JPWO2020090719A1 - Spin torque generator, its manufacturing method, and magnetization control device - Google Patents

Abstract

The spin torque generating element 10 includes a conductor layer 1 to which a current Jc is supplied, an insulating layer 2 formed on one surface of the conductor layer 1, and a ferromagnetic layer formed on the other surface of the conductor layer 1. And 3 are provided. The current in the conductor layer 1 generates a spin torque that acts on the magnetization of the ferromagnetic layer 3.

Description

The present invention relates to a spin torque generating element that generates a spin torque with respect to the magnetization of the ferromagnetic layer by a current flowing through the conductor layer. The present invention also relates to a method for 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, and when a current flows through the conductor layer, the spin torque acts on the magnetization of the ferromagnetic layer. Is an element that generates. This spin torque can change the direction of magnetization of the ferromagnetic layer. For example, the direction of magnetization can be reversed, or the precession of magnetization can be self-oscillated. Magnetic memories, microwave oscillators, spin wave logic, etc. that utilize such changes in the direction of magnetization have been proposed.

For example, Patent Document 1 discloses STT-MRAM (Spin-Transfer Torque Magnetic Random Access Memory) as a magnetic memory provided with 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 direction of magnetization formed of a ferromagnetic material. The reference layers to which are fixed are laminated in this order. When an external magnetic field is applied to this STT-MRAM in the stacking direction of each layer and a current is passed through the conductor layer, a spin current is generated in the conductor layer due to the spin Hall effect, and a spin torque due to the spin current acts as a recording layer. The direction of magnetization of is reversed.

International Publication No. 2016/021468

Seung Ryong Park at al, “Microscopic mechanism for the Rashba spin-band splitting: Perspective from formation of local orbital angular momentum”, pp.6-17, 201 (2015), Journal of Electron Spectroscopy and Related Phenomena

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

Conventionally, in order to generate a spin current, it is considered that the conductor layer needs to be formed of a heavy metal having a large spin-orbit coupling (SOC). For example, in Patent Document 1, the conductor layer is formed of heavy metals such as Hf, W, Re, Os, Ir, Pt, Pb, or alloys thereof. Such heavy metals have high electrical resistance, and the efficiency of passing an electric current through the conductor layer decreases accordingly. As a result, the efficiency of passing a current through the conductor layer to generate spin torque as described above becomes low. Further, heavy metal materials having a large specific density tend to be expensive and difficult to obtain.

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

The spin torque generating element 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. With
The current in the conductor layer generates a spin torque that acts on the magnetization of the ferromagnetic 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, which generates a spin torque acting on the magnetization of the ferromagnetic layer by a current of the conductor layer.
A first step of forming the ferromagnetic layer, the conductor layer, and the insulating layer with their respective materials so that the ferromagnetic layer, the conductor layer, and the insulating layer are laminated in this order.
The present invention includes 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 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 are provided, and the electric current of the conductor layer causes the conductor layer. , A spin torque generating element that generates a spin torque acting on the magnetization of the ferromagnetic layer,
A current supply device for passing a current through the conductor layer is provided.
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 to provide a conductor. By passing an electric current through the layer, it is possible to generate a spin torque that acts on the magnetization of the ferromagnetic 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, it is possible to generate spin torque by the current of the conductor layer without using a conductor layer having a large specific density.

The configuration of the spin torque generating element according to the embodiment of the present invention is shown. It is explanatory drawing of the spin torque generation principle in embodiment of this invention. The Periodic Table of the Elements is shown to explain the material of the conductor layer. A measuring device for measuring spin torque is shown. It is explanatory drawing of magnetic resonance used in the measurement of spin torque. For the example of the spin torque generating element, the voltage measurement value by the voltmeter and the symmetric component and the asymmetric component thereof are shown. For another embodiment of the spin torque generator, a voltage measurement by a voltmeter and its symmetric and asymmetric components are shown. The measurement result of the conversion efficiency with respect to the thickness of the conductor layer is shown. Another measurement result of the conversion efficiency with respect to the thickness of the conductor layer is shown. The measurement result of the conversion efficiency for the material of the ferromagnetic layer is shown. The measurement result of the conversion efficiency with respect to the heating temperature of the annealing treatment is shown. It is a flowchart which shows the manufacturing method of the spin torque generating element by embodiment of this invention. A schematic configuration of the magnetization control device according to the embodiment of the present invention is shown. It is explanatory drawing in the case of configuring a magnetization control device as a spin logic device. The operating characteristics of the spin torque generating elements constituting the spin logic device are shown. A configuration example of a magnetization control device as a spin logic device is shown. It is a table which shows the output digital signal with respect to the 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, the same reference numerals are given to common parts in each figure, and duplicate description is omitted.

(Outline of configuration of spin torque generator)
FIG. 1 shows the configuration of the spin torque generating element 10 according to the 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, a transition metal). The insulating layer 2 is formed of an insulating material on one surface of the conductor layer 1 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 are each metal material and insulating material that generate a spin torque acting on the magnetization of the ferromagnetic layer 3 by the current of the conductor layer 1. , And made of ferromagnetic material. According to the present embodiment, the conductor layer 1, the insulating layer 2, and the ferromagnetic layer 3 are made of metal materials, insulating materials, and ferromagnetic materials that cause a specific spin torque generating phenomenon described later in the spin torque generating element 10. It is formed. That is, these metal 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. A specific spin torque generation phenomenon in the spin torque generation element 10 occurs as follows. That is, as shown in FIG. 2, when the current Jc flows through the conductor layer 1, the orbital angular momentum of each electron (Orbital Angular Momentum) 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 a spin torque Ts acting on the magnetization M of the ferromagnetic layer 3. Here, the current Jc flows from one end to the other end of the conductor layer 1 along the interface 4. This 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 the orbital angular momentum of each electron is generated at the interface 4 by the current Jc flowing through the conductor layer 1 in the direction along the interface 4 in the spin torque generating element 10. Due to the action of 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 coupled (mixed), and as a result, the spin direction of the electrons in the ferromagnetic layer 3 changes. The direction of the magnetization M of the ferromagnetic layer 3 changes. For example, the magnetization M of the ferromagnetic layer 3 is inverted.

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

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

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

In the embodiment, the conductor layer 1 is made of copper (Cu). 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 metal element material included in the above range R1 (or the above range R2) of the Periodic Table of the Elements. The thickness of the conductor layer 1 may be several nm (for example, 4 nm or 5 nm) or more and several tens of 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 due to the above-mentioned orbital Rashba effect at the interface 4. In the examples, the insulating material forming the insulating layer 2 is aluminum oxide (Al ₂ O ₃ ) or magnesium oxide (Mg O).

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

As described above, in the embodiment of the present embodiment, the conductor layer 1 is formed of copper, the insulating layer 2 is formed of aluminum oxide or magnesium oxide, and the ferromagnetic layer 3 is formed 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 forming the conductor layer 1, the insulating layer 2, and the ferromagnetic layer 3, respectively, have the above-mentioned specific spins as described above. It may be selected as a combination of materials that cause a torque generation phenomenon. In this case, the metal material of the conductor layer 1 may be limited to the material of the metal element included in the range R1 of FIG. Such selection of the metal material, the insulating material, and the 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 of 0.05 or more, 0.1 or more, or 0.2, which will be described later. It may be selected as a combination of the above materials.

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

The measuring device 20 is a device using a 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 the 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 one of the electrodes 5a and the capacitor 6 via a coil 8. With this configuration, the voltmeter 9 measures the DC component (DC voltage) of the voltage generated at one of the electrodes 5a.

Further, in FIG. 4, in a coordinate system having x-axis, y-axis, and z-axis 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, an external magnetic field _Hext is applied by means (not shown). The direction of the external magnetic field _{Hex is} a direction orthogonal to the z-axis and forms an acute angle φ with the x-axis. The external magnetic field _Hext and the current of the conductor layer 1 excite magnetic resonance, which is the aging motion 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 X-axis, Y-axis, and Z-axis orthogonal to each other is fixed to the ferromagnetic layer 3, and these X-axis, Y-axis, and Z-axis are x in FIG. 4, respectively. It is parallel to the axis, y-axis, and z-axis. When a high-frequency current is applied to the conductor layer 1 in the x-axis direction, the torque _TF generated by the magnetic field itself acts on the magnetization M of the ferromagnetic layer 3 in the direction parallel to the Z-axis as shown in FIG. do. Further, the spin torque Ts 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 precesses around an axis oriented in the direction of the _{external magnetic field Next.}

<Voltage measurement result indicating the 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 symmetrical and asymmetric components. The results of FIGS. 6 and 7 were 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 for which the result of FIG. 6 was obtained, the conductor layer 1 was formed of Cu, the insulating layer 2 was _{formed of Al 2} O ₃ , and the ferromagnetic layer 3 was formed 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 for which the result of FIG. 7 was obtained, the conductor layer 1 was formed of Cu, the insulating layer 2 was formed of MgO, the ferromagnetic layer 3 was formed of CoFe, and the conductor layer 1 and the conductor layer 1 were formed. The thicknesses of the insulating layer 2 and the ferromagnetic layer 3 are 10.9 nm, 20 nm, and 5 nm, respectively.

In FIGS. 6 and 7, the horizontal axis represents _{the strength of the applied external magnetic field Hext} , and the vertical axis represents the voltage. In FIGS. 6 and 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. The single-point chain line 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.

The symmetric component and the asymmetric component were obtained according to a 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, since it is unlikely that the spin torque is generated by the spin current in copper having a small specific gravity, 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.

In FIGS. 6 and 7, it can be seen that a peak is generated in the symmetric 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 clear peak has a considerably large (that is, fairly efficient) spin by combining the materials of the conductor layer 1, the insulating layer 2, and the ferromagnetic layer 3 with Cu, MgO, and CoFe. It shows that torque is generated.

<Measurement result of conversion efficiency with respect to the thickness of the 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 by using the measuring device 20 of FIG. In FIGS. 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 to the spin torque of the conductor layer 1.

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 indicates the value of the spin current when it is assumed that the spin torque due to 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 is generated by the spin current in copper having a small specific gravity, so Js is a current corresponding to the spin torque due to the orbital angular momentum of the electrons generated at the interface 4. It can be said that.

Further, in FIG. 8, the plot of the square marks shows the case of the spin torque generating element 10 in which 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.} The circled plot shows a spin torque generating 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 plot shows a spin torque generating element 10 in which 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.

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 magnitude of the peak value of the conversion efficiency θ when the insulating layer 2 is Al ₂ O ₃ is more than twice the magnitude of 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 when the insulating layer 2 is Al ₂ O ₃ , a large conversion efficiency θ can be obtained.

Further, as can be seen from FIGS. 8 and 9, the magnitude of 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, a conversion efficiency θ further improved as compared with the case _{where the insulating layer 2 is Al 2} O _{3 can be obtained.}

Further, as shown in FIGS. 8 and 9, when the insulating layer 2 is Al ₂ O ₃ or Mg O, the conversion efficiency θ depends on the thickness of the conductor layer 1. Therefore, _{it can be seen that the conversion of the current JC} to the spin torque is caused by the presence 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 thickness of the conductor layer 1 may be a value within the range of 5 nm or more and 19 nm or less. In this case, in FIG. 8, the conversion efficiency θ with respect to the plot of the square mark is a value of less than 0.05 or less. Further, 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 with respect to the plot of the square mark is a value of about 0.10 or more. Further, the thickness of the conductor layer 1 may be a value within the range of 9 nm or more and 13 nm or less. In this case, in FIG. 8, the conversion efficiency θ related to the plot of the square mark is a value near the maximum value (a little less than 0.13).

An example of the numerical range of the thickness of the conductor layer 1 in the case where 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 thickness of the conductor layer 1 may be a value within the range 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 related to the plot of the square mark is 0.05 or more. Further, the thickness of the conductor layer 1 may be a value within the range of 6 nm or more and 26 nm or less. In this case, in FIG. 9, the conversion efficiency θ with respect to the plot of the square mark is a value larger than 0.10. Further, 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 related to the plot of the square mark is a value near the maximum value (a little less than 0.25).

<Measurement result of conversion efficiency for material of ferromagnetic layer>
FIG. 10 shows the measurement result of the conversion efficiency θ with respect to the material of the ferromagnetic layer 3 obtained by using the measuring device 20 of FIG. That is, FIG. 10 shows the measurement in each case where the conductor layer 1 is formed of Cu and the insulating layer 2 is _{formed of Al 2} O ₃ in the spin torque generating element 10, but the material of the ferromagnetic layer 3 is changed. The result is 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 attached to the arrow pointing to the black circle.

As shown in FIG. 10, when the ferromagnetic layer 3 was formed of CoFe, the highest conversion efficiency θ (a little less than 0.13) was obtained. 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 was zero or almost zero.

As described above, it can be seen that the above-mentioned 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 each in a specific combination. In the examples of FIGS. 6 to 10, the above-mentioned orbital Rashba effect is obtained when the _{combination is Cu and Al 2} O ₃ and CoFe, Cu and Al ₂ O _{3 and Fe, or Cu and Mg O and CoFe.} It was confirmed that. However, according to the present embodiment, if the orbital Rashba effect is obtained, the combination of the materials forming the conductor layer 1, the insulating layer 2, and the ferromagnetic layer 3 may be other combinations (for example, Cu, MgO, and Fe, respectively). There may be.

Further, when the conductor layer 1 is formed of Cu and the insulating layer 2 is formed of Al ₂ O ₃ or Mg O, 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 constituting the spin torque generating element 10 after production (before or after annealing treatment described later). ) Saturation magnetization, and may be a value at room temperature.

<Measurement result of conversion efficiency for annealing treatment>
FIG. 11 shows the measurement results of the conversion efficiency θ with respect to the heating temperature of the annealing treatment, which was obtained by using the measuring device 20 of FIG. FIG. 11 shows a case where 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. However, when the annealing treatment is performed at each heating temperature. The measured value of the above 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 are laminated by vapor deposition and then heated for 30 minutes at the temperature indicated by the arrow pointing to the black circle. 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 circle indicated by the arrow with “NO ANNEALING” indicates the measured value when the annealing treatment is 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 improved more than twice and approached 0.3. In this way, the annealing process makes it possible to maximize the conversion efficiency θ.

In the spin torque generating element 10 according to each embodiment, as shown below, the resistivity of the conductor layer 1 is significantly smaller than the resistivity of a heavy metal such as tungsten (W), so that the spin torque generation efficiency is increased accordingly. It can be said that it is expensive. The conversion efficiency θ obtained by the annealing treatment at 400 ° C. as described above is a value equivalent to that in the case where tungsten is used for the conductor layer in the conventional spin torque generating element described above. Since the resistivity of the thin-film tungsten having a nanoscale thickness is approximately 12 times or more the resistivity of the thin-film copper having a nanoscale thickness, the conductor layer 1 of the spin torque generating element 10 according to each embodiment The electrical resistance of the film is small accordingly. As a result, in each embodiment, it can be said that the spin torque generation efficiency is improved by 12 times or more as compared with the above-mentioned 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 to be used are other combinations, an 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 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 treatment was not performed.

(Manufacturing method of 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 the respective materials so that the ferromagnetic layer 3, the conductor layer 1, and the insulating layer 2 are laminated in this order. This lamination may be carried out by a thin film deposition method. For example, the ferromagnetic layer 3 is formed by adhering a ferromagnetic material that has been heated and evaporated to the surface of a substrate. Next, the insulating layer 2 is formed by adhering the heat-evaporated insulating material to the surface of the ferromagnetic layer 3. Then, the conductor layer 1 is formed by adhering the heat-evaporated metal material to the surface of the insulating layer 2. As a result, a laminate having the ferromagnetic layer 3, the conductor layer 1, and the insulating layer 2 can be 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 and the conductor layer 1 and the insulating layer 2 are respectively formed with CoFe (or Fe) and Cu and _Al 2 _{O 3,} or CoFe (or Fe) and Cu and MgO However, it may be made of other materials.

In step S2, an annealing treatment (for example, 30 minutes) is performed to heat the conductor layer 1, the insulating layer 2, and the ferromagnetic layer 3 laminated in step S1. 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.

(Effect of embodiment)
According to the spin torque generating 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. In 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, it is possible to generate spin torque 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 material of a metal element within the range R1 or R2 of the periodic table of FIG. 3). NS. The metal material (eg copper) tends to be readily 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 electrical resistivity. Therefore, the efficiency of generating spin torque Ts is improved accordingly. Further, by performing the above-mentioned annealing treatment, the conversion efficiency from the current of the conductor layer 1 to the spin torque Ts is improved.

Therefore, the spin torque generating element 10 having a very high conversion efficiency can be mass-produced 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 spin torque generating element 10 described above and a current supply device 11 for passing a current through the conductor layer 1. The current supply device 11 allows a current to flow through the conductor layer 1 in a direction along the interface 4 from one end to the other end of the spin torque generating element 10, or from the other end to one end of the spin torque generating element 10. A current is passed through the conductor layer 1 in the direction toward the direction, and the direction of the magnetization M of the ferromagnetic layer 3 is controlled by the spin torque Ts generated by the current. 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 generate the precession, the magnetization control device 100 _{applies an external magnetic field Hext in the} direction of the central axis of the precession (for example, a permanent magnet or an electromagnet) 12 May be equipped.

<Example of application to magnetic memory>
The magnetization control device 100 may constitute 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 above-mentioned magnetic field application unit 12 may be omitted. The reference layer 13 is made 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 orientation of the magnetization of the reference layer 13 (hereinafter simply referred to as the magnetization Mr) is fixed.

The current supply device 11 causes the 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 electron trajectory due to the above-mentioned 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 that of the magnetization Mr, or opposite to that of the magnetization Mr.

The magnetization control device 100 includes 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 writing command. That is, the current supply device 11 passes a current through each of the conductor layers 1 of the one or a plurality of the spin torque generating elements 10 as described above in accordance with the writing command, and the magnetization M of the ferromagnetic layer 3 of the element 10 is passed. Reverse the direction of. One-bit data of "0" and "1" is assigned to two types of directions of the magnetization M of the ferromagnetic layer 3 in each element 10, and the data is stored in a large number of 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 generating element 10, a read current is passed between the electrode (not shown) provided on the reference layer 13 and the electrode (not shown) provided on the ferromagnetic layer 3, and the read current is transferred. 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 recorded data based on the detected value.

<Example of application to microwave oscillator>
The magnetization control device 100 shown in FIG. 13 may constitute a microwave oscillator. 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 generates microwaves by the change in the direction of the magnetization M.

For example, the current supply device 11 repeatedly reverses the direction of the magnetization M of the ferromagnetic layer 3 by passing an alternating current through the conductor layer 1 in one direction (for example, the left-right direction in FIG. 13) along the interface 4. Generate waves. In this case, the reference layer 13 and the magnetic field application unit 12 may be omitted.

Alternatively, the current supply device 11 causes a current to flow through the conductor layer 1 in a direction along the interface 4 (for example, the left-right direction in FIG. 13), and the magnetic field application unit 12 sends an external magnetic field _ext to the ferromagnetic layer 3 to the interface 4. It is applied in a direction along the line (for example, a direction forming a sharp 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 Hex as the central axis.} As a result, microwaves are generated.

<Application to logic devices>
FIG. 14 is an explanatory diagram when the above-mentioned magnetization control device 100 is configured as a spin logic device. In this case, the magnetization control device 100 further measures a voltage between the voltage applying device 14 for applying a gate voltage between the conductor layer 1 and the insulating layer 2 and the voltage between the ferromagnetic layer 3 and the reference layer 13. A total of 15 are provided. The above-mentioned magnetic field application unit 12 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 constituting the spin logic device. In FIG. 15, the horizontal axis indicates the value of the current flowing through the conductor layer 1 by the current supply device 11, and the positive / negative of this current value indicates the direction of the current (right direction and left direction in FIG. 14). In FIG. 15, the vertical axis represents the value of the voltage measured by the voltmeter 15. On the vertical axis of FIG. 15, the measured voltage value of 1.0 (arb.) Is one of the two directions in which the magnetization of the ferromagnetic layer 3 is opposite to each other (for example, the right direction in FIG. 14). That is, the fact that the measured voltage value is −1.0 (arb.) Indicates that it is the other of the above two directions (for example, the left direction in FIG. 14). In addition, "arb." Indicates an arbitrary unit (the same applies hereinafter).

15, a chain line a thick one-dot shows the operation characteristics of a state whose value is + V _G of the gate voltage of the above, and a thick line, the operating characteristics of a state value of the gate voltage of the above is -V _G show. Switching the direction of magnetization of the ferromagnetic layer 3 is performed according to the thick solid line in FIG. 15, but is not performed according to the thick alternate long and short dash line in FIG. 15 (that is, the absolute value is from 6 (arb.)). A current (largely smaller than 7 (arb.)) Is passed through the conductor layer 1 by the current supply device 11.

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 (hereinafter, also referred to as set A and set B) of spin torque generating elements 10 sharing 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 and B has the operating characteristics shown in FIG.

The voltage application device 14 and the voltmeter 15 described above are provided for each of the sets A and B. The voltage application device 14 and the voltmeter 15 of one group A are described as the voltage application device 14A and the voltmeter 15A, respectively, and the voltage application device 14 and the voltmeter 15 of the other group B are described as the voltage application device 14B and the voltmeter 15B, respectively. It is described as.

For gate voltages above + the V _G as an input digital signal of "1", the -V _G as an input digital signal of "0". In a state where the current supply device 11 is passing a current having the above-mentioned intermediate value (for example, −6.5 (arb.)) Into the conductor layer 1, the voltage applying device 14A applies a gate voltage to the set A. , + _{V G} and -V _G (i.e., a "1" digital signal "0") switched between a voltage applying device 14B, a gate voltage to be applied to the set B, + _{V G} and -V _G When switching between, the output digital signals for the two input digital signals are as shown in the table shown in FIG. 17, the set A, the gate voltage to B "1" and "0", respectively mean + _{V G} and _{-V G, V T (arb.} ) , The voltage voltmeter 15A, 15B measures It means the total _V T values (arb.).

The magnetization control device 100 further includes an output unit 16 that outputs an output digital signal with respect to the above-mentioned two input digital signals. When the output unit 16 is configured as a logical sum (OR), the voltage measurement value of the voltmeter 15A and the voltage measurement value of the voltmeter 15B are both 0 as in the case of the logical sum (OR) of FIG. In the case of (arb.), The digital signal of "0" is output, and in other cases, the digital signal of "1" is output. On the other hand, when the output unit 16 is configured as a logical product (AND), the voltage measurement value of the voltmeter 15A and the voltage measurement value of the voltmeter 15B are either as shown in the “logical product case” of FIG. If also 1 (arb.), The digital signal of "1" is output, and in other cases, the digital signal of "0" is output.

The output unit 16 may be configured as follows, for example, in order to output a digital signal as shown in FIG. The current supply device 11 passes a current whose absolute value is fixed to the above intermediate value and whose sign is fixed to negative to the conductor layer 1. Because of the current in the conductor layer 1, each set A, the magnetization reversal of the ferromagnetic layer 3 of B is induced, total _V T of the voltage measurement from voltmeter 15A, 15B (arb.), Each magnetization It changes from -2 (arb.) To 2 (arb.) As shown in FIG. 17 depending on the state and the above-mentioned gate voltage. 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 When) is smaller than the reference voltage, the output unit 16 outputs the digital signal “1”. Similarly, in the case of the logical product, define a reference voltage and _{-1 (arb.), V T} (arb.) When is greater than the reference voltage, the output unit 16 outputs a digital signal "0", when total _V T (arb.) is less than the reference voltage, the output unit 16 outputs a digital signal "1". Incidentally, in a state in which the absolute value of the negative current is the intermediate value is flowing in the conductor layer 1, such that the total V _T according to Figure 17 with respect to the gate voltage of the above _(arb.) Is obtained, see The direction of magnetization of layer 13 is set.

<Application to magnetic sensors>
FIG. 18 shows a configuration example when the above-mentioned magnetization control device 100 is a magnetic sensor. In the example of FIG. 18, the magnetization control device 100 includes first to fourth spin torque generating elements 10A to 10D. Each of these spin torque generating elements 10A to 10D has 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 made of, for example, SiO ₂ . The reference layer 13 and the magnetic field application unit 12 may be omitted.

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

One ends in the x-axis direction of the conductor layers 1 of the first and second spin torque generating elements 10A and 10B are connected to each other by a conductive line 18a, and the third and fourth spin torque generating elements 10C and 10D are connected to each other. One ends of the conductor layer 1 in the x-axis direction are also connected to each other by a 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 a conductive line 18d.

The current supply device 11 applies an alternating current between the conductive lines 18a and the conductive lines 18b. As a result, an alternating current flows in the conductor layer 1 of each spin torque generating element 10A to 10D in the x-axis direction. The direction of magnetization of the ferromagnetic layer 3 in each spin torque generating element 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 alternating current is applied between the conductive line 18a and the conductive line 18b by the current supply device 11, and an external magnetic field Hy in the y-axis direction exists in the magnetic sensor, the voltage measured by the voltmeter 18 is external. The value corresponds 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 geomagnetic component in the y-axis direction also changes as the attitude of the magnetic sensor (board 17) with respect to the ground changes. Therefore, this change can be detected based on the output voltage value of the magnetometer 18. Therefore, since the posture of the magnetic sensor can be detected, the posture of the object to which the magnetic sensor is attached can also be detected.

The present invention is not limited to the above-described embodiment, 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 above-mentioned plurality of items, or may have only a part of the above-mentioned plurality of items. good. Further, the spin torque generating element 10, the manufacturing method thereof, and the magnetization control device 100 may not exhibit all of the above-mentioned effects and effects, or may exhibit only a part of the above-mentioned effects.

1 Conductor layer, 2 Insulation layer, 3 ferromagnetic layer, 4 interface, 5a, 5b electrodes, 6 capacitors, 7 AC power supply, 8 coils, 9 voltmeter, 10 spin torque generator, 11 current supply device, 12 magnetic field application part , 13 Reference layer, 14, 14A, 14B voltage application device, 15, 15A, 15B voltmeter, 16 output unit, 17 board, 18 voltmeter, 20 measuring device, 100 magnetization control device

Claims (11)

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 are provided.
The current in the conductor layer generates a spin torque that acts on the magnetization of the ferromagnetic layer.
Spin torque generating element. The conductor layer, the insulating layer, and the ferromagnetic layer are each made of a material that causes a specific spin torque generating phenomenon in the spin torque generating element.
In the specific spin torque generation phenomenon, when a current flows through the conductor layer, the orbital angular momentum of electrons is generated at the interface between the conductor layer and the insulating layer due to the orbital rushba effect, and the orbital angular momentum is the ferromagnetism. The spin torque generating element according to claim 1, which is a phenomenon of generating a spin torque acting on the magnetization of a layer. The spin torque generating element according to claim 1 or 2, wherein the conductor layer is made of a material of a metal element belonging to the range from the second period to the 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 or 2, wherein the conductor layer is formed of copper, the insulating layer is formed of aluminum oxide or magnesium oxide, and the ferromagnetic layer is formed of iron or cobalt iron. The conductor layer is made of copper and the insulating layer is made of aluminum oxide or magnesium oxide.
The spin torque generating element according to claim 1 or 2, wherein the ferromagnetic layer is made of a ferromagnetic material having a saturation magnetization of 10 kOe or more. The spin torque generating element according to any one of claims 1 to 6, wherein the thickness of the conductor layer is several nm or more and several tens of nm or less. 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 are provided, and the electric current of the conductor layer causes the conductor layer. A method for manufacturing a spin torque generating element that generates a spin torque acting on the magnetization of the ferromagnetic layer.
A first step of forming the ferromagnetic layer, the conductor layer, and the insulating layer with their respective materials so that the ferromagnetic layer, the conductor layer, and the insulating layer are laminated in this order.
A method for manufacturing a spin torque generating element, comprising a second step of performing an annealing treatment for heating the laminated ferromagnetic layer, the conductor layer, and the insulating layer. 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. Method of manufacturing the element. 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 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 are provided, and the electric current of the conductor layer causes the conductor layer. , A spin torque generating element that generates a spin torque acting on the magnetization of the ferromagnetic layer,
A magnetization control device including a current supply device for passing a current through the conductor layer.
The current supply device is a magnetization control device that controls the direction of magnetization of the ferromagnetic layer by the spin torque by passing a current through the conductor layer.

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