Magnetic field measurement method and magnetic field measurement apparatus

Abstract

To provide a magnetic field measurement technique capable of accurately detecting the intensity of a magnetic field and realizing it inexpensively.SOLUTION: Fluorescence emitted from Si vacancies in a SiC crystal (10) when excitation light is irradiated is detected. Then, the intensity of a magnetic field (B⊥) applied to the Si vacancies and perpendicular to a c-axis of the SiC crystal is derived with reference to the intensity of the detected fluorescence.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a magnetic field measuring method and a magnetic field measuring device for measuring a magnetic field. [Background technology]

[0002] Quantum sensing technology that measures environmental conditions (such as temperature and magnetic fields) by reading out the state of electron spin has been put to practical use. Nitrogen Vacancy Centers (NV centers) in diamond crystals are a representative example of quantum sensors.

[0003] For example, when measuring a magnetic field using an NV center, the intensity of the fluorescence emitted by the NV center when irradiated with excitation light is measured while changing the frequency of the microwave applied. The microwave frequency dependence of the fluorescence intensity obtained in this way shows two dips at an interval that depends on the strength of the magnetic field applied to the NV center. Therefore, the strength of the magnetic field applied to the NV center can be derived from the interval between these two dips.

[0004] Non-Patent Document 1 discloses a sensor head incorporating a diamond crystal containing an NV center. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] M.Bahr et al. “Compact All-Optical Quantum Sensor Device Based onNitrogen Vacancy Centers in Diamond”, Phys. Status Solidi A 2023, 220, 2200338 Summary of the Invention [Problem to be solved by the invention]

[0006] In the magnetic field measurement method using the NV center in the diamond crystal, it may be necessary to apply microwaves or a bias magnetic field to the diamond crystal. In this case, in addition to the diamond crystal, a mechanism that functions as a source of microwaves and / or a bias magnetic field must be mounted on the sensor head. Therefore, the structure of the sensor head becomes complicated, and as a result, it becomes difficult to miniaturize the sensor head. Then, for example, it becomes difficult to measure the magnetic field in a narrow space such as inside the human body or inside a pipe. In addition, in the sensor head described in Non-Patent Document 1, in addition to the diamond crystal, a light source (LED) that generates excitation light and a photodetector (PD) that detects fluorescence are built in. In this way, when an element that requires a power supply or an element that outputs an electric signal is built in the sensor head, problems such as vulnerability to electrical noise, low long-term reliability, and high operating costs may occur. In addition, diamond crystals are expensive to begin with. For this reason, it is difficult to implement the magnetic field measurement method using a diamond crystal containing an NV center at low cost.

[0007] One aspect of the present invention has been made in consideration of the above-mentioned problems, and one object of the present invention is to provide a magnetic field measurement technology that can detect the strength of a magnetic field with high accuracy and can be implemented inexpensively. [Means for solving the problem]

[0008] A magnetic field measurement method according to one embodiment of the present invention includes a detection step of detecting fluorescence emitted by Si vacancies in a SiC crystal when irradiated with excitation light, and a derivation step of deriving the intensity of a magnetic field applied to the Si vacancies, the magnetic field being perpendicular to the c-axis of the SiC crystal, by referring to the intensity of the fluorescence detected in the detection step.

[0009] A magnetic field measuring device according to one embodiment of the present invention includes a sensor head incorporating a SiC crystal containing Si vacancies, a light source that emits excitation light, a photodetector that detects fluorescence emitted by the Si vacancies when the excitation light is irradiated, and an optical fiber that guides the excitation light from the light source to the SiC crystal and guides the fluorescence from the SiC crystal to the photodetector. Effect of the Invention

[0010] According to one aspect of the present invention, it is possible to provide a magnetic field measurement technique that can detect the strength of a magnetic field with high accuracy and can be implemented at low cost. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a side view of a SiC crystal. [Diagram 2] 1 is a graph showing the change over time in the intensity of fluorescence emitted from Si vacancies in a SiC crystal when a periodically varying magnetic field is applied while irradiating it with excitation light. [Diagram 3] (a) is a graph showing the relationship between the strength of a magnetic field [mT] perpendicular to the c-axis of a SiC crystal and the intensity of fluorescence [au] emitted by a Si vacancy in the SiC crystal. (b) is a graph showing the relationship between the strength of a magnetic field [mT] parallel to the c-axis of a SiC crystal and the intensity of fluorescence [au] emitted by a Si vacancy in the SiC crystal. [Figure 4] 1 is a flow diagram showing the flow of a magnetic field measuring method according to an embodiment of the present invention. [Diagram 5] 1A is a block diagram showing the configuration of a magnetic field measuring device according to an embodiment of the present invention, while FIG. 1B and FIG. 1C are side views of a SiC crystal built into the sensor head shown in FIG. [Figure 6] 6 is a schematic diagram of various environmental sensors equipped with the magnetic field measuring device shown in Fig. 5. (a) shows a liquid level sensor, (b) shows a rainfall sensor, and (c) shows a rockfall sensor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] (Facts underlying the present invention) First, the facts on which the present invention is based will be described with reference to FIGS.

[0013] 1 is a side view of SiC crystal (silicon carbide crystal) 10. Below, an explanation will be given of SiC crystal 10, which is a 4H—SiC crystal, but the same can be said for 6H—SiC crystal.

[0014] In the present invention, a SiC crystal 10 containing Si vacancies (vacancies resulting from the loss of Si atoms in the SiC crystal 10) is used. The Si vacancies in the SiC crystal 10 function as quantum sensors for detecting a magnetic field, similar to the NV centers in diamond crystals. That is, the Si vacancies in the SiC crystal 10 irradiated with excitation light emit fluorescence. The intensity of the fluorescence is determined according to the intensity of the magnetic field applied to the Si vacancies in the SiC crystal 10. The Si vacancies can be easily formed by simply irradiating the SiC crystal with an electron beam or a particle beam.

[0015] 2 is a graph showing the change over time in the intensity of fluorescence emitted by Si vacancies in SiC crystal 10 when a magnetic field that periodically varies in the range of ±2.5 mT is applied using an electromagnet while irradiating with 26 mW laser light as excitation light. The graph shown in FIG. 2 shows that the intensity of the fluorescence emitted by the Si vacancies is determined according to the intensity (absolute value) of the applied magnetic field. Therefore, it is clear that the intensity of the applied magnetic field can be derived based on the intensity of the fluorescence emitted by the Si vacancies.

[0016] FIG. 3(a) shows the magnetic field B perpendicular to the c-axis of the SiC crystal 10. ⊥ 3 is a graph showing the relationship between the intensity [mT] of the fluorescence emitted by a Si vacancy in the SiC crystal 10 and the intensity [au] of the fluorescence emitted by a Si vacancy in the SiC crystal 10. The graph shown in FIG. 3(a) shows the results of 50 integrated measurements.

[0017] According to the graph shown in FIG. 3(a), in the illustrated measurement range including 0 T, the magnetic field B ⊥ Intensity |B ⊥ Therefore, the magnetic field B ⊥ Intensity |B ⊥In addition, according to the graph shown in FIG. 3(a), in the measurement range of ±1.5 mT centered on 0 T, the magnetic field B ⊥ Intensity |B ⊥ It can be seen that the rate of change in the fluorescence intensity with respect to the magnetic field B ⊥ Intensity |B ⊥ It can be seen that | can be derived with high accuracy.

[0018] It is known that the rate of change of fluorescence intensity with respect to magnetic field strength is about 0.5% per 4 mT (about 0.125% per 1 mT) for NV centers in diamond crystals. Therefore, it can be seen that by using Si vacancies in SiC crystal 10, the strength of a magnetic field can be measured with more than five times the accuracy compared to the case of using NV centers in diamond crystals.

[0019] FIG. 3(b) shows the magnetic field B / / 3 is a graph showing the relationship between the intensity [mT] of the fluorescence emitted by a Si vacancy in the SiC crystal 10 and the intensity [au] of the fluorescence emitted by a Si vacancy in the SiC crystal 10. The graph shown in FIG. 3(b) is the result of 50 integrated measurements.

[0020] According to the graph shown in FIG. 3(b), in the illustrated measurement range including 0 T, the magnetic field B / / Intensity |B / / It can be seen that there is no one-to-one correspondence between the magnetic field | and the intensity of the fluorescence. From this, it can be seen that the magnetic field B / / Instead, the magnetic field B perpendicular to the c-axis of the SiC crystal 10 ⊥ It can be seen that.

[0021] In the graph shown in FIG. 3(b), |B / / The peak in fluorescence intensity that appears near |=1.2 mT is presumed to be due to the level anticrossing between the energy levels of Sz=-3 / 2 and Sz=+1 / 2. / / The peak in fluorescence intensity appearing near |=2.4 mT is presumed to be due to the level anticrossing between the energy levels of Sz=-3 / 2 and Sz=-1 / 2.

[0022] (Magnetic field measurement method) A magnetic field measuring method S1 according to one embodiment of the present invention will be described with reference to FIG.

[0023] FIG. 4(a) is a flow diagram showing the flow of the magnetic field measuring method S1.

[0024] The magnetic field measuring method S1 includes a detection step S11 and a derivation step S12.

[0025] Detection step S11 is a step of detecting fluorescence emitted by Si vacancies in SiC crystal 10 when irradiated with excitation light. The excitation light is, for example, light in a wavelength band including 785 nm, and the fluorescence is, for example, light in a wavelength band including 910 nm. The fluorescence detected in detection step S11 is, for example, light with a wavelength of 900 nm or more and 1000 nm or less that has passed through a long-pass filter, among the fluorescence emitted by Si vacancies in SiC crystal 10. Detection step S11 is performed without applying a bias magnetic field to SiC crystal 10 or without applying microwaves to SiC crystal 10.

[0026] The derivation step S12 is a step of applying a magnetic field B perpendicular to the c-axis of the SiC crystal 10. ⊥ In this step, the intensity of the magnetic field B is calculated by referring to the intensity of the fluorescence detected in the detection step S11. ⊥ The intensity of the magnetic field B and the intensity of the fluorescent light have a one-to-one correspondence (theoretically proportional). Therefore, in the derivation step S12, for example, ⊥ or by using a table showing the correspondence between the intensity of the fluorescence and the magnetic field B⊥ By using a function (e.g., a linear function) to derive the strength of the magnetic field B ⊥ The strength of can be derived.

[0027] As described above, the rate of change in the fluorescence intensity with respect to the strength of the magnetic field is about 0.125% per 1 mT for the NV center in the diamond crystal, whereas it is about 0.5% per 1 mT for the Si vacancy in the SiC crystal 10. Therefore, according to the magnetic field measurement method S1 of this embodiment, ⊥ This makes it possible to measure the strength of the magnetic field with greater accuracy than the magnetic field measurement method using NV centers in diamond crystals.

[0028] Furthermore, the price of the SiC crystal 10 substrate is 1 / 100 or less of the price of the diamond crystal substrate. Therefore, the magnetic field measurement method S1 according to the present embodiment using Si vacancies in the SiC crystal 10 can be implemented more cheaply than a magnetic field measurement method using NV centers in a diamond crystal.

[0029] Furthermore, in the magnetic field measurement method S1 according to this embodiment, it is not necessary to perform a step of applying a bias magnetic field or microwaves to the SiC crystal 10 in the detection step S11. This simplifies the structure of the sensor head (described below), and as a result, it becomes easier to miniaturize the sensor head. This makes it easier to measure the magnetic field in a narrow space, such as inside the human body or inside a pipe.

[0030] (Magnetic field measuring device) A magnetic field measuring device 1 according to one embodiment of the present invention will be described with reference to FIG.

[0031] FIG. 5(a) is a block diagram showing the configuration of the magnetic field measuring device 1.

[0032] The magnetic field measuring device 1 includes a sensor head 11. In this embodiment, in addition to a SiC crystal 10, the sensor head 11 includes a housing 110, a lens 111, an optical window 112, and a mirror 113. The lens 111, the optical window 112, and the mirror 113 are arranged in this order and fixed to the inner surface of the cylindrical housing 110. The SiC crystal 10 is attached to one of the two main surfaces of the optical window 112 that faces the mirror 113.

[0033] The magnetic field measuring device 1 further includes a light source 12 and a photodetector 13. The light source 12 is configured to emit excitation light to be irradiated onto the Si vacancies in the SiC crystal 10. In this embodiment, a laser diode is used as the light source 12. An LED may be used instead of the laser diode. The photodetector 13 is configured to detect fluorescence emitted by the Si vacancies in the SiC crystal 10 when irradiated with excitation light. In this embodiment, a photodiode is used as the photodetector 13.

[0034] The magnetic field measuring device 1 further includes an optical fiber 14 and a spatial optical system 15. The optical fiber 14 and the spatial optical system 15 are configured to guide the excitation light emitted from the light source 12 to the SiC crystal 10, and also to guide the excitation light emitted from the SiC crystal 10 to the photodetector 13. In this embodiment, the optical fiber 14 is a multimode fiber. The spatial optical system 15 is configured with a collimator lens 151, a dichroic mirror 152, and an isolator 153.

[0035] An isolator 153 is disposed on the optical path of the excitation light emitted from the light source 12, and a dichroic mirror 152 is disposed on the optical path of the excitation light transmitted through the isolator 153. The dichroic mirror 152 is configured to reflect the excitation light and transmit the fluorescence, and reflects the excitation light transmitted through the isolator 153 and rotates the traveling direction of the excitation light by 90°. A collimating lens 151 is disposed on the optical path of the excitation light reflected by the dichroic mirror 152. The collimating lens 151 converts the light beam of the excitation light from a parallel light beam to a convergent light beam. One end 14a of the optical fiber 14 is disposed on the optical path of the excitation light transmitted through the collimating lens 151. The optical fiber 14 guides the excitation light transmitted through the collimating lens 151 to the sensor head 11. The excitation light emitted from the other end 14b of the optical fiber 14 is collected by the lens 111, passes through the optical window 112, and enters the SiC crystal 10.

[0036] On the other hand, the fluorescence emitted from the SiC crystal 10 passes through the optical window 112, either directly or after being reflected by the mirror 113, and is collected by the lens 111. The fluorescence collected by the lens 111 is incident on the end 14b of the optical fiber 14 described above. The optical fiber 14 guides the fluorescence collected by the lens 111 to the spatial optical system 15. The fluorescence emitted from the end 14a of the optical fiber 14 is incident on the collimating lens 151 described above. The collimating lens 151 converts the fluorescent light beam from a diverging light beam to a parallel light beam. The fluorescence that has passed through the collimating lens 151 is incident on the dichroic mirror 152 described above. The dichroic mirror 152 transmits the fluorescence that has passed through the collimating lens 151. The fluorescence that has passed through the dichroic mirror 152 is incident on the photodetector 13. The above-mentioned isolator 153 is a component for preventing the oscillation state of the light source 12 from changing due to the excitation light reflected by the lens 111 or the end 14b of the optical fiber 14 being incident on the light source 12. When a light source 12 with a highly stable oscillation state is used, the isolator 153 may be omitted.

[0037] The magnetic field measuring device 1 further includes a processor 16 and a transimpedance amplifier 17. The above-mentioned photodetector 13 is connected via the transimpedance amplifier 17 to an electronic computer (for example, a personal computer) having the processor 16 built therein.

[0038] The photodetector 13 generates an electrical signal that represents the intensity of the fluorescence transmitted through the dichroic mirror 152. The transimpedance amplifier 17 converts the electrical signal generated by the photodetector 13 from a current signal to a voltage signal. The processor 16 calculates the magnetic field B perpendicular to the c-axis of the SiC crystal 10. ⊥ The intensity of the magnetic field B perpendicular to the c-axis of the SiC crystal 10 is calculated by referring to the electrical signal obtained from the photodetector 13 via the transimpedance amplifier 17. As described above, the intensity of the electrical signal generated by the photodetector 13 represents the intensity of the fluorescent light transmitted through the dichroic mirror 152, i.e., the intensity of the fluorescent light emitted by the Si vacancies in the SiC crystal 10 when irradiated with the excitation light. ⊥ The intensity of is derived with reference to the intensity of the fluorescence emitted by Si vacancies in the SiC crystal 10 when irradiated with excitation light.

[0039] As described above, the rate of change in the fluorescence intensity with respect to the strength of the magnetic field is about 0.125% per 1 mT for the NV center in the diamond crystal, whereas it is about 0.5% per 1 mT for the Si vacancy in the SiC crystal 10. Therefore, according to the magnetic field measuring device 1 of this embodiment, ⊥ This makes it possible to measure the strength of the magnetic field with greater accuracy than with a magnetic field measurement device that uses NV centers in diamond crystals.

[0040] Furthermore, the price of the SiC crystal 10 substrate is 1 / 100 or less of the price of the diamond crystal substrate. Therefore, the magnetic field measurement device 1 according to this embodiment using Si vacancies in the SiC crystal 10 can be manufactured more cheaply than a magnetic field measurement device using NV centers in a diamond crystal.

[0041] Furthermore, in the magnetic field measuring device 1 according to this embodiment, there is no need to incorporate into the sensor head 11 a mechanism for applying a bias magnetic field or microwaves to the SiC crystal 10. This simplifies the structure of the sensor head 11, and as a result, makes it easier to miniaturize the sensor head 11. This makes it easier to measure the magnetic field in a narrow space, such as inside the human body or inside a pipe.

[0042] In the sensor head 11, the SiC crystal 10 may be arranged so that the c-axis is parallel to the axis of the housing 110 (the direction of travel of the excitation light and the fluorescent light), as shown in (b) of FIG. 5. In this case, the magnetic field measuring device 1 is used to measure the B ⊥ In the sensor head 11, the SiC crystal 10 may be arranged so that the c-axis is perpendicular to the axis of the housing 110 (the direction of travel of the excitation light and the fluorescence) as shown in FIG. 5(c). In this case, the magnetic field measuring device 1 is used to measure the B ⊥ The intensity of the light can be measured.

[0043] Moreover, in the magnetic field measuring device 1 according to this embodiment, the light source 12 and the photodetector 13 are disposed outside the sensor head 11 by adopting a configuration in which the excitation light and the fluorescence are transmitted using the optical fiber 14 and the spatial optical system 15. Therefore, in the magnetic field measuring device 1 according to this embodiment, it is not necessary to incorporate elements that require a power supply or elements that output electric signals into the sensor head 11. Therefore, it is possible to realize a magnetic field measuring device 1 that is resistant to electrical noise, has high long-term reliability, and has low operating costs.

[0044] In addition, in the magnetic field measuring device 1 according to this embodiment, the structure of the sensor head 11 can be further simplified by omitting the lens 111 incorporated in the sensor head 11. In this case, for example, by providing a GRIN lens at the end 14b of the optical fiber 14, it is possible to obtain optical performance similar to that in the case where the lens 111 is incorporated in the sensor head 11.

[0045] The structure of the magnetic field measuring device 1 according to this embodiment can also be applied to a measuring device using any quantum sensor, such as an NV center in a diamond crystal. When applied to a measuring device using an NV center in a diamond crystal, the SiC crystal 10 containing Si vacancies in the magnetic field measuring device 1 can be replaced with a diamond crystal containing an NV center. Even in this case, the following effects are achieved: (1) quantum measurement in a narrow space, such as inside the human body or inside a pipe, becomes easy; and (2) quantum measurement that is resistant to electrical noise, has high long-term reliability, and has low operating costs becomes possible.

[0046] (Application example of magnetic field measuring device) An application example of the above-mentioned magnetic field measuring device 1 will be described with reference to FIG.

[0047] FIG. 6(a) is a schematic diagram of a liquid level sensor 2 including a magnetic field measuring device 1. FIG.

[0048] In addition to the magnetic field measuring device 1, the liquid level sensor 2 includes a cylindrical housing 20 with a part of the top plate and a part of the bottom plate open, and a float 21 that floats on the liquid that has entered the inside of the housing 20 from the opening of the bottom plate. The sensor head 11 of the magnetic field measuring device 1 is fixed to the top plate of the housing 20, and a magnet M is built into the float 21. When the liquid level rises or falls, the distance between the sensor head 11 and the magnet M changes, and the strength of the magnetic field applied to the SiC crystal 10 in the sensor head 11 changes. Therefore, if the strength of this magnetic field is measured by the magnetic field measuring device 1, it is possible to estimate the height of the liquid level from the measurement result.

[0049] FIG. 6(b) is a schematic diagram of a rain sensor 3 including the magnetic field measuring device 1.

[0050] In addition to the magnetic field measuring device 1, the rain sensor 3 includes a cylindrical housing 30 with a portion of the top plate open, a tipping bucket 32, and a funnel 31 that guides rainwater that has entered the inside of the housing 30 from the opening in the top plate to the tipping bucket 32. The sensor head 11 of the magnetic field measuring device 1 is fixed to the bottom plate of the housing 30, and a magnet M is attached to the underside of the tipping bucket 32. When rainwater accumulates and the tipping bucket 32 ​​tilts, the distance between the sensor head 11 and the magnet M changes, and the strength of the magnetic field applied to the SiC crystal 10 in the sensor head 11 changes. Therefore, if the strength of this magnetic field is measured by the magnetic field measuring device 1, it is possible to estimate the amount of rainwater from the measurement results.

[0051] FIG. 6(c) is a schematic diagram of a rockfall sensor 4 including the magnetic field measuring device 1.

[0052] In addition to the magnetic field measuring device 1, the rockfall sensor 4 includes a cylindrical housing 40 with one end open, and a wire 41. The sensor head 11 of the magnetic field measuring device 1 is fixed to a side plate of the housing 40, and a magnet M housed inside the housing 40 is connected to the wire 41. When a falling rock comes into contact with the wire 41 and the magnet M housed in the housing 40 is attracted to the wire 41 and moves, the distance between the sensor head 11 and the magnet M changes, and the strength of the magnetic field applied to the SiC crystal 10 in the sensor head 11 changes. Therefore, if the strength of this magnetic field is measured by the magnetic field measuring device 1, the presence or absence of a rockfall can be estimated from the measurement result.

[0053] In this way, the magnetic field measuring device 1 is configured to have a small sensor head 11 at the tip of the optical fiber 14, and can be suitably used for various environmental sensors that measure remote environments, particularly high temperature environments and outdoor environments, such as the liquid level sensor 2, the rainfall sensor 3, and the rockfall sensor 4. The magnetic field measuring device 1 is suitable for high temperature and outdoor environments because it does not require the sensor head 11 to be equipped with components that are prone to failure in these environments.

[0054] (summary) The magnetic field measurement method according to aspect 1 of the present invention includes a detection step of detecting fluorescence emitted from Si vacancies in a SiC crystal when irradiated with excitation light, and a derivation step of deriving the intensity of a magnetic field applied to the Si vacancies, the magnetic field being perpendicular to the c-axis of the SiC crystal, by referring to the intensity of the fluorescence detected in the detection step.

[0055] A magnetic field measurement method according to a second aspect of the present invention is the magnetic field measurement method according to the first aspect, wherein the measurement range of the magnetic field strength includes 0T, and the rate of change of the fluorescence intensity with respect to the magnetic field strength in the measurement range is 0.5% or more per 1 mT.

[0056] A magnetic field measuring method according to a third aspect of the present invention is the magnetic field measuring method according to the first or second aspect, wherein the detection step is carried out without applying a bias magnetic field to the SiC crystal.

[0057] A magnetic field measuring method according to a fourth aspect of the present invention is the magnetic field measuring method according to any one of the above first to third aspects, wherein the detection step is carried out without applying microwaves to the SiC crystal.

[0058] A magnetic field measuring method according to aspect 5 of the present invention is a magnetic field measuring method according to any one of aspects 1 to 4 above, in which, in the detection step, an optical fiber is used to guide the excitation light from a light source to the SiC crystal, and to guide the fluorescence from the SiC crystal to a photodetector.

[0059] A magnetic field measuring device according to a sixth aspect of the present invention includes a sensor head incorporating a SiC crystal containing Si vacancies, a light source that emits excitation light, a photodetector that detects fluorescence emitted by the Si vacancies when the excitation light is irradiated, and an optical fiber that guides the excitation light from the light source to the SiC crystal and guides the fluorescence from the SiC crystal to the photodetector.

[0060] A magnetic field measuring device according to a seventh aspect of the present invention is the magnetic field measuring device according to the sixth aspect, further comprising a processor that derives the intensity of the magnetic field applied to the Si vacancies, the magnetic field being perpendicular to the c-axis of the SiC crystal, by referring to the intensity of the fluorescence detected by the photodetector.

[0061] (Additional Note 1) In the above-mentioned embodiment, the measurement of the magnetic field perpendicular to the c-axis of the SiC crystal has been described. This is because the strength of the magnetic field perpendicular to the c-axis of the SiC crystal corresponds one-to-one to the intensity of the fluorescence emitted by the Si vacancy. However, the magnetic field whose strength corresponds one-to-one to the intensity of the fluorescence emitted by the Si vacancy is not limited to the magnetic field perpendicular to the c-axis of the SiC crystal. If the magnetic field whose strength corresponds one-to-one to the intensity of the fluorescence emitted by the Si vacancy is set so that the change in the fluorescence intensity due to the level anti-crossing can be ignored, the magnetic field measurement method and the magnetic field measurement device according to the present invention can be used as the measurement target even if the magnetic field is not perpendicular to the c-axis of the SiC crystal.

[0062] (Additional Note 2) The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in the above-described embodiments are also included in the technical scope of the present invention. [Explanation of symbols]

[0063] 10 SiC crystal S1 Magnetic field measurement method S11 Detection process S12 Derivation process 1 Magnetic field measuring device 11 Sensor head 12 light source 13 Photodetector 14 Optical Fiber 15 Spatial optical system 16 processors 17 Transimpedance Amplifier

Claims

1. a detection step of detecting fluorescence emitted from Si vacancies in the SiC crystal when irradiated with excitation light; A magnetic field applied to the Si vacancies, the magnetic field being perpendicular to the c-axis of the SiC crystal, is derived by referring to the intensity of the fluorescence detected in the detection step. Magnetic field measurement method.

2. The measurement range of the magnetic field strength includes 0 T, A rate of change in the intensity of the fluorescence relative to the intensity of the magnetic field in the measurement range is 0.5% or more per 1 mT. The magnetic field measuring method according to claim 1 .

3. The detecting step is performed without applying a bias magnetic field to the SiC crystal. The magnetic field measuring method according to claim 1 or 2.

4. The detection step is carried out without applying microwaves to the SiC crystal. The magnetic field measuring method according to claim 1 or 2.

5. In the detection step, an optical fiber is used to guide the excitation light from a light source to the SiC crystal and guide the fluorescence from the SiC crystal to a photodetector. The magnetic field measuring method according to claim 1 or 2.

6. A sensor head having a built-in SiC crystal containing Si vacancies; A light source that emits excitation light; a photodetector for detecting fluorescence emitted by the Si vacancies when irradiated with the excitation light; an optical fiber that guides the excitation light from the light source to the SiC crystal and guides the fluorescent light from the SiC crystal to the photodetector. Magnetic field measuring device.

7. The magnetic field applied to the Si vacancies is perpendicular to the c-axis of the SiC crystal. The magnetic field is applied to the Si vacancies ... applied to the SiC crystal. The magnetic field is applied to the SiC crystal. The magnetic field measuring device according to claim 6.

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