide (ZrOx), magnesium oxide (MgO), aluminum nitride (AlN), or the like.

FIG.3is a cross-sectional view of the magnetoresistive effect element100.FIG.3is a cross section of the magnetoresistive effect element100cut along an xz plane passing through the center of the width of the spin orbit torque wiring20in the y direction.FIG.4is a plan view of the magnetoresistive effect element100viewed in the z direction.

For example, the magnetoresistive effect element100includes a laminate10and the spin orbit torque wiring20.

The magnetoresistive effect element100is a magnetic element utilizing a spin orbit torque (SOT) and may be referred to as a spin orbit torque-type magnetoresistive effect element, a spin injection-type magnetoresistive effect element, or a spin current magnetoresistive effect element.

The magnetoresistive effect element100is an element for recording and saving data. The magnetoresistive effect element100records data based on a resistance value of the laminate10in the z direction. The resistance value of the laminate10in the z direction changes when a write current is applied along the spin orbit torque wiring20and spins are injected from the spin orbit torque wiring20to the laminate10. The resistance value of the laminate10in the z direction can be read by applying a read current in the z direction of the laminate10.

The laminate10is connected to the spin orbit torque wiring20. For example, the laminate10shown inFIG.3is laminated on the spin orbit torque wiring20.

The laminate10is a columnar body. For example, the shape of the laminate10in the z direction in a plan view is a circular shape, an oval shape, or a quadrangular shape. For example, the side surfaces of the laminate10are inclined with respect to the z direction.

For example, the laminate10includes a first ferromagnetic layer1, a second ferromagnetic layer2, a non-magnetic layer3, a base layer4, a cap layer5, and a mask layer6. In the laminate10, the resistance value changes in accordance with a difference in a relative angle between magnetizations of the first ferromagnetic layer1and the second ferromagnetic layer2with the non-magnetic layer3interposed therebetween.

For example, the first ferromagnetic layer1faces the spin orbit torque wiring20. The first ferromagnetic layer1may directly come into contact with the spin orbit torque wiring20or may indirectly come into contact with it via the base layer4. For example, the first ferromagnetic layer1is laminated on the spin orbit torque wiring20.

Side surfaces of the first ferromagnetic layer1are inclined. A length L1Aof a first surface1A of the first ferromagnetic layer1on the spin orbit torque wiring20side in the x direction is longer than a length L1Bof a second surface1B on a side opposite to the first surface1A in the x direction. The first surface1A inFIG.3is closer to the substrate Sub than the second surface1B.

Spins are injected into the first ferromagnetic layer1from the spin orbit torque wiring20. The magnetization of the first ferromagnetic layer1receives a spin orbit torque (SOT) due to injected spins, and the orientation direction thereof changes. The first ferromagnetic layer1is referred to as a magnetization free layer.

The first ferromagnetic layer1includes a ferromagnetic body. For example, the ferromagnetic body is a metal selected from the group consisting of Cr, Mn, Co, Fe, and Ni; an alloy including one or more kinds of these metals; an alloy including at least one or more kinds of elements of these metals, B, C, and N; or the like. For example, a ferromagnetic body is Co—Fe, Co—Fe—B, Ni—Fe, a Co—Ho alloy, a Sm—Fe alloy, a Fe—Pt alloy, a Co—Pt alloy, or a CoCrPt alloy.

The first ferromagnetic layer1may include a Heusler alloy. The Heusler alloy includes an intermetallic compound having a chemical composition of XYZ or X2YZ. X is a transition metal element from the Co, Fe, Ni, or Cu groups or a noble metal element on the periodic table. Y is a transition metal from the Mn, V, Cr, or Ti groups or the same kind of element as X. Z is a typical element from Group III to Group V. For example, the Heusler alloy is Co2FeSi, Co2FeGe, Co2FeGa, Co2MnSi, Co2Mn1−aFeaAlbSi1−b, Co2FeGe1−cGac, or the like. The Heusler alloy has a high spin polarizability.

The second ferromagnetic layer2faces the first ferromagnetic layer1with the non-magnetic layer3interposed therebetween. The second ferromagnetic layer2includes a ferromagnetic body. The orientation direction of the magnetization of the second ferromagnetic layer2is less likely to change than that of the magnetization of the first ferromagnetic layer1when a predetermined external force is applied. The second ferromagnetic layer2is referred to as a magnetization fixed layer or a magnetization reference layer. In the laminate10shown inFIG.3, the magnetization fixed layer is located on a side away from the substrate Sub and is referred to as a top pin structure.

A material similar to that constituting the first ferromagnetic layer1is used as a material constituting the second ferromagnetic layer2.

The second ferromagnetic layer2may have a synthetic antiferromagnetic structure (SAF structure). The synthetic antiferromagnetic structure is constituted of two magnetic layers with a non-magnetic layer interposed therebetween. The second ferromagnetic layer2may have two magnetic layers and interposed therebetween a spacer layer. Antiferromagnetic coupling between two ferromagnetic layers makes a coercive force of the second ferromagnetic layer2larger. For example, the ferromagnetic layer is made of IrMn, PtMn, or the like. For example, the spacer layer includes at least one selected from the group consisting of Ru, Ir, and Rh.

The non-magnetic layer3is interposed between the first ferromagnetic layer1and the second ferromagnetic layer2. The non-magnetic layer3includes a non-magnetic body. When the non-magnetic layer3is an insulator (in a case of a tunnel barrier layer), for example, Al2O3, SiO2, MgO, MgAl2O4, or the like can be used as a material thereof. In addition to these, a material or the like in which a part of Al, Si, and Mg is replaced with Zn, Be, or the like can also be used. Among these, since MgO and MgAl2O4are materials capable of realizing a coherent tunnel, spins can be efficiently injected. When the non-magnetic layer3is made of a metal, Cu, Au, Ag, or the like can be used as a material thereof. Moreover, when the non-magnetic layer3is a semiconductor, Si, Ge, CuInSe2, CuGaSe2, Cu(In,Ga)Se2, or the like can be used as a material thereof.

For example, the base layer4is located between the first ferromagnetic layer1and the spin orbit torque wiring20. The base layer4may be omitted.

For example, the base layer4includes a buffer layer and a seed layer. The buffer layer is a layer alleviating lattice mismatch between different crystals. The seed layer enhances crystallinity of a layer laminated on the seed layer. For example, the seed layer is formed on the buffer layer.

For example, the buffer layer is made of Ta (single substance), TaN (tantalum nitride), CuN (copper nitride), TiN (titanium nitride), or NiAl (nickel aluminum). For example, the seed layer is made of Pt, Ru, Zr, a NiCr alloy, or NiFeCr.

The cap layer5is located on the second ferromagnetic layer2. For example, the cap layer5strengthens the magnetic anisotropy of the second ferromagnetic layer2. For example, the cap layer5strengthens the perpendicular magnetic anisotropy of the second ferromagnetic layer2. For example, the cap layer5is made of magnesium oxide, W, Ta, Mo, or the like. For example, the film thickness of the cap layer5is 0.5 nm to 5.0 nm.

The mask layer6is located on the cap layer5. The mask layer6is a part of a hard mask used when the laminate10is processed during manufacturing. The mask layer6also functions as an electrode. For example, the mask layer6includes Al, Cu, Ta, Ti, Zr, NiCr, nitrides (for example, TiN, TaN, or SiN), and oxides (for example, SiO2).

The laminate10may also have a layer other than the first ferromagnetic layer1, the second ferromagnetic layer2, the non-magnetic layer3, the base layer4, the cap layer5, and the mask layer6.

For example, the spin orbit torque wiring20has a longer length in the x direction than in the y direction when viewed in the z direction and extends in the x direction. A write current flows in the x direction along the spin orbit torque wiring20between the first via wiring30and the second via wiring40.

The spin orbit torque wiring20induces a spin current due to a spin orbit interaction and an interfacial Rashba effect and injects spins into the first ferromagnetic layer1. For example, the spin orbit torque wiring20applies enough spin orbit torque (SOT) to the magnetization of the first ferromagnetic layer1to reverse the magnetization of the first ferromagnetic layer1.

A spin Hall effect is a phenomenon in which a spin current is induced in a direction orthogonal to the direction in which an electric current flows based on the spin orbit interaction when an electric current flows. The spin Hall effect is in common with an ordinary Hall effect in that a motion (movement) direction is bent due to motion (movement) of electric charge (electrons). In an ordinary Hall effect, the motion direction of charged particles in motion in a magnetic field is bent due to a Lorentz force. In contrast, in the spin Hall effect, the movement direction of spins is bent simply by movement of electrons (simply by a flow of an electric current) even if no magnetic field is present.

For example, if an electric current flows in the spin orbit torque wiring20, first spins polarized in one direction and second spins polarized in a direction opposite to the first spins are bent due to the spin Hall effect in a direction orthogonal to the direction in which an electric current flows. For example, the first spins polarized in the negative y direction are bent in the positive z direction from the x direction that is a traveling direction thereof, and the second spins polarized in the positive y direction are bent in the negative z direction from the x direction that is a traveling direction thereof.

In a non-magnetic body (a material which is not a ferromagnetic body), the number of electrons in the first spins and the number of electrons in the second spins generated due to the spin Hall effect are equivalent to each other. That is, the number of electrons in the first spins directed in the positive z direction and the number of electrons in the second spins directed in the negative z direction are equivalent to each other. The first spins and the second spins flow in a direction in which uneven distribution of spins is resolved. Since flows of electric charge cancel each other out during movement of the first spins and the second spins in the z direction, the amount of electric current becomes zero. A spin current entailing no electric current is particularly referred to as a pure spin current.

When a flow of electrons in the first spins is expressed as J⬆, a flow of electrons in the second spins is expressed as J⬇, and a spin current is expressed as JS, the spin current is defined as JS=J⬆-J⬇. The spin current JSis generated in the z direction. The first spins are injected into the first ferromagnetic layer1from the spin orbit torque wiring20.

Although the detailed mechanism is not clear, it is said that an interfacial Rashba effect occurs due to breaking of spatial reversal symmetry in an interface between dissimilar materials. In an interface between dissimilar materials, spatial reversal symmetry is broken, and a potential gradient is present in a direction perpendicular to the surface. When an electric current flows along an interface with a potential gradient in such a direction perpendicular to the surface, namely, when electrons are in motion within a two-dimensional plane, an effective magnetic field applies to spins in a direction perpendicular to the motion direction of electrons and an in-plane direction. When directions of spins are aligned in the direction of this effective magnetic field, spin accumulation is occurred in an interface. Further, this spin accumulation diffuses out of the plane, thereby causing spin injection into the first ferromagnetic layer1from the spin orbit torque wiring20.

In order to efficiently inject spins into the first ferromagnetic layer1from the spin orbit torque wiring20, it is required to appropriately utilize the spin orbit interaction and the interfacial Rashba effect.

The spin orbit torque wiring20has a first layer21, a second layer22, and a third layer23. Shown inFIG.3the spin orbit torque wiring20has the third layer23, the second layer22, and the first layer21in this order from the side closer to the substrate Sub. The first layer21comes into contact with the laminate10. The second layer22is interposed between the first layer21and the third layer23in the z direction. An interface I1is located in a boundary between the first layer21and the second layer22, and an interface I2is located in a boundary between the second layer22and the third layer23. The interface I1is an example of a first interface, and the interface I2is an example of a second interface.

Each of the first layer21, the second layer22, and the third layer23includes any of a metal, an alloy, an intermetallic compound, a metal boride, a metal carbide, a metal silicide, a metal phosphide, and a metal nitride having a function of generating a spin current.

For example, each of the first layer21, the second layer22, and the third layer23includes any one selected from the group consisting of a heavy metal having an atomic number of 39 or larger, a metal oxide, a metal nitride, a metal oxynitride, and a topological insulator.

For example, each of the first layer21, the second layer22, and the third layer23includes a non-magnetic heavy metal as a main component. A heavy metal denotes a metal having a specific gravity equal to or greater than that of yttrium (Y). For example, a non-magnetic heavy metal is a non-magnetic metal having a large atomic number, such as an atomic number of 39 or larger, and has d electrons or f electrons in an outermost shell. In a non-magnetic heavy metal, a stronger spin orbit interaction occurs than in other metals. The spin Hall effect occurs due to the spin orbit interaction so that spins are likely to be unevenly distributed within the spin orbit torque wiring20and the spin current JSis likely to be generated.

Each of the first layer21, the second layer22, and the third layer23may include a magnetic material. However, in order to prevent the first ferromagnetic layer1and the first layer21from being magnetically coupled, it is preferable that the first layer21be a non-magnetic layer. In addition, each of the first layer21, the second layer22, and the third layer23may be a topological insulator.

In addition, it is preferable that at least one of the first layer21, the second layer22, and the third layer23have an impurity concentration of 3 atm % or lower. In addition, it is preferable that all the first layer21, the second layer22, and the third layer23have an impurity concentration of 3 atm % or lower. If these layers include fewer impurities, a probability of occurrence of transposition inside the spin orbit torque wiring decreases so that the interface between the layers becomes flat. If flatness of the interface is high, the interfacial Rashba effect occurs effectively.

The constituent materials of the first layer21, the second layer22, and the third layer23are different from each other. For this reason, in the spin orbit torque wiring20, combinations of the materials of the layers are asymmetric in the lamination direction. A sequence of material types in which the materials of the layers of the spin orbit torque wiring20are arranged from a first surface toward a second surface differs from a sequence of material types in which the materials of the layers of the spin orbit torque wiring20are arranged from the second surface toward the first surface. The first surface is a surface of the spin orbit torque wiring20in contact with the laminate10. The second surface is a surface on a side opposite to the first surface.

If the constituent materials differ from each other, it is possible to curb a situation in which a spin current generated due to the interfacial Rashba effect in the interface I1and a spin current generated due to the interfacial Rashba effect in the interface I2cancel each other out. For example, when the first layer21and the third layer23having the second layer22interposed therebetween are made of the same material, a spin current generated due to the interfacial Rashba effect in the interface I1and a spin current generated due to the interfacial Rashba effect in the interface I2cancel each other out.

It is more preferable that the combination of elements respectively included in the first layer21, the second layer22, and the third layer23conform with being any one of the following. Examples of (the first layer21, the second layer22, and the third layer23) preferably include (W, Cr, and Mo), (W, Mg, and Mo), (Pt, Cu, and Ti), (W, Mo, and Ta), (W, Mg, and Ta), (W, Cr, and Ta), (W, Cu, and Ta), (Mg, Cr, and Mo), (Cr, Mg, and Mo), (W, Fe, and Ta), (W, Fe, and Mo), (W, Mo, and Fe), (Mg—Al—O, W, and Mo), (Mg—Al—O, Pt, and Ti), (W, Mo, and Ta—N), and (Pt, Ti, and Ta—N). In addition, it is preferable that the first layer of the spin orbit torque wiring20in contact with the laminate10be a non-magnetic layer.

It is preferable that the interface I1and the interface I2be closer to the first ferromagnetic layer1than the center of the spin orbit torque wiring20in the z direction. If the interface I1and the interface I2are closer to the first ferromagnetic layer1, it is possible to reduce a loss of spins generated in these interfaces I1and I2until they reach the first ferromagnetic layer1.

The interface I1and the interface I2have different areas. For example, a length LI1of the interface I1in the x direction is shorter than a length LI2of the interface I2in the x direction. For example, a width WI1of the interface I1in the y direction is shorter than a width WI2of the interface I2in the y direction. InFIG.4, an example in which the interface I1and the interface I2differ from each other in length in the x direction and the length in the y direction has been described, but they may differ in only the length in the x direction or in only the length in the y direction. If the interface I1and the interface I2have different sizes, it is possible to curb a situation in which a spin current generated due to the interfacial Rashba effect in the interface I1and a spin current generated due to the interfacial Rashba effect in the interface I2cancel each other out.

FIG.5is an enlarged view of a characteristic portion of a spin orbit torque wiring according to the first embodiment.FIG.5schematically shows an arrangement of atoms A in the first layer21, the second layer22, and the third layer23.

It is preferable that at least one of the interface I1and the interface I2have 90% or more of a portion in which an interface roughness is two atomic layers or smaller. It is more preferable that the interface I1have 90% or more of a portion in which an interface roughness R1is two atomic layers or smaller. In addition, it is particularly preferable that both the interface I1and the interface I2have 90% or more of a portion in which the interface roughness R1and an interface roughness R2are two atomic layers or smaller.

Here, definitions of the interface roughness R1and the interface roughness R2in the present embodiment will be described. When the interface roughness R1and the interface roughness R2are evaluated, an interface at a position overlapping the first ferromagnetic layer1when viewed in the z direction is measured using a transmission electron microscope, and the array of the atoms A is confirmed. This is because the interface I1and the interface I2at positions overlapping the first ferromagnetic layer1when viewed in the z direction have a strong influence on spin injection into the first ferromagnetic layer1.

More specifically, the interface I1and the interface I2at positions overlapping the first ferromagnetic layer1when viewed in the z direction are evaluated along a width of 10 nm in the x direction. For example, when the width of the first surface1A of the first ferromagnetic layer1in the x direction is 50 nm, the interfaces I1and I2are divided into five parts each having a width of 10 nm, and they are individually measured. For example, when the width of the first surface1A of the first ferromagnetic layer1in the x direction is 45 nm, the interfaces I1and I2are divided into four parts each having a width of 10 nm at equal intervals, and they are individually measured.

The interface roughness R1is obtained as a displacement amount of the atoms A in the interface I1. The interface roughness R2is obtained as a displacement amount of the atoms A in the interface I2. A portion in which the interface roughness in the interface is two atomic layers or smaller is a portion in which deviation of atoms is within a range of two atoms. For example, as described above, when five parts each having a width of 10 nm are measured, the average value of results of the five parts is obtained. If a portion in which the interface roughness R1and the interface roughness R2are two atomic layers or smaller is 90% or more, it can be said that the interfaces I1and I2are basically flat excluding local spikes, defects, or the like.

For example, the interface roughness R2of the interface I2is smaller than the interface roughness R1of the interface I1. That is, the interface I2is flatter than the interface I1. The interface I2is farther from the first ferromagnetic layer1than the interface I1. If the interface I2is flat and there is a large amount of spin current generated due to the interfacial Rashba effect in the interface I2, spins from the interface I2can be sufficiently delivered to the first ferromagnetic layer1.

The first layer21, the second layer22, and the third layer23are epitaxially grown. Here, an example in which these three layers are epitaxially grown has been described, but the first layer21and the second layer22may be epitaxially grown, or the second layer22and the third layer23may be epitaxially grown.

Whether or not these layers are epitaxially grown can be confirmed by the fact that the atoms A are consecutively arrayed in an image of a transmission electron microscope (TEM). When the first layer21, the second layer22, and the third layer23are epitaxially grown, as shown inFIG.5, if an array of the atoms A is confirmed in order from the lower layer, it is possible to draw a line L in which atoms are arranged in a row. When these layers are not epitaxially grown, obvious distortion can be confirmed and the line L is disconnected on the way from the third layer23to the first layer21.

For example, the lattice misfit rate in the first layer21and the second layer22is lower than 5%. This lattice misfit rate in the interface is obtained by (“Lattice constant a21of first layer21”−“Lattice constant a22of second layer22”)/“Lattice constant a22of second layer22”.

In addition, for example, the lattice misfit rate in the second layer22and the third layer23is lower than 5%. This lattice misfit rate in the interface is obtained by (“Lattice constant a22of second layer22”−“Lattice constant a23of third layer23”)/“Lattice constant a23of third layer23”.

If the lattice misfit rate in each interface is within the foregoing range, crystallinity of each layer increases so that the flat interfaces I1and I2can be obtained.

Next, a method for manufacturing the magnetoresistive effect element100will be described. The magnetoresistive effect element100is formed by a laminating step for each layer and a processing step of processing a part of each layer into a predetermined shape. Each layer can be laminated using a sputtering method, a chemical vapor deposition (CVD) method, an electron beam evaporation method (EB evaporation method), an atom laser deposition method, or the like. Each layer can be processed using photolithography or the like.

First, a part of the insulating layer90is formed, and an opening is formed at a predetermined position. Next, the inside of the opening is filled with a conductor, and the first via wiring30and the second via wiring40are formed.

Next, surfaces of the first via wiring30, the second via wiring40, and the insulating layer90are subjected to chemical mechanical polishing (CMP). Next, a layer which will serve as the third layer23, a layer which will serve as the second layer22, and a layer which will serve as the first layer21are formed on these surfaces in this order. Every time each of these layers is laminated, the surface thereof is subjected to chemical mechanical polishing. In addition, every time each of these layers is laminated, the surface thereof is subjected to plasma treatment. By performing the foregoing treatment, the interface roughness of the interface I1between the first layer21and the second layer22and the interface I2between the second layer22and the third layer23can be set within a predetermined range.

Next, the layer which will serve as the third layer23, the layer which will serve as the second layer22, and the layer which will serve as the first layer21are processed into predetermined shapes, and the spin orbit torque wiring20is obtained. Next, an area around the spin orbit torque wiring20is covered the insulating layer. Further, a part of the covered insulating layer is subjected to chemical mechanical polishing. By performing chemical mechanical polishing, an upper surface of the spin orbit torque wiring20is exposed and flattened.

Next, on the spin orbit torque wiring20, a base layer, a ferromagnetic layer, a non-magnetic layer, a ferromagnetic layer, and a cap layer are laminated in this order. Further, the mask layer6is formed in a portion of a part of the cap layer. Next, the laminate10is obtained by processing each of the laminated layers into a predetermined shape via the mask layer6. Further, the magnetoresistive effect element100is obtained by covering the area around the laminate10with an insulating layer.

In the magnetoresistive effect element100according to the first embodiment, since the materials of the first layer21, the second layer22, and the third layer23are different from each other, it is possible to curb a situation in which spins generated in the interface I1and spins generated in the interface I2cancel each other out. In addition, since the interface I1and the interface I2have different areas, it is possible to further curb a situation in which spins generated in the interface I1and spins generated in the interface I2cancel each other out. In addition, since the interface roughness R1and the interface roughness R2of the interface I1and the interface I2are within a predetermined range, a spin current due to the interfacial Rashba effect can be more efficiently generated in each of the interface I1and the interface I2.

First Modification Example

FIG.6is a cross-sectional view of a magnetoresistive effect element101according to a first modification example of the first embodiment. In the magnetoresistive effect element101according to the first modification example of the first embodiment, the same reference signs are applied to constituents similar those of the magnetoresistive effect element100, and description thereof will be omitted.

The magnetoresistive effect element101according to the first modification example of the first embodiment differs from the magnetoresistive effect element100in laminating order of the laminate10and the spin orbit torque wiring20. The spin orbit torque wiring20is laminated on the laminate10.

The laminate10has the base layer4, the second ferromagnetic layer2, the non-magnetic layer3, the first ferromagnetic layer1, and the cap layer5in this order from the side closer to the substrate Sub. In the magnetoresistive effect element101, the second ferromagnetic layer2(magnetization fixed layer) is closer to the substrate Sub than the first ferromagnetic layer1and is referred to as a bottom pin structure. The length L1Aof the first surface1A of the first ferromagnetic layer1on the spin orbit torque wiring20side in the x direction is shorter than the length L1Bof the second surface1B on a side opposite to the first surface1A in the x direction.

The spin orbit torque wiring20shown inFIG.6has the first layer21, the second layer22, and the third layer23in this order from the side closer to the substrate Sub.

For example, the length LI1of the interface I1in the x direction is longer than the length LI2of the interface I2in the x direction. If the interface I1and the interface I2have different sizes, it is possible to curb a situation in which a spin current generated due to the interfacial Rashba effect in the interface I1and a spin current generated due to the interfacial Rashba effect in the interface I2cancel each other out. In addition, the interface I1and the interface I2may have different widths in the y direction. For example, the width Wnof the interface I1in the y direction may be longer than the width WI2of the interface I2in the y direction.

The interface roughness R1of the interface I1is smaller than the interface roughness R2of the interface I2. That is, the interface I1is flatter than the interface I2. The interface I1is closer to the first ferromagnetic layer1than the interface I2. For this reason, spins generated due to the interfacial Rashba effect in the interface I1are less likely to scatter than spins generated due to the interfacial Rashba effect in the interface I2until they reach the first ferromagnetic layer1. If the interface I1is flat, a large amount of spins are generated in the interface I1so that more spins can be injected into the first ferromagnetic layer1.

The magnetoresistive effect element101according to the first modification example of the first embodiment exhibits effects similar to those of the magnetoresistive effect element100.

Second Modification Example

FIG.7is a cross-sectional view of a magnetization rotation element102according to a second modification example of the first embodiment. The magnetoresistive effect element100inFIG.1is replaced with the magnetization rotation element102. The magnetization rotation element102differs from the magnetoresistive effect element100in that the second ferromagnetic layer2and the non-magnetic layer3are not provided. The magnetization rotation element102is an example of a magnetic element.

For example, in the magnetization rotation element102, light is incident on the first ferromagnetic layer1, and light reflected by the first ferromagnetic layer1is evaluated. If the orientation direction of the magnetization changes due to a magnetic Kerr effect, the deflection state of reflected light changes. For example, the magnetization rotation element102can be used as an optical element such as a video display device, for example, utilizing the difference in light deflection state.

Furthermore, the magnetization rotation element102can also be utilized alone as an anisotropic magnetic sensor, an optical element utilizing a magnetic Faraday effect, or the like.

The magnetization rotation element102according to the second modification example is obtained by simply removing the non-magnetic layer3and the second ferromagnetic layer2from the magnetoresistive effect element100, and it is possible to achieve effects similar to those of the magnetoresistive effect element100according to the first embodiment.

Second Embodiment

FIG.8is a cross-sectional view of a magnetoresistive effect element110according to a second embodiment. For example, the magnetoresistive effect element110includes the laminate10and a spin orbit torque wiring60. In the magnetoresistive effect element110, the constitution of the spin orbit torque wiring60differs from that of the spin orbit torque wiring20according to the first embodiment.

FIG.9is a cross-sectional view of the spin orbit torque wiring60according to the second embodiment. The spin orbit torque wiring60differs from the spin orbit torque wiring20according to the first embodiment in having four or more layers. For example, the spin orbit torque wiring60may be constituted of four layers or may be constituted of five layers.

For example, the spin orbit torque wiring60has a longer length in the x direction than in the y direction when viewed in the z direction and extends in the x direction. For example, the length of a first surface60A of the spin orbit torque wiring60in the x direction is shorter than the length of a second surface60B of the spin orbit torque wiring60in the x direction. The first surface60A is a surface of the spin orbit torque wiring60in contact with the laminate10. The second surface60B is a surface of the spin orbit torque wiring60on a side opposite to the first surface60A. A write current flows in the x direction along the spin orbit torque wiring60between the first via wiring30and the second via wiring40.

The spin orbit torque wiring60shown inFIG.9has a first layer601, a second layer602, a third layer603, and so on to n layers (n is an integer of 4 or larger), such as an n−2th layer60n-2, an n−1th layer60n-1, and an nth layer60n, in this order from the side closer to the first surface60A. In addition, the spin orbit torque wiring60has n−1 interfaces. Hereinafter, they will be referred to as a first interface I1, a second interface I2, a third interface I3, so on to an n−2th interface In-2, and an n−1th interface In-1in this order from the side closer to the first surface60A.

The position of an interface is obtained by performing measurement in a thickness direction using energy dispersive X-ray spectroscopy (EDS). For example, if a first material included in the first layer601is subjected to EDS measurement, an intensity distribution having a peak near the center of the first layer601in the z direction is obtained. Similarly, if a second material included in the second layer602is subjected to EDS measurement, an intensity distribution having a peak near the center of the second layer602in the z direction is obtained. A position where a curve indicating the intensity distribution of the first material and a curve indicating the intensity distribution of the second material intersect corresponds to the first interface I1.

Each of the layers constituting the spin orbit torque wiring60includes any of a metal, an alloy, an intermetallic compound, a metal boride, a metal carbide, a metal silicide, a metal phosphide, and a metal nitride having a function of generating a spin current. Materials which can be used for each of the layers constituting the spin orbit torque wiring60are similar to those in the spin orbit torque wiring20.

For example, when the spin orbit torque wiring60has a four-layer structure, it is preferable that a combination of elements respectively included in a first layer, a second layer, a third layer, and a fourth layer conform with being any one of the following. Here, the first layer, the second layer, the third layer, and the fourth layer are closer to the laminate10in this order. The combination of elements respectively included in the first layer, the second layer, the third layer, and the fourth layer will be expressed as (the first layer, the second layer, the third layer, and the fourth layer).

For example, when the spin orbit torque wiring60has a five-layer structure, it is preferable that a combination of elements respectively included in a first layer, a second layer, a third layer, a fourth layer, and a fifth layer conform with being any one of the following. Here, the first layer, the second layer, the third layer, the fourth layer, and the fifth layer are closer to the laminate10in this order. The combination of elements respectively included in the first layer, the second layer, the third layer, the fourth layer, and the fifth layer will be expressed as (the first layer, the second layer, the third layer, the fourth layer, and the fifth layer).

In the spin orbit torque wiring60, the combinations of the materials of the layers are asymmetric in the z direction. In the spin orbit torque wiring60, the sequence of material types in which the materials of the layers of the spin orbit torque wiring60are arranged from the first surface60A toward the second surface60B differs from the sequence of material types in which the materials of the layers of the spin orbit torque wiring60are arranged from the second surface60B toward the first surface60A.

The constitution will be described by presenting specific materials. For example, a case where the spin orbit torque wiring60is constituted of four layers in which the first layer601is made of tungsten, the second layer602is made of copper, the third layer603is made of tungsten, and a fourth layer604is made of tantalum will be described as an example. In this case, the sequence of material types in which the materials of the layers of the spin orbit torque wiring60are arranged from the first surface60A toward the second surface60B has “W, Cu, W, and Ta”, and the sequence of material types in which the materials of the layers of the spin orbit torque wiring60are arranged from the second surface60B toward the first surface60A has “Ta, W, Cu, and W”. The sequences of material types “W, Cu, W, and Ta” and “Ta, W, Cu, and W” do not match. That is, in this example, in the spin orbit torque wiring60, the combinations of the materials of the layers are asymmetric in the z direction.

Similarly, for example, a case where the spin orbit torque wiring60is constituted of eight layers in which the first layer601is made of tantalum, the second layer602is made of tungsten, the third layer603is made of copper, the fourth layer604is made of molybdenum, a fifth layer605is made of vanadium, a sixth layer606is made of copper, a seventh layer607is made of tungsten, and an eighth layer608is made of cobalt will be described as an example. In this case, the sequence of material types in which the materials of the layers of the spin orbit torque wiring60are arranged from the first surface60A toward the second surface60B has “Ta, W, Cu, Mo, V, Cu, W, and Co”, and the sequence of material types in which the materials of the layers of the spin orbit torque wiring60are arranged from the second surface60B toward the first surface60A has “Co, W, Cu, V, Mo, Cu, W, and Ta”. The sequences of material types “Ta, W, Cu, Mo, V, Cu, W, and Co” and “Co, W, Cu, V, Mo, Cu, W, and Ta” do not match. That is, in this example as well, in the spin orbit torque wiring60, the combinations of the materials of the layers are asymmetric in the z direction.

In contrast, for example, a case where the spin orbit torque wiring60is constituted of five layers in which the first layer601is made of tungsten, the second layer602is made of copper, the third layer603is made of tungsten, the fourth layer604is made of copper, and the fifth layer605is made of tungsten will be described as an example. In this case, the sequence of material types in which the materials of the layers of the spin orbit torque wiring60are arranged from the first surface60A toward the second surface60B has “W, Cu, W, Cu, and W”, and the sequence of material types in which the materials of the layers of the spin orbit torque wiring60are arranged from the second surface60B toward the first surface60A has “W, Cu, W, Cu, and W”. The sequences of material types “W, Cu, W, Cu, and W” and “W, Cu, W, Cu, and W” match. That is, in this example, in the spin orbit torque wiring60, the combinations of the materials of the layers are symmetric in the z direction.

If the combinations of the materials of the layers in the spin orbit torque wiring60are asymmetric in the z direction, the spins generated due to the Rashba effect in the interface between the layers can be efficiently injected into the first ferromagnetic layer1. This is because canceling out between spins generated due to the Rashba effect in the interfaces can be curbed.

For example, based on an example of the case where the spin orbit torque wiring60is constituted of five layers in which the first layer601is made of tungsten, the second layer602is made of copper, the third layer603is made of tungsten, the fourth layer604is made of copper, and the fifth layer605is made of tungsten, an example in which spins generated due to the Rashba effect in the interfaces cancel each other out will be described.

In the interface I1between the first layer601and the second layer602, the Rashba effect occurs due to interfaces of dissimilar materials such as tungsten and copper. Similarly, in the interface I2between the second layer602and the third layer603, the Rashba effect occurs due to interfaces of dissimilar materials such as copper and tungsten. If two layers are arranged from the first surface60A toward the second surface60B with the interface I1interposed therebetween, there are “W and Cu”, and if two layers are arranged from the first surface60A toward the second surface60B with the interface I2interposed therebetween, there are “Cu and W”. That is, the interface I1and the interface I2are constituted of a pair made of the same material, and simply the order is reversed. In this case, spins generated in the interface I1due to the Rashba effect and spins generated in the interface I2due to the Rashba effect are opposite to each other in sign of direction and have the same magnitude. Namely, spins generated in the interface I1and spins generated in the interface I2cancel each other out.

Similarly, spins generated in the interface I3between the third layer603and the fourth layer604due to the Rashba effect and spins generated in an interface I4between the fourth layer604and the fifth layer605due to the Rashba effect also cancel each other out.

In contrast, if the combinations of the materials of the layers in the spin orbit torque wiring60are asymmetric in the z direction, all spins generated due to the Rashba effect in the interfaces do not cancel each other out.

In addition, it is preferable that the degree of asymmetry in the spin orbit torque wiring60be 0.2 or higher. The degree of asymmetry is obtained by dividing the number of asymmetric interfaces in the spin orbit torque wiring60by the total number of interfaces in the spin orbit torque wiring60. The asymmetric interfaces are interfaces which remain after subtracting paired interfaces from the interfaces in the spin orbit torque wiring60.

The sequence of material types in which the material types of adjacent layers are arranged from the first surface60A toward the second surface60B with one of the paired interfaces interposed therebetween matches the sequence of material types in which the material types of adjacent layers are arranged from the second surface60B toward the first surface60A with the other of the paired interfaces interposed therebetween.

For example, the degree of asymmetry will be obtained based on an example of the case where the spin orbit torque wiring60is constituted of five layers in which the first layer601is made of tungsten, the second layer602is made of copper, the third layer603is made of tungsten, the fourth layer604is made of copper, and the fifth layer605is made of tantalum.

In this example, the total number of interfaces in the spin orbit torque wiring60is four. The sequence of material types in which the material types of two layers are arranged with the first interface I1interposed therebetween from the first surface60A toward the second surface60B has “W and Cu” and the sequence of material types in which the material types of two layers are arranged with the second interface I2interposed therebetween from the second surface60B toward the first surface60A has “W and Cu”, and therefore they match. For this reason, in this example, the first interface I1and the second interface I2are paired interfaces.

In addition, the sequence of material types in which the material types of two layers are arranged with the third interface I3interposed therebetween from the first surface60A toward the second surface60B has “W and Cu”. The third interface I3can also be paired up with the second interface I2. However, since the second interface I2is paired up with the first interface I1and cannot be paired up twice. For this reason, in this example, the third interface I3corresponds to an asymmetric interface.

In addition, the sequence of material types in which the material types of two layers are arranged with the fourth interface I4interposed therebetween from the first surface60A toward the second surface60B has “Cu and Ta”. The fourth interface I4cannot be paired up with any interface. For this reason, in this example, the fourth interface I4corresponds to an asymmetric interface.

In this example, there are two asymmetric interfaces. Therefore, the degree of asymmetry in this example becomes “Number of asymmetric interfaces”/“Total number of interfaces”=2/4=0.5.

Similarly, for example, the degree of asymmetry will be obtained based on an example of the case where the spin orbit torque wiring60is constituted of seven layers in which the first layer601is made of tantalum, the second layer602is made of tungsten, the third layer603is made of copper, the fourth layer604is made of molybdenum, the fifth layer605is made of tungsten, the sixth layer606is made of tantalum, and the seventh layer607is made of vanadium.

In this example, the total number of interfaces in the spin orbit torque wiring60is six. The sequence of material types in which the material types of two layers are arranged with the first interface I1interposed therebetween from the first surface60A toward the second surface60B has “Ta and W” and the sequence of material types in which the material types of two layers are arranged with a fifth interface I5interposed therebetween from the second surface60B toward the first surface60A has “Ta and W”, and therefore they match. For this reason, in this example, the first interface I1and the fifth interface I5are paired interfaces. In this manner, the paired interfaces may not be adjacent to each other. When the paired interfaces are not adjacent to each other, there is an asymmetric interface between two interfaces constituting paired interfaces in the Z direction.

The sequence of material types in which the material types of two layers are arranged with the second interface I2interposed therebetween from the first surface60A toward the second surface60B has “W and Cu”. The sequence of material types in which the material types of two layers are arranged with the third interface I3interposed therebetween from the first surface60A toward the second surface60B has “Cu and Mo”. The sequence of material types in which the material types of two layers are arranged with the fourth interface I4interposed therebetween from the first surface60A toward the second surface60B has “Mo and W”. The sequence of material types in which the material types of two layers are arranged with a sixth interface I6interposed therebetween from the first surface60A toward the second surface60B has “Ta and V”. These interfaces cannot be paired up with any interface. For this reason, in this example, each of the second interface I2, the third interface I3, the fourth interface I4, and the sixth interface I6corresponds to an asymmetric interface.

In this example, there are four asymmetric interfaces. Therefore, the degree of asymmetry in this example becomes “Number of asymmetric interfaces”/“Total number of interfaces”=4/6=0.667.

Spins generated due to the Rashba effect in the asymmetric interfaces do not completely cancel out spins generated in other interfaces. If the degree of asymmetry in the spin orbit torque wiring60is 0.2 or higher, canceling out between spins generated due to the interfacial Rashba effect in the interfaces can be further curbed.

FIG.10is a view showing a relationship between a degree of asymmetry of the spin orbit torque wiring and a spin Hall angle of the spin orbit torque wiring. The spin Hall angle is one of indicators for strength of the spin Hall effect and indicates conversion efficiency of a spin current generated with respect to an electric current flowing along the wiring. The larger the spin Hall angle, the higher the conversion efficiency of a spin current. As shown inFIG.10, if the degree of asymmetry exceeds 0.2, the increasing degree of the spin Hall angle becomes stronger.

In addition, paired interfaces of a plurality of interfaces have different areas. For example, when the first interface I1and the second interface I2are paired interfaces, the interface I1and the interface I2have different areas. For example, one of the paired interfaces (for example, the interface I1) may have a longer length in the x direction than the other of the paired interfaces (for example, the interface I2). In addition, for example, one of the paired interfaces (for example, the interface I1) may have a longer width in the y direction than the other of the paired interfaces (for example, the interface I2). In addition, for example, one of the paired interfaces (for example, the interface I1) may have a longer length in the x direction and a longer width in the y direction than the other of the paired interfaces (for example, the interface I2). If the paired interfaces have different areas, it is possible to curb a situation in which spin currents generated due to the interfacial Rashba effect in the interfaces cancel each other out.

In addition, each of a plurality of interfaces may have a different area. For example, each of the first interface I1, the second interface I2, the third interface I3, so on to the n−2th interface In-2, and the n−1th interface In−1may have a different area. When each of the interfaces has a different area, it is possible to further curb a situation in which spin currents generated due to the interfacial Rashba effect in the interfaces cancel each other out.

FIG.11is an enlarged view of a characteristic portion of the spin orbit torque wiring60according to the second embodiment.FIG.11schematically shows an arrangement of the atoms A in an mth layer60m, and an m+1th layer60m+1.

For example, it is preferable that at least one interface of the interfaces included in the spin orbit torque wiring60have 90% or more of a portion in which the interface roughness is two atomic layers or smaller. In addition, it is preferable that all the interfaces included in the spin orbit torque wiring60have 90% or more of a portion in which the interface roughness is two atomic layers or smaller.

The definition of an interface roughness R is similar to that in the first embodiment. First, an interface Imat a position overlapping the first ferromagnetic layer1when viewed in the z direction is evaluated along a width of 10 nm in the x direction. For example, when the width of the first ferromagnetic layer1in the x direction is 50 nm, the interface Im, is divided into five parts each having a width of 10 nm, and they are individually measured. For example, when the width of the first ferromagnetic layer1in the x direction is 45 nm, the interface Imis divided into four parts each having a width of 10 nm at equal intervals, and they are individually measured.

The interface roughness R is obtained as a displacement amount of the atoms A in the interface Im. A portion in which the interface roughness in the interface is two atomic layers or smaller is a portion in which deviation of atoms is within a range of two atoms. For example, as described above, when five parts each having a width of 10 nm are measured, the average value of results of the five parts is obtained. If a portion in which the interface roughness R is two atomic layers or smaller is 90% or more, it can be said that the interface Im, is basically flat excluding local spikes, defect, or the like. If the interface Im, is flat, the Rashba effect can be caused more effectively.

In addition, it is preferable that two layers with at least one interface of the interfaces included in the spin orbit torque wiring60interposed therebetween be epitaxially grown. In addition, it is preferable that all two layers with the interface included in the spin orbit torque wiring60interposed therebetween be epitaxially grown.

For example, whether or not the mth layer60mand the m+1th layer60m+1 are epitaxially grown can be confirmed by the fact that the atoms A are consecutively arrayed in an image of a transmission electron microscope (TEM). When the mth layer60mand the m+1th layer60m+1 are epitaxially grown, as shown inFIG.11, if an array of the atoms A is confirmed in order from the lower layer, it is possible to draw the line L in which the atoms A are arranged in a row. When these layers are not epitaxially grown, obvious distortion can be confirmed and the line L is disconnected in the middle of the way.

In addition, it is preferable that the lattice misfit rate in two layers with at least one interface of the interfaces included in the spin orbit torque wiring60interposed therebetween be lower than 5%. In addition, it is preferable that the lattice misfit rate in all two layers with the interface included in the spin orbit torque wiring60interposed therebetween be lower than 5%.

The lattice misfit rate in the interface Im, is obtained by (“Lattice constant a60m, of mth layer60m,”—“Lattice constant a60m+1of m+1th layer60m+1”)/“Lattice constant a60m, of mth layer60m,”. If the lattice misfit rate is within the foregoing range, crystallinity of each layer increases so that the flat interface Im, is obtained.

In addition, for example, the interface roughness of the interface may become higher as it is closer to the laminate10. If an interface far from the first ferromagnetic layer1is flat, even spins generated in the interface at a position away from the first ferromagnetic layer1can be injected into the first ferromagnetic layer1.

The magnetoresistive effect element110can be manufactured by a procedure similar to that of the magnetoresistive effect element100. When the interface roughness R of the interface between the layers is set within a predetermined range, every time each of the layers constituting the spin orbit torque wiring60is laminated, the surface thereof is subjected to chemical mechanical polishing or plasma treatment.

In the magnetoresistive effect element110according to the second embodiment, the combinations of the materials of the layers in the spin orbit torque wiring60are asymmetric in the z direction, and therefore it is possible to curb a situation in which spins generated due to the Rashba effect in the interfaces cancel each other out. For this reason, spins can be effectively injected into the first ferromagnetic layer1from the spin orbit torque wiring60, and a reversal current density can be reduced. In addition, since the paired interfaces have different areas, it is possible to further curb a situation in which spins generated in the respective interfaces cancel each other out.

InFIG.9, an example in which a plurality of interfaces included in the spin orbit torque wiring60differ from each other has been described, but there is no need for all the interfaces to have different areas. For example, only two interfaces (the first interface and the second interface) of a plurality of interfaces included in the spin orbit torque wiring60may have different areas. In addition, it is preferable that interfaces having different areas in a plurality of interfaces be two interfaces constituting paired interfaces.

First Modification Example

FIG.12is a cross-sectional view of a magnetoresistive effect element111according to a first modification example of the second embodiment. In the magnetoresistive effect element111, the same reference signs are applied to constituents similar those of the magnetoresistive effect element110, and description thereof will be omitted.

The magnetoresistive effect element111differs from the magnetoresistive effect element110in laminating order of the laminate10and the spin orbit torque wiring60. The spin orbit torque wiring60is laminated on the laminate10.

The laminate10has the base layer4, the second ferromagnetic layer2, the non-magnetic layer3, the first ferromagnetic layer1, and the cap layer5in this order from the side closer to the substrate Sub. In the magnetoresistive effect element111, the second ferromagnetic layer2(magnetization fixed layer) is closer to the substrate Sub than the first ferromagnetic layer1and is referred to as a bottom pin structure. The length of the first surface of the first ferromagnetic layer1on the spin orbit torque wiring60side in the x direction is shorter than the length of the second surface on a side opposite to the first surface in the x direction.

The spin orbit torque wiring60shown inFIG.12has four or more layers. For example, the spin orbit torque wiring60shown inFIG.12has the first layer601, the second layer602, and so on to n layers (n is an integer of 4 or larger), such as the nth layer60n, in this order from the side closer to the first surface60A. In addition, the spin orbit torque wiring60shown inFIG.12has the first interface I1, the second interface I2, and so on to the n−1th interface In−1in this order from the side closer to the first surface60A.

In the spin orbit torque wiring60, the combinations of the materials of the layers are asymmetric in the z direction. In the spin orbit torque wiring60, the sequence of material types in which the materials of the layers of the spin orbit torque wiring60are arranged from the first surface60A toward the second surface60B differs from the sequence of material types in which the materials of the layers of the spin orbit torque wiring60are arranged from the second surface60B toward the first surface60A. For example, the length of the first surface60A of the spin orbit torque wiring60in the x direction is longer than the length of the second surface60B of the spin orbit torque wiring60in the x direction. The paired interfaces in the spin orbit torque wiring60have different areas. The interfaces of the spin orbit torque wiring60may have different areas.

In addition, for example, the interface roughness of the interface may become lower as it is closer to the laminate10. If an interface close to the first ferromagnetic layer1is flat, more spins can be injected into the first ferromagnetic layer1from the interface.

In addition, inFIG.12, the first via wiring30and the second via wiring40are connected to the same surface as the surface of the spin orbit torque wiring60to which the laminate10is connected, but they may be connected to a different surface.

The magnetoresistive effect element111according to the first modification example of the second embodiment exhibits effects similar to those of the magnetoresistive effect element110.

Second Modification Example

FIG.13is a cross-sectional view of a magnetization rotation element112according to a second modification example of the second embodiment. The magnetization rotation element112differs from the magnetoresistive effect element110in that the second ferromagnetic layer2and the non-magnetic layer3are not provided. The magnetization rotation element112is an example of a magnetic element.

The magnetization rotation element112is similar to the magnetization rotation element102except that the spin orbit torque wiring60have four or more layers.

In the magnetization rotation element112according to the second modification example, the non-magnetic layer3and the second ferromagnetic layer2are simply removed from the magnetoresistive effect element110, and it is possible to achieve effects similar to those of the magnetoresistive effect element110.

Thus far, preferred aspects of the present invention have been described as examples by describing several embodiments as examples, but the present invention is not limited to these embodiments. For example, characteristic constitutions in each of the embodiments may also be applied to other embodiments and modification examples.

EXPLANATION OF REFERENCES