Spin wave devices

Abstract

This can suppress noise in relation to spin waves. [Solution] The spin wave device 1 comprises a first conductor 10 that excites a first spin wave by applying a first alternating current, a second conductor 20, and a waveguide 30 that propagates the first spin wave in a first direction from the first conductor 10 to the second conductor 20. The direction of the first alternating current flowing through the first conductor 10 and the first direction are non-orthogonal.

Description

Technical Field

[0001] The present disclosure relates to spin-wave devices.

Background Art

[0002] Patent Document 1 and Non-Patent Documents 1 and 2 disclose techniques for detecting spin waves.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Non-Patent Documents

[0004]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the above prior art, spin waves are generated in a waveguide by supplying alternating current power to an excitation electrode or antenna. At this time, an electromagnetic wave propagating in the atmosphere is generated by the current flowing through the excitation electrode or antenna. The generated electromagnetic wave can become noise with respect to the spin wave.

[0006] Therefore, this disclosure provides a spin wave device that can suppress noise to spin waves. [Means for solving the problem]

[0007] A spin wave device according to one aspect of the present disclosure comprises a first conductor that excites a first spin wave by applying a first alternating current, a second conductor, and a waveguide that propagates the first spin wave in a first direction from the first conductor to the second conductor, wherein the direction of the first alternating current flowing through the first conductor and the first direction are non-orthogonal. [Effects of the Invention]

[0008] According to this disclosure, noise on spin waves can be suppressed. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 shows the configuration of a spin wave device according to Embodiment 1. [Figure 2] Figure 2 is a plan view showing the positional relationship between the waveguide and the conductor of the spin wave device according to Example 1. [Figure 3] Figure 3 is a cross-sectional view showing the positional relationship between the waveguide and the conductor of the spin wave device according to Embodiment 1. [Figure 4] Figure 4 is a plan view showing the positional relationship between the waveguide and the conductor of the spin wave device according to Example 2. [Figure 5] Figure 5 is a plan view showing the positional relationship between the waveguide and conductor of a spin wave device according to a comparative example. [Figure 6] Figure 6 shows the magnitudes of electromagnetic waves and spin waves detected by the comparative example and the spin wave devices according to Examples 1 and 2. [Figure 7] Figure 7 shows the configuration of the spin wave device according to Embodiment 2. [Figure 8] Figure 8 is a plan view showing the positional relationship between the waveguide and the conductor of the spin wave device according to Embodiment 2.

Best Mode for Carrying Out the Invention

[0010] (Summary of the Present Disclosure) The spin-wave device according to the first aspect of the present disclosure includes a first conductor that excites a first spin wave by applying a first alternating current, a second conductor, and a waveguide that propagates the first spin wave in a first direction from the first conductor toward the second conductor, wherein the direction of the first alternating current flowing through the first conductor and the first direction are non-orthogonal.

[0011] The electromagnetic wave generated by the first alternating current flowing through the first conductor mainly propagates in a direction orthogonal to the direction of the first alternating current. In the spin-wave device according to this aspect, since the direction of the first alternating current and the first direction, that is, the propagation direction of the first spin wave, are non-orthogonal, the propagation direction of the electromagnetic wave and the propagation direction of the first spin wave do not coincide. Thereby, noise with respect to the first spin wave can be suppressed.

[0012] The spin-wave device according to the second aspect of the present disclosure is the spin-wave device according to the first aspect of the present disclosure, wherein the angle formed by the direction of the first alternating current flowing through the first conductor and the first direction is 45 degrees or less.

[0013] Thereby, the propagation direction of the electromagnetic wave and the propagation direction of the first spin wave can be made significantly different, so that noise can be further suppressed.

[0014] The spin-wave device according to the third aspect of the present disclosure is the spin-wave device according to the first or second aspect of the present disclosure, and includes a magnetic field source that applies a bias magnetic field to the waveguide.

[0015] Thereby, a bias magnetic field can be applied to the waveguide, so that it is possible to facilitate the excitation of spin waves.

[0016] The spin-wave device according to the fourth aspect of the present disclosure is the spin-wave device according to the third aspect of the present disclosure, wherein the direction of the bias magnetic field is parallel to the first direction.

[0017] This makes it easier to excite spin waves.

[0018] A spin wave device according to a fifth aspect of this disclosure is a spin wave device according to any one of the first to fourth aspects of this disclosure, wherein the waveguide mainly comprises yttrium iron garnet.

[0019] This allows spin waves to propagate efficiently.

[0020] A spin wave device according to a sixth aspect of this disclosure is a spin wave device according to any one of the first to fifth aspects of this disclosure, wherein the direction of the current flowing through the second conductor by the first spin wave and the first direction are non-orthogonal.

[0021] This makes it more difficult for the second conductor to detect electromagnetic waves, thus further suppressing noise. Therefore, the detection accuracy of the first spin wave by the second conductor can be improved.

[0022] A spin wave device according to a seventh aspect of this disclosure is a spin wave device according to a sixth aspect of this disclosure, wherein the path of the first alternating current flowing through the first conductor and the path of the current flowing through the second conductor by the first spin wave are located on the same straight line.

[0023] This makes it possible to further improve the detection accuracy of the first spin wave by the second conductor.

[0024] A spin wave device according to the eighth aspect of this disclosure is a spin wave device according to any one of the first to seventh aspects of this disclosure, comprising a third conductor that excites a second spin wave by the application of a second alternating current, wherein the waveguide propagates the second spin wave in a second direction from the third conductor to the second conductor, the first conductor, the second conductor and the third conductor are arranged in this order, and the direction of the second alternating current flowing through the third conductor and the second direction are non-orthogonal.

[0025] This allows for the use of interference between the first and second spin waves, thereby improving the accuracy of spin wave detection.

[0026] The embodiments will be described in detail below with reference to the drawings.

[0027] The embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, arrangement and connection configurations of components, steps, and the order of steps shown in the following embodiments are examples only and are not intended to limit this disclosure. Furthermore, any components in the following embodiments that are not described in an independent claim will be described as optional components.

[0028] Furthermore, each figure is a schematic diagram and not necessarily a strictly accurate representation. Therefore, for example, the scale may not necessarily match in each figure. Also, in each figure, substantially identical components are given the same reference numerals, and redundant explanations are omitted or simplified.

[0029] Furthermore, in this specification, terms indicating relationships between elements such as parallel and perpendicular, terms indicating the shapes of elements such as rectangles and squares, and numerical ranges do not represent only strict meanings, but also include substantially equivalent ranges, such as differences of a few percent.

[0030] Furthermore, in this specification, the terms "upper" and "lower" do not refer to the upward (vertically upward) and downward (vertically downward) directions in absolute spatial perception, but rather are used as terms defined by the relative positional relationship based on the stacking order in a stacked configuration. Moreover, the terms "upper" and "lower" apply not only when two components are spaced apart and another component exists between them, but also when two components are placed in close proximity and touching each other.

[0031] Furthermore, in this specification and the drawings, the x, y, and z axes represent the three axes of a three-dimensional Cartesian coordinate system. In this specification, the z axis is perpendicular to the main surface of the membrane waveguide. Also, in this specification, "plan view" means the view from a direction perpendicular to the main surface of the membrane waveguide, that is, the view from the positive or negative side of the z axis.

[0032] Furthermore, in this specification, "main component" refers to the component with the highest content among all components constituting the material. For example, a component with a content of 50% or more is the main component. Components include materials, elements, or compounds.

[0033] Furthermore, in this specification, ordinal numbers such as "first," "second," etc., do not mean the number or order of components unless otherwise specified, but are used to avoid confusion and to distinguish similar components.

[0034] (Embodiment 1) [composition] First, the configuration of the spin wave device according to Embodiment 1 will be explained using Figure 1. Figure 1 is a diagram showing the configuration of the spin wave device 1 according to Embodiment 1.

[0035] The spin wave device 1 is a device that generates spin waves within the waveguide 30. The spin wave device 1 according to this embodiment is a magnetic sensor that detects magnetism (magnetic field) by utilizing the fact that the physical properties of spin waves change with a magnetic field. The detectable magnetism is the weak magnetic field generated by living organisms, such as the brain's magnetic field.

[0036] As shown in Figure 1, the spin wave device 1 comprises a first conductor 10, a second conductor 20, and a waveguide 30. Furthermore, the spin wave device 1 comprises an AC power supply 40, a voltage measuring instrument 50, and a magnetic field source 60.

[0037] The first conductor 10 excites a spin wave when an alternating current is applied. The first conductor 10 is also called an excitation electrode or excitation antenna. The alternating current applied to the first conductor 10 is an example of a first alternating current, and the spin wave excited by this alternating current is an example of a first spin wave. The spin wave is a surface wave, but it may also be a back volume wave or a front volume wave. In the case of a surface wave or a back volume wave, detection accuracy can be improved even if the bias magnetic field generated by the magnetic field source 60 is small.

[0038] The first conductor 10 includes a power supply point 11 to which an alternating current is applied, and a grounding point 12 connected to ground potential. An alternating current flows between the power supply point 11 and the grounding point 12. The path of the alternating current can be considered as a straight line connecting the power supply point 11 and the grounding point 12. The direction of the alternating current is parallel to the straight line connecting the power supply point 11 and the grounding point 12. In this embodiment, the direction parallel to the direction of the alternating current flowing through the first conductor 10 is defined as the x-axis. The plan view shape of the first conductor 10 is a long rectangle along the x-axis, but is not limited to this. The plan view shape of the first conductor 10 may be a square or a circle.

[0039] The second conductor 20 detects spin waves propagated through the waveguide 30. The second conductor 20 is also referred to as a detection electrode or detection antenna.

[0040] The second conductor 20 includes a detection point 21 where the voltage (potential) changes in response to a spin wave, and a grounding point 22 connected to ground potential. A spin wave is a fluctuation in a magnetic material and induces temporal oscillations of magnetic flux. Therefore, an induced electromotive force is generated in the second conductor 20, which is placed in close proximity to the waveguide 30 containing the magnetic material, due to the temporal oscillations of magnetic flux caused by the spin wave, according to the law of electromagnetic induction. By detecting the electrical signal based on the generated induced electromotive force, the spin wave can be detected. Specifically, the voltage (potential) at the detection point 21 of the second conductor 20 fluctuates due to the induced electromotive force, and a current flows through the second conductor 20. In this specification, the current flowing through the second conductor 20 due to the spin wave may be referred to as the detection current. The path of the current flowing through the second conductor 20 can be considered as a straight line connecting the detection point 21 and the grounding point 22. The direction of the current flowing through the second conductor 20 is parallel to the straight line connecting the detection point 21 and the grounding point 22. The plan view shape of the second conductor 20 is a long rectangle along the x-axis, but is not limited to this. The plan view shape of the second conductor 20 may be a square or a circle.

[0041] The first conductor 10 and the second conductor 20 mainly consist of conductive materials such as metals. For example, the first conductor 10 and the second conductor 20 mainly consist of Au, Ag, Cu, Al, Pt, or C.

[0042] The first conductor 10 and the second conductor 20 are spaced apart from each other and provided on the waveguide 30. The first conductor 10 and the second conductor 20 are in contact with the waveguide 30, but are not limited to that. The first conductor 10 and the second conductor 20 do not have to be in contact with the waveguide 30; for example, they may be provided on an insulating film covering the surface of the waveguide 30. Alternatively, the first conductor 10 and the second conductor 20 may be arranged in a floating state relative to the waveguide 30.

[0043] Waveguide 30 propagates spin waves. Waveguide 30 is also called the spin wave propagation layer. In this embodiment, waveguide 30 propagates the first spin wave in a first direction from the first conductor 10 to the second conductor 20. The first direction is also called the first spin wave propagation direction.

[0044] In this embodiment, the direction of the alternating current flowing through the first conductor 10 and the direction of first spin wave propagation are non-orthogonal. Specifically, the angle between the direction of the alternating current flowing through the first conductor 10 and the direction of first spin wave propagation is 45 degrees or less. For example, the angle between the direction of the alternating current flowing through the first conductor 10 and the direction of first spin wave propagation may be 10 degrees or less, or 5 degrees or less, and may be substantially 0 degrees. In other words, the direction of the alternating current flowing through the first conductor 10 and the direction of first spin wave propagation may be parallel.

[0045] Waveguide 30 includes, for example, at least one selected from the group consisting of ferromagnetic materials and antiferromagnetic materials. Ferromagnetic materials and antiferromagnetic materials are capable of propagating spin waves. Waveguide 30 may include only ferromagnetic materials from among ferromagnetic materials and antiferromagnetic materials. Waveguide 30 may include only antiferromagnetic materials from among ferromagnetic materials and antiferromagnetic materials. Waveguide 30 may include both ferromagnetic materials and antiferromagnetic materials. Specifically, waveguide 30 may be a structure in which layers of ferromagnetic material and layers of antiferromagnetic material are laminated.

[0046] As a ferromagnetic material, Y3Fe5O 12 (Yttrium iron garnet), (Y,Bi)3Fe5O 12 Lu3Fe5O 12 , (Ni, Zn)(Fe, Al)2O4, Mg(Fe, Al)2O4, Li 0.5 Fe 2.5 O4, (La,Sr)MnO3, Fe, Co, Ni, NiFe (permalloy), CoFe, CoFeB, CoNi, GdCo, etc. can be used. As an antiferromagnetic material, NiO x Cr2O3, YMnO3, etc., can be used. In this embodiment, the waveguide 30 contains yttrium iron garnet as its main component.

[0047] In this embodiment, the waveguide 30 is an insulator or dielectric. With this configuration, the spin wave device 1 can be easily operated as a magnetic sensor without providing an insulator or dielectric between the first conductor 10 and the second conductor 20 and the waveguide 30, separately from the waveguide 30. This is advantageous from the viewpoint of realizing a low-cost magnetic sensor.

[0048] The AC power supply 40 is electrically connected to the feed point 11 of the first conductor 10 and supplies an AC current from the feed point 11 to the first conductor 10. For example, a signal generator can be used as the AC power supply 40. The frequency of the AC current is in the GHz band, but is not limited to this.

[0049] The voltage measuring instrument 50 is electrically connected to the detection point 21 of the second conductor 20 and measures the change in voltage at the detection point 21 of the second conductor 20. For example, the voltage measuring instrument 50 can be a voltmeter, an oscilloscope, or a detection circuit.

[0050] The magnetic field source 60 applies a bias magnetic field to the waveguide 30. In this embodiment, the bias magnetic field is a static magnetic field. The magnitude of the bias magnetic field is, for example, 80 mT or less. The magnitude of the bias magnetic field is, for example, 40 mT or more.

[0051] As the magnetic field source 60, an electromagnet or a permanent magnet can be used. For example, the magnetic field source 60 includes two electromagnets arranged on either side of the waveguide 30. The direction of the bias magnetic field generated by the magnetic field source 60 is parallel to the first spin wave propagation direction. For example, the electromagnet includes a wheel with a diameter of 5 cm and enameled wire wound around the wheel. The diameter of the enameled wire is 0.2 mm and the number of turns is 200, but is not limited to these.

[0052] When operating the spin wave device 1, first, the AC power supply 40 applies an AC current to the feed point 11 of the first conductor 10. The application of the AC current excites a spin wave in the first conductor 10. At this time, a bias magnetic field is applied to the waveguide 30 by the magnetic field source 60, so the excitation of the spin wave can be performed efficiently.

[0053] The excited spin wave propagates through the waveguide 30 in a first direction from the first conductor 10 to the second conductor 20. The spin wave propagating through the waveguide 30 induces an electromotive force in the second conductor 20 according to the law of electromagnetic induction, causing a current to flow between the detection point 21 and the ground point 22. This changes the voltage at the detection point 21, which can then be detected by the voltage measuring instrument 50. Since the voltage change at the detection point 21 depends on the physical properties of the spin wave, detecting the voltage change enables the detection of the spin wave.

[0054] The spin wave device 1 according to this embodiment does not necessarily have to include an AC power supply 40, a voltage measuring instrument 50, and a magnetic field source 60. Depending on its intended use, the spin wave device 1 may be configured to electrically connect a power supply for exciting spin waves to the first conductor 10, and to electrically connect a device or circuit for detecting or processing signals generated in the second conductor 20 by the spin waves to the second conductor 20. For example, instead of the AC power supply 40 and the voltage measuring instrument 50, the spin wave device 1 may be provided with connection terminals or connectors for electrically connecting the AC power supply 40 and the voltage measuring instrument 50.

[0055] [Examples] Next, we will describe a specific example of the spin wave device 1 mentioned above.

[0056] <Example 1> Figures 2 and 3 are a plan view and a cross-sectional view, respectively, showing the positional relationship between the waveguide 30 and the first conductor 10 and the second conductor 20 of the spin wave device 1A according to Embodiment 1. Specifically, Figure 3 shows an xz cross-section along the dashed line L shown in Figure 2.

[0057] As shown in Figure 3, the spin wave device 1A according to Example 1 includes a support substrate 32 that supports the waveguide 30. The support substrate 32 is, for example, a gadolinium gallium garnet substrate (Gd3Ga5O 12The substrate is not particularly limited as long as it can support the waveguide 30. The planar shape of the support substrate 32 is a long rectangle in the x-axis direction. The support substrate 32 may have, for example, a length (in the x-axis direction) of 12 mm, a width (in the y-axis direction) of 2 mm, and a thickness (in the z-axis direction) of 0.5 mm, but is not limited to these dimensions.

[0058] The waveguide 30 is, for example, a yttrium iron garnet film. The waveguide 30 is formed on the upper surface of the support substrate 32 by a liquid-phase epitaxial method. The plan view shape of the waveguide 30 is a long rectangle in the x-axis direction, and the plan view size of the waveguide 30 is the same as the plan view size of the support substrate 32. The thickness of the waveguide 30 is, for example, 10 μm. However, the size and shape of the waveguide 30 are not particularly limited.

[0059] The spin wave device 1A includes a printed circuit board 70 that supports a first conductor 10 and a second conductor 20. A conductive thin film is formed on the upper surface of the printed circuit board 70 by sputtering, vapor deposition, or plating using a conductive material such as metal. The first conductor 10 and the second conductor 20 can be formed by patterning the formed conductive thin film using photolithography and etching. For example, the first conductor 10 and the second conductor 20 are copper films.

[0060] The first conductor 10 and the second conductor 20 are each elongated rectangles along the x-axis. For example, the first conductor 10 and the second conductor 20 each have a length (in the x-axis direction) of 300 μm, a width (in the y-axis direction) of 75 μm, and a thickness (in the z-axis direction) of 18 μm. The size and shape of the first conductor 10 and the second conductor 20 are not particularly limited.

[0061] As shown in Figure 3, a back electrode 80 is provided on the back surface of the printed circuit board 70. The back electrode 80 is set to ground potential. The back electrode 80 is a conductive thin film, such as a copper film, but is not limited to this.

[0062] Furthermore, the printed circuit board 70 is provided with via conductors 82 and 84 that penetrate the printed circuit board 70 in the thickness direction. Via conductor 82 electrically connects the back electrode 80 and the first conductor 10. The connection point between via conductor 82 and the first conductor 10 corresponds to the ground point 12. Via conductor 84 electrically connects the back electrode 80 and the second conductor 20. The connection point between via conductor 84 and the second conductor 20 corresponds to the ground point 22. As a result, ground potential can be supplied to the ground point 12 of the first conductor 10 and the ground point 22 of the second conductor 20. Note that the method for setting the ground potential at ground points 12 and 22 is not particularly limited.

[0063] In this embodiment, a first conductor 10 and a second conductor 20, provided on a printed circuit board 70, are placed on a waveguide 30 provided on a support substrate 32. The first conductor 10 and the second conductor 20 are in contact with the waveguide 30, but are not limited to this. An insulating film may be provided between the first conductor 10 and the second conductor 20 and the waveguide 30, or a gap (specifically, an air layer) may be provided.

[0064] In this embodiment, as shown in Figure 2, the direction of the alternating current flowing through the first conductor 10 and the direction of the current flowing through the second conductor 20 due to the spin wave are both non-orthogonal to the spin wave propagation direction. Specifically, the angle between the direction of the alternating current flowing through the first conductor 10 and the spin wave propagation direction, and the angle between the direction of the current flowing through the second conductor 20 and the spin wave propagation direction are both 45 degrees or less. More specifically, the direction of the alternating current flowing through the first conductor 10 and the direction of the current flowing through the second conductor 20 are parallel to each other and parallel to the spin wave propagation direction.

[0065] When an alternating current flows through the first conductor 10, electromagnetic waves are generated around the first conductor 10 according to Ampere's law. As shown in Figure 2, the electromagnetic waves are strongly radiated and propagated in a direction perpendicular to the direction of the alternating current flowing through the first conductor 10. In this embodiment, since the direction of the alternating current flowing through the first conductor 10 is parallel to the spin wave propagation direction, the propagation direction of the electromagnetic waves generated around the first conductor 10 is perpendicular to the spin wave propagation direction. Therefore, the electromagnetic waves are less likely to be detected by the second conductor 20, and noise for the spin waves can be suppressed.

[0066] Furthermore, in this embodiment, the direction of the current flowing through the second conductor 20 is parallel to the spin wave propagation direction and perpendicular to the electromagnetic wave propagation direction. Therefore, since the current flowing through the second conductor 20 is suppressed by the influence of electromagnetic waves, noise related to spin waves can be further suppressed.

[0067] Furthermore, in this embodiment, the path of the alternating current flowing through the first conductor 10 and the path of the current flowing through the second conductor 20 due to the spin wave are located on the same straight line. Specifically, as shown in Figure 2, the feed point 11 of the first conductor 10, the ground point 12, the ground point 22 of the second conductor 20, and the detection point 21 are located in this order on a hypothetical straight line, the dashed line L. This further suppresses noise related to the spin wave and further improves the accuracy of spin wave detection.

[0068] <Example 2> Figure 4 is a plan view showing the positional relationship between the waveguide 30 and the first conductor 10 and the second conductor 20 of the spin wave device 1B according to Example 2. As shown in Figure 4, in the spin wave device 1B according to Example 2, the direction of the current flowing through the second conductor 20 is different compared to the spin wave device 1A according to Example 1.

[0069] Specifically, the direction of the current flowing through the second conductor 20 is perpendicular to the spin wave propagation direction. In other words, the direction of the current flowing through the second conductor 20 is parallel to the propagation direction of the electromagnetic waves generated around the first conductor 10.

[0070] In this embodiment as well, since the direction of the alternating current flowing through the first conductor 10 is parallel to the spin wave propagation direction, the propagation direction of the electromagnetic waves generated around the first conductor 10 is perpendicular to the spin wave propagation direction. As a result, the electromagnetic waves are less likely to be detected by the second conductor 20, and noise related to the spin waves can be suppressed.

[0071] <Comparative Example> Figure 5 is a plan view showing the positional relationship between the waveguide 30 and the first conductor 10 and the second conductor 20 of the comparative example spin wave device 1x. As shown in Figure 5, in the comparative example spin wave device 1x, the direction of the alternating current flowing through the first conductor 10 is different compared to the spin wave device 1B of Example 2.

[0072] Specifically, the direction of the alternating current flowing through the first conductor 10 is perpendicular to the spin wave propagation direction. Therefore, the propagation direction of the electromagnetic waves generated from the first conductor 10 is parallel to the spin wave propagation direction. Consequently, in the second conductor 20, electromagnetic waves are more easily detected as noise relative to the spin waves.

[0073] [Measurement Results] The following describes the results of measuring the electromagnetic waves and spin waves generated when each of the spin wave devices 1A, 1B, and 1x, as described above, were operated.

[0074] The measurement was performed with the magnetic field source 60 generating a bias magnetic field of 42.5 mT. The direction of the bias magnetic field at this time was parallel to the spin wave propagation direction. A signal generator was used as the AC power supply 40, and an AC current with a frequency of 2.693 GHz and an amplitude of 11.2 mA was applied to the feed point 11 of the first conductor 10. An oscilloscope was used as the voltage measuring instrument 50 to measure the change in voltage at the detection point 21 of the second conductor 20. Figure 6 shows the magnitudes of the electromagnetic waves and spin waves detected by the comparative example and the spin wave devices according to Examples 1 and 2. Specifically, Figure 6 shows the amplitude of the measured voltage, and this amplitude corresponds to the magnitude of the electromagnetic wave and spin wave, respectively.

[0075] Furthermore, electromagnetic waves and spin waves propagate from the first conductor 10 to the second conductor 20 at different speeds. Specifically, because the propagation speed of electromagnetic waves is faster than that of spin waves, electromagnetic waves and spin waves generated by the application of a short-term alternating current can be measured separately.

[0076] On the other hand, when used for measuring brain magnetic fields, it may be necessary to apply alternating current for extended periods. In this case, electromagnetic waves and spin waves may be detected together, resulting in a decrease in the spin wave detection accuracy of the comparative example spin wave device 1x. Specifically, as shown in Figure 6, in the comparative example, electromagnetic waves larger than spin waves were measured.

[0077] In contrast, in the spin wave devices 1A and 1B according to Examples 1 and 2, the direction of electromagnetic wave propagation is not perpendicular to the spin wave propagation direction, so the electromagnetic waves detected by the second conductor 20 are sufficiently suppressed. Specifically, as shown in Figure 6, in both Examples 1 and 2, spin waves larger than the electromagnetic waves were measured. In Example 2, the magnitude of the electromagnetic waves was suppressed to about 7% of the magnitude of the spin waves. In Example 1, the magnitude of the electromagnetic waves was suppressed to about 1% of the magnitude of the spin waves. In other words, the spin wave devices 1A and 1B can suppress noise to the spin waves. This makes it possible to improve the accuracy of spin wave detection.

[0078] (Embodiment 2) Next, Embodiment 2 will be described.

[0079] The main difference in Embodiment 2 compared to Embodiment 1 is the inclusion of a third conductor to which a second alternating current is applied. The following explanation will focus on the differences from Embodiment 1, omitting or simplifying the explanation of the commonalities.

[0080] Figure 7 is a diagram showing the configuration of the spin wave device 100 according to this embodiment. Figure 8 is a plan view showing the positional relationship between the waveguide 30 and the first conductor 10, the second conductor 20, and the third conductor 110 of the spin wave device 100 according to this embodiment.

[0081] As shown in Figure 7, the spin wave device 100 includes a third conductor 110 in addition to the configuration of the spin wave device 1. The spin wave device 100 also includes an AC power supply 140.

[0082] The third conductor 110 excites a spin wave when an alternating current is applied. The third conductor 110 is also called an excitation electrode or excitation antenna. The alternating current applied to the third conductor 110 is an example of a second alternating current, and the spin wave excited by this alternating current is an example of a second spin wave.

[0083] The third conductor 110 includes a feed point 111 to which a second alternating current is applied, and a grounding point 112 connected to ground potential. The second alternating current flows between the feed point 111 and the grounding point 112. The path of the second alternating current can be considered as a straight line connecting the feed point 111 and the grounding point 112. The direction of the second alternating current is parallel to the straight line connecting the feed point 111 and the grounding point 112. The plan view shape of the third conductor 110 is a long rectangle along the x-axis, but is not limited to this. The plan view shape of the third conductor 110 may be a square or a circle.

[0084] In this embodiment, the first conductor 10, the second conductor 20, and the third conductor 110 are arranged in this order on the waveguide 30. That is, the first conductor 10 and the third conductor 110 are arranged with the second conductor 20 in between. The first conductor 10, the second conductor 20, and the third conductor 110 are spaced apart from each other. Note that the third conductor 110 does not have to be in contact with the waveguide 30; for example, it may be provided on an insulating film covering the surface of the waveguide 30. Alternatively, the third conductor 110 may be arranged in a floating state relative to the waveguide 30.

[0085] The third conductor 110 mainly comprises a conductive material such as a metal. For example, the third conductor 110 mainly comprises Au, Ag, Cu, Al, Pt, or C.

[0086] In this embodiment, the waveguide 30 propagates a first spin wave excited in the first conductor 10 and a second spin wave excited in the third conductor 110. Specifically, the waveguide 30 propagates the first spin wave in a first direction from the first conductor 10 to the second conductor 20. This first direction is also referred to as the first spin wave propagation direction. The waveguide 30 also propagates the second spin wave in a second direction from the third conductor 110 to the second conductor 20. This second direction is also referred to as the second spin wave propagation direction. The second spin wave propagation direction is the opposite direction to the first spin wave propagation direction.

[0087] In this embodiment, the direction of the second alternating current flowing through the third conductor 110 and the direction of second spin wave propagation are non-orthogonal. Specifically, the angle between the direction of the second alternating current flowing through the third conductor 110 and the direction of second spin wave propagation is 45 degrees or less. For example, the angle between the direction of the second alternating current flowing through the third conductor 110 and the direction of second spin wave propagation may be 10 degrees or less, or 5 degrees or less, and may be substantially 0 degrees. In other words, the direction of the second alternating current flowing through the third conductor 110 and the direction of second spin wave propagation may be parallel.

[0088] Furthermore, in this embodiment, the path of the first alternating current flowing through the first conductor 10 and the path of the second alternating current flowing through the third conductor 110 are located on the same straight line. Specifically, as shown in Figure 8, the feed point 11 and ground point 12 of the first conductor 10, and the ground point 112 and feed point 111 of the third conductor 110 are located in this order on a hypothetical straight line, the dashed line L. This further suppresses noise on spin waves and further improves the accuracy of spin wave detection.

[0089] In this embodiment, the second conductor 20 is the same as the second conductor 20 of the spin wave device 1B according to Embodiment 1, Example 2. That is, the direction of the current flowing through the second conductor 20 according to this embodiment is orthogonal to the first spin wave propagation direction and the second spin wave propagation direction, respectively. In other words, the direction of the current flowing through the second conductor 20 is parallel to the propagation direction of electromagnetic waves generated around the first conductor 10 and the propagation direction of electromagnetic waves generated around the third conductor 110.

[0090] The second conductor 20 may be the same as the second conductor 20 of the spin wave device 1A according to Embodiment 1 of the first embodiment. That is, the direction of the current flowing through the second conductor 20 according to this embodiment may be parallel to the first spin wave propagation direction and the second spin wave propagation direction, respectively. For example, the feed point 11 and ground point 12 of the first conductor 10, the ground point 22 and detection point 21 of the second conductor 20, and the ground point 112 and feed point 111 of the third conductor 110 may be arranged in this order along a hypothetical straight line, the dashed line L.

[0091] The AC power supply 140 is electrically connected to the feed point 111 of the third conductor 110 and supplies a second AC current from the feed point 111 to the third conductor 110. For example, a signal generator can be used as the AC power supply 140. The frequency of the second AC current is in the GHz band, but is not limited to this. Alternatively, an AC power supply 40 may be electrically connected to the feed point 111 of the third conductor 110 instead of the AC power supply 140.

[0092] When operating the spin wave device 100 according to this embodiment, first, the AC power supply 40 applies a first AC current to the feed point 11 of the first conductor 10, and the AC power supply 140 applies a second AC current to the feed point 111 of the third conductor 110. The application of the first AC current excites the first conductor 10 to a first spin wave. The application of the second AC current excites the third conductor 110 to a second spin wave. At this time, a bias magnetic field is applied to the waveguide 30 by the magnetic field source 60, so the excitation of the first spin wave and the second spin wave can be performed efficiently.

[0093] The excited first spin wave propagates through the waveguide 30 in a first direction from the first conductor 10 to the second conductor 20. The excited second spin wave propagates through the waveguide 30 in a second direction from the third conductor 110 to the second conductor 20. The first and second spin waves propagating through the waveguide 30 interfere with each other, generating an interference wave. The interference wave of the first and second spin waves induces an electromotive force in the second conductor 20, causing a current to flow between the detection point 21 and the ground point 22. As a result, the voltage at the detection point 21 changes, and the voltage change can be detected by the voltage measuring instrument 50. Since the change in voltage at the detection point 21 depends on the physical characteristics of the interference wave, the interference wave can be detected by detecting the change in voltage.

[0094] Interference waves are susceptible to external magnetic fields. Specifically, the wavenumbers of the first spin wave and the second spin wave change due to the external magnetic field. The change in the wavenumbers of the first and second spin waves changes the phase difference between the first and second spin waves at the location where the second conductor 20 is installed. In response to this change in phase difference, the amplitude of the interference wave at the location where the second conductor 20 is installed changes. The change in the amplitude of the interference wave is reflected in the magnitude of the voltage detected by the voltage measuring instrument 50. Therefore, based on the detection results from the voltage measuring instrument 50, the change in the amplitude of the interference wave and the change in the phase difference between the first and second spin waves can be calculated. Based on the change in phase difference, the magnitude of the external magnetic field can be calculated.

[0095] The external magnetic field is the magnetic field (magnetism) to be detected when the spin wave device 100 functions as a magnetic sensor. For example, the external magnetic field is a weak magnetic field generated by living organisms, such as the brain's magnetic field. By having the spin wave device 100 detect the brain's magnetic field, it becomes possible to apply it to BCI (Brain Computer Interface) devices. Alternatively, the spin wave device 100 may be applied to diagnostic devices such as those used to identify the location of epilepsy or brain tumors.

[0096] In addition, methods for detecting signals emitted by the brain include optical methods that use NIRS (Near Infra-Red Spectroscopy) to detect blood flow, and electrical methods that electrically detect brain waves. However, optical methods have the problem of low spatial and temporal resolution, and electrical methods have the problem of low spatial resolution. In contrast, the method of detecting the brain magnetic field using the spin wave device 100 according to this embodiment has high spatial and temporal resolution, so it is possible to realize a system with excellent real-time performance.

[0097] In this embodiment, as shown in Figure 8, the distance D1 between the first conductor 10 and the second conductor 20 is different from the distance D2 between the third conductor 110 and the second conductor 20. Specifically, distance D1 is longer than distance D2. Distance D1 is the shortest distance between the first conductor 10 and the second conductor 20. Distance D2 is the shortest distance between the third conductor 110 and the second conductor 20. Distance D1 may be considered as the distance from the midpoint of the line segment connecting the power supply point 11 and the ground point 12 in the first conductor 10 to the midpoint of the line segment connecting the detection point 21 and the ground point 22 in the second conductor 20. Distance D2 may be considered as the distance from the midpoint of the line segment connecting the power supply point 111 and the ground point 112 in the third conductor 110 to the midpoint of the line segment connecting the detection point 21 and the ground point 22 in the second conductor 20.

[0098] The difference between distances D1 and D2 makes it easier to detect magnetic fields with a small bias magnetic field. When distances D1 and D2 are different, there is a difference in the degree to which the external magnetic field changes the wavenumber of the first spin wave and the degree to which it changes the wavenumber of the second spin wave. Therefore, a phase difference is easily created between the first spin wave and the second spin wave at the position where the second conductor 20 is provided. Consequently, the amplitude of the interference wave also changes more easily, making measurement easier and thus facilitating the detection of the external magnetic field.

[0099] In this embodiment, an example is shown where the first spin wave propagation direction and the second spin wave propagation direction are parallel, but this is not the only example. The first spin wave propagation direction and the second spin wave propagation direction may intersect diagonally or be perpendicular. For example, the plan view shape of the waveguide 30 does not have to be a long rectangle in the x-axis direction, and may have a bent shape at the position where the second conductor 20 is provided. The angle between the first spin wave propagation direction and the second spin wave propagation direction is a right angle or an obtuse angle, but may also be an acute angle. When the angle between the first spin wave propagation direction and the second spin wave propagation direction is an obtuse angle, the distance between the first conductor 10 and the third conductor 110 can be increased, thereby suppressing the influence of electromagnetic waves generated around each of them.

[0100] (Other embodiments) Although one or more embodiments of spin wave devices have been described above based on their respective embodiments, this disclosure is not limited to these embodiments. Without departing from the spirit of this disclosure, various modifications to these embodiments that a person skilled in the art could conceive, as well as configurations constructed by combining components from different embodiments, are also included within the scope of this disclosure.

[0101] For example, the plan view shape of the waveguide 30 does not have to be rectangular; it may be another polygon such as a square. Also, the contour of the plan view shape of the waveguide 30 may include curves; for example, the plan view shape of the waveguide 30 may be circular, elliptical, or a wavy line of a predetermined width.

[0102] Furthermore, for example, the positions of the power supply point 11 and the grounding point 12 in the first conductor 10 may be swapped. The positions of the detection point 21 and the grounding point 22 in the second conductor 20 may be swapped. The positions of the power supply point 111 and the grounding point 112 in the third conductor 110 may be swapped.

[0103] Furthermore, each of the above embodiments can be modified, replaced, added, or omitted in various ways within the scope of the claims or equivalents thereof. [Industrial applicability]

[0104] This disclosure can be used, for example, in magnetic sensors capable of detecting magnetic fields generated by living organisms, such as brain magnetic fields, and in various systems equipped with such magnetic sensors. [Explanation of Symbols]

[0105] 1, 1A, 1B, 100 Spin wave devices 10 First conductor 11, 111 Power supply point 12, 22, 112 Grounding point 20 Second conductor 21 detection points 30 Waveguides 32 Support substrate 40, 140 AC power supply 50 Voltage Measuring Instruments 60 Magnetic field source 70 Printed circuit boards 80 Backside electrode 82, 84 via conductors 110 Third conductor

Claims

1. A first conductor that excites a first spin wave by applying a first alternating current, The second conductor and The device comprises a waveguide that propagates the first spin wave in a first direction from the first conductor to the second conductor, The direction of the first alternating current flowing through the first conductor and the first direction are non-orthogonal. Spin wave device.

2. The angle between the direction of the first alternating current flowing through the first conductor and the first direction is 45 degrees or less. The spin wave device according to claim 1.

3. The waveguide is provided with a magnetic field source for applying a bias magnetic field, The spin wave device according to claim 1.

4. The direction of the bias magnetic field is parallel to the first direction. The spin wave device according to claim 3.

5. The waveguide contains yttrium iron garnet as its main component. The spin wave device according to claim 1.

6. The direction of the current flowing through the second conductor due to the first spin wave and the first direction are non-orthogonal. The spin wave device according to claim 1.

7. The path of the first alternating current flowing through the first conductor and the path of the current flowing through the second conductor by the first spin wave are located on the same straight line. The spin wave device according to claim 6.

8. It comprises a third conductor that excites a second spin wave by applying a second alternating current, The waveguide propagates the second spin wave in a second direction from the third conductor to the second conductor. The first conductor, the second conductor, and the third conductor are arranged in this order. The direction of the second alternating current flowing through the third conductor and the second direction are non-orthogonal. A spin wave device according to any one of claims 1 to 7.

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