WO2020090719A1

WO2020090719A1 - Spin torque generating element, manufacturing method thereof, and magnetization control device

Info

Publication number: WO2020090719A1
Application number: PCT/JP2019/042137
Authority: WO
Inventors: 義近大谷; 俊延金; 浩太近藤
Original assignee: 国立研究開発法人理化学研究所
Priority date: 2018-10-31
Filing date: 2019-10-28
Publication date: 2020-05-07
Also published as: JPWO2020090719A1

Abstract

A spin torque generating element 10 comprises: a conductive layer 1 supplied with a current Jc; an insulating layer 2 formed on a surface on one side of the conductive layer 1; and a ferromagnetic layer 3 formed on a surface on the other side of the conductive layer 1. The current in the conductive layer 1 generates spin torque which acts on the magnetization of the ferromagnetic layer 3.

Description

Spin torque generating element, manufacturing method thereof, and magnetization control device

The present invention relates to a spin torque generating element that generates spin torque for magnetization of a ferromagnetic layer by a current flowing through a conductor layer. The present invention also relates to a method of manufacturing a spin torque generating element, and a magnetization control device including the spin torque generating element.

The spin torque generating element includes a conductor layer formed of a conductor such as a transition metal and a ferromagnetic layer formed of a ferromagnetic material. When a current flows through the conductor layer, the spin torque that acts on the magnetization of the ferromagnetic layer. Is an element that generates. The spin torque can change the magnetization direction of the ferromagnetic layer. For example, the direction of the magnetization can be reversed, or the precession motion of the magnetization can be self-oscillated. A magnetic memory, a microwave oscillator, a spin wave logic, and the like that utilize such a change in the direction of magnetization have been proposed.

For example, Patent Document 1 discloses an STT-MRAM (Spin-Transfer Torque Magnetic Random Access Memory) as a magnetic memory including a spin torque generating element. In this STT-MRAM, a conductor layer formed of a heavy metal, a recording layer (ferromagnetic layer) formed of a ferromagnetic material, a barrier layer formed of an insulating material, and a magnetization direction formed of a ferromagnetic material. The reference layers to which is fixed are laminated in this order. When an electric current is applied to the conductor layer while an external magnetic field is applied to the STT-MRAM in the stacking direction of the layers, a spin current is generated in the conductor layer due to the spin Hall effect, and the spin torque due to the spin current causes the recording layer to act. The magnetization direction of is reversed.

International Publication No. 2016/021468

According to the conventional spin torque generation principle in the spin torque generation element, as described above, when a current flows in the conductor layer, a spin current is generated by the spin Hall effect, and the spin torque due to the spin current acts on the magnetization of the ferromagnetic layer. There is.

In the past, in order to generate a spin current, it is believed that the conductor layer needs to be formed of a heavy metal that has a large spin-orbit coupling (SOC: Spin Orbit Coupling). For example, in Patent Document 1, the conductor layer is formed of Hf, W, Re, Os, Ir, Pt, Pb, or an alloy thereof which is a heavy metal. Such a heavy metal has a high electric resistance, and accordingly, the efficiency of passing a current through the conductor layer is reduced. As a result, the efficiency of causing a current to flow through the conductor layer to generate spin torque as described above becomes low. Further, heavy metal materials having a large specific gravity tend to be expensive and difficult to obtain.

Therefore, an object of the present invention is to provide a technique capable of generating a spin torque by the current of the conductor layer without using a conductor layer having a large specific gravity due to the configuration different from the conventional one.

The spin torque generating element according to the present invention includes a conductor layer to which a current is supplied, an insulating layer formed on one surface of the conductor layer, and a ferromagnetic layer formed on the other surface of the conductor layer. Equipped with
A spin torque that acts on the magnetization of the ferromagnetic layer is generated by the current in the conductor layer.

Further, the manufacturing method according to the present invention includes a conductor layer to which an electric current is supplied, an insulating layer formed on one surface of the conductor layer, and a ferromagnetic layer formed on the other surface of the conductor layer. A method for manufacturing a spin torque generating element, comprising: generating a spin torque that acts on the magnetization of the ferromagnetic layer by a current in the conductor layer,
A first step of forming the ferromagnetic layer, the conductor layer, and the insulating layer with respective materials so that the ferromagnetic layer, the conductor layer, and the insulating layer are laminated in this order;
A second step of performing an annealing treatment for heating the laminated ferromagnetic layer, the conductor layer, and the insulating layer.

Further, the magnetization control device according to the present invention is
A conductor layer to which a current is supplied, an insulating layer formed on one surface of the conductor layer, and a ferromagnetic layer formed on the other surface of the conductor layer are provided. A spin torque generating element that generates a spin torque that acts on the magnetization of the ferromagnetic layer,
A current supply device for supplying a current to the conductor layer,
The current supply device controls the direction of magnetization of the ferromagnetic layer by the spin torque by passing a current through the conductor layer.

The spin torque generating element of the present invention includes a conductor layer, an insulating layer formed on one surface of the conductor layer, and a ferromagnetic layer formed on the other surface of the conductor layer. A spin torque that acts on the magnetization of the ferromagnetic layer can be generated by passing an electric current through the layer. In such a configuration of the present invention, the conductor layer does not need to be formed of a heavy metal having a large spin-orbit interaction. Therefore, spin torque can be generated by the current of the conductor layer without using the conductor layer having a large specific gravity.

1 shows a configuration of a spin torque generating element according to an embodiment of the present invention. It is explanatory drawing of the spin torque generation principle in embodiment of this invention. The periodic table of elements for explaining the material of the conductor layer is shown. The measuring device which measures a spin torque is shown. It is explanatory drawing of the magnetic resonance utilized in the measurement of spin torque. About the Example of a spin torque generating element, the voltage measured value with a voltmeter and its symmetrical component and asymmetrical component are shown. The voltage measurement value by a voltmeter and its symmetrical component and asymmetrical component are shown about another Example of a spin torque generating element. The measurement result of the conversion efficiency with respect to the thickness of a conductor layer is shown. The other measurement result of the conversion efficiency with respect to the thickness of a conductor layer is shown. The measurement result of the conversion efficiency with respect to the material of the ferromagnetic layer is shown. The measurement result of the conversion efficiency with respect to the heating temperature of annealing treatment is shown. 6 is a flowchart showing a method of manufacturing a spin torque generating device according to an embodiment of the present invention. 1 shows a schematic configuration of a magnetization control device according to an embodiment of the present invention. It is explanatory drawing at the time of comprising a magnetization control apparatus as a spin logic device. The operation characteristic of the spin torque generation element which comprises a spin logic device is shown. The structural example of the magnetization control apparatus as a spin logic device is shown. It is a table which shows the output digital signal with respect to an input digital signal. An example of the configuration when the magnetization control device is a magnetic sensor is shown.

Embodiments of the present invention will be described with reference to the drawings. In addition, in each figure, the common part is denoted by the same reference numeral, and the duplicated description will be omitted.

(Outline of configuration of spin torque generating element)
FIG. 1 shows the configuration of a spin torque generating element 10 according to an embodiment of the present invention. The spin torque generating element 10 includes a conductor layer 1, an insulating layer 2 and a ferromagnetic layer 3. The conductor layer 1 is a layer to which an electric current is supplied. The conductor layer 1 may be formed of a metal material (for example, transition metal). The insulating layer 2 is formed of an insulating material on the surface of the conductor layer 1 on one side in the thickness direction. The ferromagnetic layer 3 is formed of a ferromagnetic material on the surface of the conductor layer 1 on the other side in the thickness direction.

According to the present invention, the conductor layer 1, the insulating layer 2, and the ferromagnetic layer 3 generate the spin torque that acts on the magnetization of the ferromagnetic layer 3 by the current of the conductor layer 1, respectively, the respective metal material and insulating material. , And a ferromagnetic material. According to the present embodiment, the conductor layer 1, the insulating layer 2, and the ferromagnetic layer 3 are made of a metal material, an insulating material, and a ferromagnetic material that cause a specific spin torque generation phenomenon described later in the spin torque generation element 10. Has been formed. That is, these metallic materials, insulating materials, and ferromagnetic materials are selected as a combination of materials that cause a specific spin torque generation phenomenon.

<Principle of spin torque generation phenomenon>
FIG. 2 is a diagram for explaining the principle of a specific spin torque generation phenomenon according to the embodiment of the present invention. The specific spin torque generation phenomenon in the spin torque generation element 10 occurs as follows. That is, as shown in FIG. 2, when a current Jc flows in the conductor layer 1, the orbital angular momentum (Orbital Angular Momentum) of each electron at the interface 4 between the conductor layer 1 and the insulating layer 2 due to the orbital Rashba effect. L is generated, and each orbital angular momentum L generates spin torque Ts that acts on the magnetization M of the ferromagnetic layer 3. Here, the current Jc flows from one end of the conductor layer 1 to the other end along the interface 4. The current Jc flows not only in the conductor layer 1 but also in the ferromagnetic layer 3.

The orbital Rashba effect is an effect in which, in the spin torque generating element 10, a current Jc flows in the conductor layer 1 in a direction along the interface 4, so that the orbital angular momentum of each electron is generated at the interface 4. Due to the action of the spin torque Ts due to the orbital angular momentum of each electron generated by this effect, the orbits of the electrons in the ferromagnetic layer 3 are combined (mixed), and as a result, the spin directions of the electrons in the ferromagnetic layer 3 change. The direction of the magnetization M of the ferromagnetic layer 3 changes. For example, the magnetization M of the ferromagnetic layer 3 is reversed.

(Detailed configuration of spin torque generating element)
In the principle of the specific spin torque generation phenomenon described above, unlike the conventional principle of the spin torque generation phenomenon, not the spin torque due to the spin current but the spin torque due to the orbital angular momentum of the electrons is generated. In order to generate spin torque due to the orbital angular momentum of electrons, the conductor layer 1 does not need to be formed of a heavy metal having a large spin orbital interaction. Therefore, in this embodiment, the conductor layer 1 is formed of a metal material having a small specific gravity as described below.

Therefore, according to the present embodiment, as long as the conductor layer 1 can cause the above-described specific spin torque generation phenomenon, as shown in FIG. 3, from the second period to the fifth period in the periodic table of elements. Is formed of a material of a metal element belonging to the range (that is, a metal element included in the range R1 in FIG. 3). In this case, the conductor layer 1 may be formed of the material of the transition metal included in the range R1 (that is, the metal element belonging to the range R2 in FIG. 3).

Alternatively, from another perspective, the conductor layer 1 may be formed of a material having a specific gravity of 10 or less, for example. Here, the specific gravity means the ratio of the standard substance having the same volume (that is, water at 4 ° C.) to the mass.

The conductor layer 1 is made of copper (Cu) in the embodiment. Here, the copper may be pure copper or a copper alloy. The main component of the copper alloy is Cu, and the remaining material of the copper alloy may be a material of a metal element included in the range R1 (or the range R2) of the periodic table. The conductor layer 1 may have a thickness of several nm (for example, 4 nm or 5 nm) or more and several tens nm (for example, 20 nm or 30 nm) or less.

The insulating layer 2 is an electrical insulator and forms an interface 4 with the conductor layer 1. The insulating layer 2 is a layer for generating the orbital angular momentum of each electron by the above-described orbital Rashba effect at the interface 4. In the embodiment, the insulating material forming the insulating layer 2 is aluminum oxide (Al ₂ O ₃ ) or magnesium oxide (MgO).

The ferromagnetic layer 3 is a ferromagnetic material and is magnetized in the direction along the interface 4. The magnetization M of the ferromagnetic layer 3 changes its direction (for example, reverses) under the action of the above-mentioned spin torque Ls generated by the above-mentioned orbital Rashba effect. The ferromagnetic layer 3 is formed of a ferromagnetic material that causes such a change in the direction of the magnetization M. The ferromagnetic material forming the ferromagnetic layer is iron (Fe) or cobalt iron (CoFe) in the examples.

As described above, in the example of this embodiment, the conductor layer 1 is made of copper, the insulating layer 2 is made of aluminum oxide or magnesium oxide, and the ferromagnetic layer 3 is made of iron or cobalt iron. However, the present embodiment is not limited to this, and the metal material, the insulating material, and the ferromagnetic material that form the conductor layer 1, the insulating layer 2, and the ferromagnetic layer 3, respectively, are the same as those described above. It may be selected as a combination of materials that cause the torque generation phenomenon. In this case, the metal material of the conductor layer 1 may be limited to the metal element material included in the range R1 of FIG. The selection of such metal material, insulating material, and ferromagnetic material may be performed by confirming whether or not the spin torque Ts is generated by the measuring device 20 described later. For example, the metal material, the insulating material, and the ferromagnetic material that form the conductor layer 1, the insulating layer 2, and the ferromagnetic layer 3, respectively, have a conversion efficiency θ described below of 0.05 or more, 0.1 or more, or 0.2. It may be selected as a combination of the above materials.

(Experiment for Examples)
FIG. 4 shows a measuring device 20 for measuring the spin torque Ts. Using this measuring device 20, the spin torque Ts or the like generated in the spin torque generating element 10 was measured as follows.

The measuring device 20 is a device that uses the spin torque magnetic resonance method, and includes a pair of

electrodes

5a and 5b, a capacitor 6, an AC power supply 7, a coil 8, and a voltmeter 9. The pair of

electrodes

5a and 5b are in contact with both ends of the spin torque generating element 10, respectively. One electrode 5a is connected to an AC power supply 7 via a capacitor 6, and the other electrode 5b is grounded. The voltmeter 9 is connected to the current path between the one electrode 5a and the capacitor 6 via the coil 8. With this configuration, the voltmeter 9 measures the DC component (DC voltage) of the voltage generated at the one electrode 5a.

Further, in FIG. 4, in the coordinate system having the x-axis, the y-axis, and the z-axis which are orthogonal to each other, the x-axis and the y-axis are parallel to the interface 4 between the conductor layer 1 and the insulating layer 2. The AC power supply 7 applies a high frequency current to the conductor layer 1 (and the ferromagnetic layer 3) in the x-axis direction. Further, the external magnetic field H _ext is applied by means not shown. The direction of the external magnetic field H _{ext is} a direction orthogonal to the z axis and forms an acute angle φ with the x axis. The external magnetic field H _ext and the current in the conductor layer 1 excite magnetic resonance, which is a precession of the magnetization M of the ferromagnetic layer 3.

FIG. 5 is an explanatory diagram of magnetic resonance. In FIG. 5, a coordinate system having an X axis, a Y axis, and a Z axis that are orthogonal to each other is fixed to the ferromagnetic layer 3, and these X axis, Y axis, and Z axis are respectively the x axis of FIG. It is parallel to the axes, the y-axis, and the z-axis. When a high frequency current is applied to the conductor layer 1 in the x-axis direction, the torque T _F due to the magnetic field generated by the current itself acts on the magnetization M of the ferromagnetic layer 3 in the direction parallel to the Z axis, as shown in FIG. To do. Further, the spin torque Ts described above caused by the current acts on the magnetization M in a direction parallel to the XY plane so as to tilt the magnetization M as shown in FIG. As a result, the magnetization M performs precession about an axis that points in the direction of the external magnetic field H _ext .

<Measurement result of voltage showing magnitude of spin torque>
6 and 7 show the DC voltage measured by the voltmeter 9 of the measuring device 20 of FIG. 4, and its symmetric and asymmetric components. The results of FIGS. 6 and 7 are obtained for the spin torque generating element 10 having the following specific configuration. That is, in the example of the spin torque generating element 10 in which the result of FIG. 6 is obtained, the conductor layer 1 is made of Cu, the insulating layer 2 is made of Al ₂ O ₃ , and the ferromagnetic layer 3 is made of CoFe. The thicknesses of the conductor layer 1, the insulating layer 2 and the ferromagnetic layer 3 are 6.9 nm, 20 nm and 5 nm, respectively. In the embodiment of the spin torque generating element 10 in which the result of FIG. 7 is obtained, the conductor layer 1 is formed of Cu, the insulating layer 2 is formed of MgO, the ferromagnetic layer 3 is formed of CoFe, and the conductor layer 1 is formed. The thicknesses of the insulating layer 2 and the ferromagnetic layer 3 are 10.9 nm, 20 nm and 5 nm, respectively.

6 and 7, the horizontal axis represents the strength of the applied external magnetic field H _ext , and the vertical axis represents the voltage. In FIG. 6 and FIG. 7, each square mark indicates the measured value of the DC voltage measured by the voltmeter 9, the solid line curve is the fitting curve of each measured value, and the broken line curve is the symmetric component of the fitting curve. And the dashed-dotted curve represents the asymmetric component of the Fitting curve. Here, the symmetric component corresponds to the contribution of spin torque, and the asymmetric component corresponds to the contribution of torque due to the magnetic field generated by the current itself flowing through the conductor layer 1.

Note that the symmetric component and the asymmetric component were obtained according to the calculation formula assuming that the spin torque due to the spin current generated by the current acts on the magnetization of the ferromagnetic layer 3. However, it is unlikely that the spin torque due to the spin current is generated in the copper having a small specific gravity. Therefore, it can be said that the symmetric component and the asymmetric component are values due to the spin torque due to the orbital angular momentum of the electrons generated at the interface 4.

6 and 7, it can be seen that a peak occurs in the symmetrical component, and a spin torque having a magnitude corresponding to the magnitude of the peak is generated. As described above, it was confirmed that the spin torque generating element 10 generates spin torque when a current flows through the conductor layer 1.

In FIG. 7, the symmetric component having a sharp peak has a considerably large (that is, fairly efficient) spin due to the combination of the materials of the conductor layer 1, the insulating layer 2, and the ferromagnetic layer 3 being Cu, MgO, and CoFe. It shows that torque is generated.

<Measurement result of conversion efficiency with respect to thickness of conductor layer>
8 and 9 show the measurement results of the conversion efficiency θ with respect to the thickness of the conductor layer 1 obtained using the measuring device 20 of FIG. 4. 8 and 9, the horizontal axis represents the thickness of the conductor layer 1 made of copper, and the vertical axis represents the conversion efficiency θ from the current of the conductor layer 1 to the spin torque.

Θ is represented by Js / Jc, Jc is the value of the current flowing through the conductor layer 1, and Js is the value of the current corresponding to the spin torque. Here, Js represents the value of the spin current on the assumption that the spin torque generated by the spin current generated by the current Jc acts on the magnetization M of the ferromagnetic layer 3. However, as described above, it is unlikely that the spin torque due to the spin current is generated in copper having a small specific gravity, and thus Js is a current corresponding to the spin torque due to the orbital angular momentum of the electrons generated at the interface 4. Can be said.

Further, in FIG. 8, a square plot indicates a spin torque generation element 10 in which the conductor layer 1 is made of Cu, the insulating layer 2 is made of Al ₂ O ₃ , and the ferromagnetic layer 3 is made of CoFe. The circled plots show the case of the spin torque generation element 10 in which the conductor layer 1 is formed of Cu, the insulating layer 2 is formed of Bi ₂ O ₃ , and the ferromagnetic layer 3 is formed of CoFe.

In FIG. 9, the circled plots show the case of the spin torque generating element 10 in which the conductor layer 1 is made of Cu, the insulating layer 2 is made of MgO, and the ferromagnetic layer 3 is made of CoFe.

As can be seen from FIG. 8, when the insulating layer 2 is Al ₂ O ₃ , the conversion efficiency θ is significantly improved as compared with the case where the insulating layer 2 is Bi ₂ O ₃ . For example, the peak value of the conversion efficiency θ when the insulating layer 2 is Al ₂ O ₃ is _twice the peak value of the conversion efficiency θ when the insulating layer 2 is Bi ₂ O _3. Is also getting bigger. Therefore, it can be seen that a large conversion efficiency θ can be obtained when the insulating layer 2 is Al ₂ O ₃ .

Further, as can be seen from FIGS. 8 and 9, the peak value of the conversion efficiency θ when the insulating layer 2 is MgO is the peak value of the conversion efficiency θ when the insulating layer 2 is Al ₂ O _3. It is less than twice the size of. Therefore, it can be seen that when the insulating layer 2 is MgO, the conversion efficiency θ is further improved as compared with the case where the insulating layer 2 is Al ₂ O ₃ .

Further, as shown in FIGS. 8 and 9, when the insulating layer 2 is Al ₂ O ₃ or MgO, the conversion efficiency θ depends on the thickness of the conductor layer 1. Therefore, it is understood that the conversion of the current J _C into the spin torque is caused by the existence of the conductor layer 1 and the interface 4.

An example of the numerical range of the thickness of the conductor layer 1 when the conductor layer 1 is formed of Cu, the insulating layer 2 is formed of Al ₂ O ₃ and the ferromagnetic layer 3 is formed of CoFe will be described. The conductor layer 1 may have a thickness of 5 nm or more and 19 nm or less. In this case, in FIG. 8, the conversion efficiency θ regarding the plot of the square mark becomes a value of slightly less than 0.05. Moreover, the thickness of the conductor layer 1 may be a value within the range of 7 nm or more and 15 nm or less. In this case, in FIG. 8, the conversion efficiency θ regarding the plot of the square mark is a value of about 0.10. Further, the thickness of the conductor layer 1 may be a value in the range of 9 nm or more and 13 nm or less. In this case, in FIG. 8, the conversion efficiency θ regarding the plot of the square mark is a value near its maximum value (a little less than 0.13).

An example of the numerical range of the thickness of the conductor layer 1 when the conductor layer 1 is formed of Cu, the insulating layer 2 is formed of MgO, and the ferromagnetic layer 3 is formed of CoFe will be described. The conductor layer 1 may have a thickness of 4.5 nm or more and 27 nm or less. In this case, in FIG. 9, it can be said that the conversion efficiency θ regarding the plot of the square mark becomes a value of 0.05 or more. Further, the thickness of the conductor layer 1 may be a value in the range of 6 nm or more and 26 nm or less. In this case, in FIG. 9, the conversion efficiency θ regarding the plot of the square mark is a value larger than 0.10. Moreover, the thickness of the conductor layer 1 may be a value within the range of 9 nm or more and 17 nm or less. In this case, in FIG. 9, the conversion efficiency θ regarding the plot of the square mark is a value near its maximum value (a little less than 0.25).

<Measurement result of conversion efficiency for material of ferromagnetic layer>
FIG. 10 shows the measurement results of the conversion efficiency θ with respect to the material of the ferromagnetic layer 3 obtained using the measuring device 20 of FIG. That is, in FIG. 10, in the spin torque generating element 10, the conductor layer 1 is made of Cu and the insulating layer 2 is made of Al ₂ O ₃ , but the measurement is made for each case in which the material of the ferromagnetic layer 3 is changed. The results are shown. In FIG. 10, the horizontal axis represents the saturation magnetization of the ferromagnetic layer 3, and the vertical axis represents the conversion efficiency θ from the current of the conductor layer 1 to the spin torque. In FIG. 10, each black circle indicates a measured value when the ferromagnetic layer 3 is formed of the material indicated by the arrow indicating the black circle.

As shown in FIG. 10, the highest conversion efficiency θ (less than 0.13) was obtained when the ferromagnetic layer 3 was formed of CoFe. Further, when the ferromagnetic layer 3 was formed of Fe, the next highest conversion efficiency θ (about 0.1) was obtained. When the ferromagnetic layer 3 was Ni (nickel) or Py (permalloy), the conversion efficiency θ became zero or almost zero.

As described above, it is understood that the orbital Rashba effect (specific spin torque generation phenomenon) can be obtained when the materials forming the conductor layer 1, the insulating layer 2, and the ferromagnetic layer 3 are specific combinations. In the examples of FIGS. 6 to 10, when the combination is Cu and Al ₂ O ₃ and CoFe, Cu and Al ₂ O ₃ and Fe, or Cu and MgO and CoFe, the above-mentioned orbital Rashba effect is obtained. It was confirmed. However, according to the present embodiment, if the orbital Rashba effect is obtained, the combination of materials forming the conductor layer 1, the insulating layer 2, and the ferromagnetic layer 3 may be another combination (for example, Cu, MgO, and Fe, respectively). It may be.

When the conductor layer 1 is made of Cu and the insulating layer 2 is made of Al ₂ O ₃ or MgO, the ferromagnetic material forming the ferromagnetic layer 3 is not limited to CoFe or Fe. In the example shown in FIG. 10, the saturation magnetization of Fe as the ferromagnetic material is about 10 kOe or more, and the saturation magnetization of CoFe as the ferromagnetic material is about 13 kOe or more. The upper limit of the saturation magnetization of the ferromagnetic material is not particularly limited, but the saturation magnetization may be, for example, 20 kOe or less. In the present application, the saturation magnetization of the ferromagnetic material is the ferromagnetic material (that is, the ferromagnetic layer 3) in a state of constituting the spin torque generating element 10 (before or after the annealing treatment described later) after manufacturing. ) Saturation magnetization, and may be a value at room temperature.

<Results of measurement of conversion efficiency for annealing treatment>
FIG. 11 shows the measurement result of the conversion efficiency θ with respect to the heating temperature of the annealing treatment, which is obtained using the measuring device 20 of FIG. FIG. 11 shows the case where the conductor layer 1 is made of Cu, the insulating layer 2 is made of Al ₂ O ₃ , and the ferromagnetic layer 3 is made of CoFe. However, when the annealing treatment is performed at each heating temperature. The measured value of 1 and the measured value when the annealing treatment is not performed are shown. In FIG. 11, the horizontal axis represents the saturation magnetization of the ferromagnetic layer 3, and the vertical axis represents the conversion efficiency θ from the current of the conductor layer 1 to the spin torque.

Further, in FIG. 11, each black circle shows a measured value when the conductor layer 1, the insulating layer 2, and the ferromagnetic layer 3 were laminated by vapor deposition at a temperature indicated by an arrow indicating the black circle, and then heated for 30 minutes. Here, the temperature is the temperature of the conductor layer 1, the insulating layer 2, and the ferromagnetic layer 3. Further, in FIG. 11, the black circles indicated by the arrows with “NO ANNEALING” indicate the measured values when the annealing treatment was not performed.

As shown in FIG. 11, it can be seen that the conversion efficiency θ is significantly improved by performing the annealing treatment. For example, by performing the annealing treatment at 400 ° C., the conversion efficiency θ was more than doubled and became close to 0.3. In this way, the annealing treatment makes it possible to maximize the conversion efficiency θ.

In the spin torque generating element 10 according to each example, since the resistivity of the conductor layer 1 is significantly smaller than the resistivity of heavy metals such as tungsten (W), the spin torque generating efficiency is correspondingly increased as follows. It can be said to be expensive. As described above, the conversion efficiency θ obtained by the annealing treatment at 400 ° C. is the same value as the case where tungsten is used for the conductor layer in the above-described conventional spin torque generating element. Since the resistivity of thin film tungsten having a nanoscale thickness is approximately 12 times or more the resistivity of thin film copper having a nanoscale thickness, the conductor layer 1 of the spin torque generating element 10 according to each example is The electric resistance of is small by that amount. As a result, in each of the examples, it can be said that the spin torque generation efficiency is improved 12 times or more as compared with the conventional case.

Therefore, when the conductor layer 1, the insulating layer 2, and the ferromagnetic layer 3 are formed of Cu and Al ₂ O ₃ or MgO and CoFe, respectively, or when the conductor layer 1, the insulating layer 2, and the ferromagnetic layer 3 are formed, respectively. When the materials used are other combinations, annealing treatment can be performed in order to improve the conversion efficiency θ. In this case, the annealing treatment may heat the conductor layer 1, the insulating layer 2, and the ferromagnetic layer 3 which are laminated on each other at a temperature of 200 ° C. or higher, 300 ° C. or higher, or 400 ° C. or higher. That is, the annealing treatment may be performed so that the temperatures of the conductor layer 1, the insulating layer 2, and the ferromagnetic layer 3 are 200 ° C. or higher, 300 ° C. or higher, or 400 ° C. or higher. 6 to 10 show the results when the annealing process was not performed.

(Method of manufacturing spin torque generating element)
FIG. 12 is a flowchart showing a method of manufacturing the spin torque generating element 10 according to the embodiment of the present invention. This manufacturing method includes steps S1 and S2.

In step S1, the ferromagnetic layer 3, the conductor layer 1 and the insulating layer 2 are formed of respective materials so that the ferromagnetic layer 3, the conductor layer 1 and the insulating layer 2 are laminated in this order. This stacking may be performed by a vapor deposition method. For example, the ferromagnetic layer 3 is formed by adhering the heated and evaporated ferromagnetic material to the surface of the substrate. Next, the insulating layer 2 is formed by adhering the heated and evaporated insulating material to the surface of the ferromagnetic layer 3. After that, the conductor layer 1 is formed by adhering the heated and evaporated metal material to the surface of the insulating layer 2. Thereby, a laminated body including the ferromagnetic layer 3, the conductor layer 1, and the insulating layer 2 is obtained. However, the formation and lamination of the ferromagnetic layer 3, the conductor layer 1, and the insulating layer 2 may be performed by other methods.

In step S1, in the embodiment, the ferromagnetic layer 3, the conductor layer 1, and the insulating layer 2 are formed of CoFe (or Fe) and Cu and Al ₂ O ₃ , or CoFe (or Fe) and Cu and MgO, respectively. However, it may be formed of other materials.

In step S2, annealing treatment for heating the conductor layer 1, the insulating layer 2, and the ferromagnetic layer 3 laminated in step S1 is performed (for example, 30 minutes). In this annealing treatment, the temperature for heating the conductor layer 1, the insulating layer 2, and the ferromagnetic layer 3 is 200 ° C. or higher, 300 ° C. or higher, or 400 ° C. or higher. That is, the annealing treatment is performed so that the temperatures of the conductor layer 1, the insulating layer 2, and the ferromagnetic layer 3 are 200 ° C. or higher, 300 ° C. or higher, or 400 ° C. or higher.

(Effects of the embodiment)
According to the spin torque generation element 10 of the above-described embodiment, by passing a current through the conductor layer 1, the orbital angular momentum of each electron generated at the interface 4 between the conductor layer 1 and the insulating layer 2 due to the orbital Rashba effect becomes strong. A spin torque that acts on the magnetization of the magnetic layer 3 is generated. According to such a principle of spin torque generation, the conductor layer 1 does not need to be formed of a heavy metal having a large spin-orbit interaction. Therefore, spin torque can be generated by the current of the conductor layer 1 without using the conductor layer 1 having a large specific gravity.
In the spin torque generating element 10 and the manufacturing method thereof according to the above-described embodiment, the conductor layer 1 is formed of a metal material having a relatively small specific gravity (for example, a metal element material within the range R1 or R2 of the periodic table of FIG. 3). It The metal material (for example, copper) tends to be easily available. Therefore, the spin torque generating element 10 can be mass-produced at low cost.

Further, since such a metal material has a relatively small specific gravity, the conductor layer 1 formed of the metal material has a low electric resistivity. Therefore, the generation efficiency of the spin torque Ts is correspondingly improved. Furthermore, by performing the above-described annealing treatment, the conversion efficiency from the current of the conductor layer 1 to the spin torque Ts is improved.

Therefore, it becomes possible to mass-produce the spin torque generating element 10 having extremely high conversion efficiency at low cost.

(Magnetization control device)
FIG. 13 shows a schematic configuration of the magnetization control device 100 according to the embodiment of the present invention. The magnetization control device 100 includes the above-described spin torque generating element 10 and a current supply device 11 that causes a current to flow in the conductor layer 1. The current supply device 11 applies a current to the conductor layer 1 in a direction along the interface 4 from one end of the spin torque generating element 10 to the other end, or from the other end of the spin torque generating element 10 to one end. A current is caused to flow in the conductor layer 1 in the direction toward, and the direction of the magnetization M of the ferromagnetic layer 3 is controlled by the above-described spin torque Ts generated thereby. For example, the spin torque Ts reverses the direction of the magnetization M or causes the magnetization M to precess. Here, in the latter case, in order to cause precession, the magnetization control device 100 applies a magnetic field application unit (for example, a permanent magnet or an electromagnet) 12 that applies an external magnetic field H _{ext in a} direction that is the central axis of the precession. May be provided.

<Application example to magnetic memory>
The magnetization control device 100 may form a magnetic memory. In this case, as shown in FIG. 13, the spin torque generating element 10 further includes a reference layer 13. In this case, the magnetic field applying unit 12 described above may be omitted. The reference layer 13 is formed of a ferromagnetic material, and is formed on the surface of the insulating layer 2 opposite to the conductor layer 1. The ferromagnetic material forming the reference layer 13 is, for example, Co, Fe, Ni or an alloy thereof, but is not limited thereto. The direction of the magnetization of the reference layer 13 (hereinafter simply referred to as the magnetization Mr) is fixed.

The current supply device 11 causes a current to flow along the interface 4 to the conductor layer 1 in the same direction as the direction of the magnetization Mr or in the direction opposite to the direction of the magnetization Mr, so that the orbits of electrons due to the above-described orbital Rashba effect at the interface 4. An angular momentum is generated, and the direction of the magnetization M of the ferromagnetic layer 3 is reversed by the spin torque Ts due to the orbital angular momentum. As a result, the direction of the magnetization M of the ferromagnetic layer 3 is made the same as the magnetization Mr or opposite to the magnetization Mr.

The magnetization control device 100 has a configuration in which a large number of such spin torque generating elements 10 are arranged. The current supply device 11 controls the direction of the magnetization M of the ferromagnetic layer 3 in each spin torque generating element 10 according to the write command. That is, the current supply device 11 causes a current to flow through the conductor layer 1 of each of the one or more spin torque generation elements 10 in accordance with the write command as described above, and the magnetization M of the ferromagnetic layer 3 of the element 10 concerned. Reverse the direction of. 1-bit data of “0” and “1” is assigned to two directions of the magnetization M of the ferromagnetic layer 3 in each element 10, and the data is stored in many elements 10.

In each spin torque generating element 10, the electric resistance between the reference layer 13 and the ferromagnetic layer 3 differs depending on the direction of the magnetization M of the ferromagnetic layer 3. Therefore, in each spin torque generation element 10, a read current is caused to flow between an electrode (not shown) provided in the reference layer 13 and an electrode (not shown) provided in the ferromagnetic layer 3, and the read current From the value, the electric resistance value between the reference layer 13 and the ferromagnetic layer 3 is detected, and the direction of the magnetization M of the ferromagnetic layer 3 is obtained as recording data based on the detected value.

<Application example to microwave oscillator>
The magnetization control device 100 shown in FIG. 13 may form a microwave oscillation device. In this case, the current supply device 11 supplies a current to the conductor layer 1 so that the direction of the magnetization M of the ferromagnetic layer 3 changes, and the microwave is generated by the change of the direction of the magnetization M.

For example, the current supply device 11 causes an alternating current to flow in the conductor layer 1 in one direction along the interface 4 (for example, in the left-right direction in FIG. 13) to repeatedly invert the direction of the magnetization M of the ferromagnetic layer 3 to cause a microscopic change. Generate waves. In this case, the reference layer 13 and the magnetic field applying unit 12 may be omitted.

Alternatively, the current supply device 11 causes a current to flow in the conductor layer 1 in the direction along the interface 4 (for example, the left-right direction in FIG. 13), and the magnetic field applying unit 12 applies the external magnetic field H _ext to the ferromagnetic layer 3 to the interface 4. The voltage is applied along the direction (for example, the direction forming an acute angle with the direction of the current of the conductor layer 1). As a result, as described above with reference to FIG. 4, the magnetization M is precessed with the direction of the external magnetic field H _ext as the central axis. As a result, microwaves are generated.

<Application to logic device>
FIG. 14 is an explanatory diagram when the above-described magnetization control device 100 is configured as a spin logic device. In this case, the magnetization control device 100 further includes a voltage applying device 14 that applies a gate voltage between the conductor layer 1 and the insulating layer 2, and a voltage that measures the voltage between the ferromagnetic layer 3 and the reference layer 13. It has a total of 15. The magnetic field applying unit 12 described above is omitted. The voltage value measured by the voltmeter 15 represents the direction of the magnetization M of the ferromagnetic layer 3.

FIG. 15 is a graph showing the operating characteristics of the spin torque generating element 10 that constitutes the spin logic device. In FIG. 15, the horizontal axis represents the value of the current supplied to the conductor layer 1 by the current supply device 11, and the positive / negative of the current value represents the direction of the current (rightward or leftward in FIG. 14). In FIG. 15, the vertical axis represents the voltage value measured by the voltmeter 15. On the vertical axis of FIG. 15, the measured voltage value being 1.0 (arb.) Is one of the two directions in which the magnetizations of the ferromagnetic layers 3 are opposite to each other (for example, the right direction in FIG. 14). That the measured voltage value is −1.0 (arb.) Means that it is the other of the above two directions (for example, the left direction in FIG. 14). Note that "arb." Indicates an arbitrary unit (the same applies hereinafter).

In FIG. 15, the thick dash-dotted line shows the operating characteristics when the above-mentioned gate voltage value is + V _G , and the thick solid line shows the operating characteristics when the above-mentioned gate voltage value is −V _G. Show. The switching of the magnetization direction of the ferromagnetic layer 3 is performed according to the thick solid line in FIG. 15, but is not performed according to the thick dash-dotted line in FIG. 15 (that is, when the absolute value is 6 (arb.) Or less). The current supply device 11 causes a current to flow in the conductor layer 1 by a large amount (less than 7 (arb.)).

FIG. 16 shows a configuration example of the magnetization control device 100 as a spin logic device. In FIG. 16, the magnetization control device 100 includes two sets of spin torque generation elements 10 (hereinafter also referred to as a set A and a set B) that share one conductor layer 1. That is, two sets of the insulating layer 2, the ferromagnetic layer 3 and the reference layer 13 are provided so as to share one conductor layer 1. Each set A, B has the operating characteristics shown in FIG.

The above-described voltage application device 14 and voltmeter 15 are provided for each set A and B. The voltage applying device 14 and the voltmeter 15 of the one set A are referred to as the voltage applying device 14A and the voltmeter 15A, respectively, and the voltage applying device 14 and the voltmeter 15 of the other set B are respectively the voltage applying device 14B and the voltmeter 15B. Enter.

Regarding the above gate voltage, + V _G is an input digital signal of “1” and −V _G is an input digital signal of “0”. The voltage applying device 14A changes the gate voltage applied to the set A while the current supply device 11 applies the current of the above-mentioned intermediate value (for example, −6.5 (arb.)) To the conductor layer 1. , + V _G and −V _G (that is, “1” and “0” of the digital signal), and the voltage application device 14B applies the gate voltage applied to the set B to + V _G and −V _G. When switching between and, the output digital signals for the two input digital signals are as shown in the table of FIG. In FIG. 17, “1” and “0” of the gate voltages to the sets A and B mean + V _G and −V _G , respectively, and V _T (arb.) Is the voltage measured by the

voltmeters

15A and 15B. It means the sum of the values V _T (arb.).

The magnetization control device 100 further includes an output unit 16 that outputs an output digital signal corresponding to the two input digital signals described above. When the output unit 16 is configured as a logical sum (OR), the measured voltage value of the voltmeter 15A and the measured voltage value of the voltmeter 15B are both 0 as in the case of the logical sum of FIG. If it is (arb.), A digital signal of "0" is output, and in other cases, a digital signal of "1" is output. On the other hand, when the output unit 16 is configured as a logical product (AND), the measured voltage value of the voltmeter 15A and the measured voltage value of the voltmeter 15B are determined as in the case of the logical product of FIG. Is also 1 (arb.), A digital signal of "1" is output, and in other cases, a digital signal of "0" is output.

The output unit 16 may be configured as follows, for example, to output a digital signal as shown in FIG. The current supply device 11 supplies a current whose absolute value is fixed to the intermediate value and whose sign is fixed to the negative value to the conductor layer 1. Due to the current in the conductor layer 1, the magnetization reversal of the ferromagnetic layer 3 of each set A, B is induced, and the total V _T (arb.) Of the voltage measurement values from the

voltmeters

15A, 15B becomes the respective magnetizations. It changes from -2 (arb.) To 2 (arb.) Depending on the state and the above-mentioned gate voltage as shown in FIG. When the logical sum is defined as the reference voltage _{1 (arb.), V T} (arb.) When is greater than the reference voltage, the output unit 16 outputs a digital signal _"0", V T (arb .) Is smaller than the reference voltage, the output unit 16 outputs the digital signal “1”. Similarly, in the case of logical product, the reference voltage is defined as -1 (arb.), And when V _T (arb.) Is larger than the reference voltage, the output unit 16 outputs a digital signal "0", When the total V _T (arb.) Is smaller than the reference voltage, the output unit 16 outputs the digital signal “1”. It should be noted that reference is made so that the total V _T (arb.) According to FIG. 17 is obtained for the above-mentioned gate voltage in the state where a negative current whose absolute value is the intermediate value is flowing in the conductor layer 1. The magnetization direction of the layer 13 is set.

<Application to magnetic sensor>
FIG. 18 shows a configuration example when the above-described magnetization control device 100 is used as a magnetic sensor. In the example of FIG. 18, the magnetization control device 100 includes first to fourth spin torque generation elements 10A to 10D. Each of these spin torque generating elements 10A to 10D may have the same configuration as the spin torque generating element 10 described above, and may be formed on the substrate 17. The substrate 17 may be formed of SiO ₂ , for example. The reference layer 13 and the magnetic field applying unit 12 may be omitted.

In FIG. 18, the xyz coordinate system is a coordinate system fixed with respect to the substrate 17, and its x-axis and y-axis are parallel to the surface (interface 4) of the substrate 17 and are orthogonal to each other. Are orthogonal to the surface (interface 4) of the substrate 17. Each of the spin torque generating elements 10A to 10D may have an elliptical shape when viewed in the thickness direction (z-axis direction) as a whole. The major axis of the ellipse may be oriented in the x-axis direction.

One ends of the conductor layers 1 of the first and second spin

torque generating elements

10A and 10B in the x-axis direction are connected to each other by a conductive line 18a, and the third and fourth spin

torque generating elements

10C and 10D. The one ends of the conductor layer 1 in the x-axis direction are also connected to each other by the conductive line 18b. The other ends of the conductor layers 1 of the first and third

spin torque elements

10A and 10C in the x-axis direction are connected to each other by a conductive line 18c, and the second and fourth

spin torque elements

10B and 10D are connected to each other. The other ends of the conductor layer 1 in the x-axis direction are also connected to each other by the conductive line 18d.

The current supply device 11 applies an alternating current between the conductive line 18a and the conductive line 18b. As a result, an alternating current flows in the x-axis direction in the conductor layer 1 of each of the spin torque generating elements 10A to 10D. The direction of magnetization of the ferromagnetic layer 3 in each of the spin torque generating elements 10A to 10D changes according to the alternating current.

The magnetization control device 100 further includes a voltmeter 18. The voltmeter 18 measures the voltage (potential difference) between the conductive line 18c and the conductive line 18d, and outputs the measured voltage value. This voltage value may be a time average value of the voltage measured by the voltmeter 18.

When an external magnetic field Hy in the y-axis direction is present in the magnetic sensor while the current supply device 11 is applying an alternating current between the conductive line 18a and the conductive line 18b, the voltage measured by the voltmeter 18 is the external voltage. It has a value corresponding to the magnetic field Hy. Therefore, the external magnetic field Hy can be detected based on the voltage value output by the voltmeter 18.

In one example, since the magnetic sensor by the magnetization control device 100 is very sensitive to the external magnetic field Hy, the attitude of the magnetic sensor (substrate 17) with respect to the ground changes, and the geomagnetic component in the y-axis direction also changes. Therefore, this change can be detected based on the output voltage value of the voltmeter 18. Therefore, since the attitude of the magnetic sensor can be detected, the attitude of the object to which the magnetic sensor is attached can also be detected.

The present invention is not limited to the above-mentioned embodiments, and it goes without saying that various modifications can be made within the scope of the technical idea of the present invention. For example, the spin torque generating element 10, the manufacturing method thereof, and the magnetization control device 100 may not have all of the plurality of items described above, and may have only a part of the plurality of items described above. Good. Further, the spin torque generating element 10, the method of manufacturing the same, and the magnetization control device 100 may not exhibit all of the above-described operational effects, and may exhibit only some of the above-described operational effects.

1 conductor layer, 2 insulating layer, 3 ferromagnetic layer, 4 interface, 5a, 5b electrode, 6 capacitor, 7 AC power supply, 8 coil, 9 voltmeter, 10 spin torque generating element, 11 current supply device, 12 magnetic field applying section , 13, reference layer, 14, 14A, 14B voltage applying device, 15, 15A, 15B voltmeter, 16 output section, 17 substrate, 18 voltmeter, 20 measuring device, 100 magnetization control device

Claims

A conductor layer to which an electric current is supplied; an insulating layer formed on one surface of the conductor layer; and a ferromagnetic layer formed on the other surface of the conductor layer,
A spin torque acting on the magnetization of the ferromagnetic layer is generated by the current of the conductor layer,
Spin torque generating element.
The conductor layer, the insulating layer, and the ferromagnetic layer are formed of respective materials that cause a specific spin torque generation phenomenon in the spin torque generation element,
In the specific spin torque generation phenomenon, when a current flows in the conductor layer, an orbital angular momentum of electrons occurs at the interface between the conductor layer and the insulating layer due to an orbital Rashba effect, and the orbital angular momentum causes The spin torque generating element according to claim 1, which is a phenomenon that generates a spin torque that acts on the magnetization of the layer.
The spin torque generation element according to claim 1 or 2, wherein the conductor layer is made of a material of a metal element belonging to a range from a second period to a fifth period in the periodic table of elements.
The spin torque generating element according to claim 3, wherein the conductor layer is made of copper.
The spin torque generating element according to claim 1, wherein the conductor layer is made of copper, the insulating layer is made of aluminum oxide or magnesium oxide, and the ferromagnetic layer is made of iron or cobalt iron.
The conductor layer is formed of copper, the insulating layer is formed of aluminum oxide or magnesium oxide,
The spin torque generating element according to claim 1, wherein the ferromagnetic layer is formed of a ferromagnetic material having a saturation magnetization of 10 kOe or more.
7. The spin torque generating element according to claim 1, wherein the conductor layer has a thickness of several nm or more and several tens of nm or less.
A conductor layer to which a current is supplied, an insulating layer formed on one surface of the conductor layer, and a ferromagnetic layer formed on the other surface of the conductor layer are provided. A method for manufacturing a spin torque generating element for generating a spin torque that acts on the magnetization of the ferromagnetic layer,
A first step of forming the ferromagnetic layer, the conductor layer, and the insulating layer with respective materials so that the ferromagnetic layer, the conductor layer, and the insulating layer are laminated in this order;
A second step of performing an annealing treatment for heating the stacked ferromagnetic layer, the conductor layer, and the insulating layer, the method for manufacturing a spin torque generating element.
The spin torque generation according to claim 8, wherein in the first step, the ferromagnetic layer is formed of iron or cobalt iron, the conductor layer is formed of copper, and the insulating layer is formed of aluminum oxide or magnesium oxide. Manufacturing method of device.
The method for manufacturing a spin torque generating element according to claim 8 or 9, wherein in the annealing treatment, the conductor layer, the insulating layer, and the ferromagnetic layer are heated at a temperature of 200 ° C or higher, 300 ° C or higher, or 400 ° C or higher. ..
A conductor layer to which a current is supplied, an insulating layer formed on one surface of the conductor layer, and a ferromagnetic layer formed on the other surface of the conductor layer are provided. A spin torque generating element that generates a spin torque that acts on the magnetization of the ferromagnetic layer,
A magnetization control device, comprising: a current supply device for supplying a current to the conductor layer,
The magnetization control device, wherein the current supply device controls the direction of magnetization of the ferromagnetic layer by the spin torque by causing a current to flow through the conductor layer.