JPH0442077A - Measuring method for magnetic field - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for detecting weak magnetic fields.

[Prior Art] Measurement of a magnetic field is one of the most basic measurements in measuring the magnetic properties of substances, and is very important.

Conventionally, known methods for measuring magnetic fields include using a Hall element that utilizes the Hall effect of a semiconductor, or a magnetoresistive element that utilizes the magnetoresistive effect of a semiconductor or magnetic material as a sensor. The measurement range when using the element is on the order of several glass to several tens of kilogauss.

A method for measuring weak magnetic fields is to use a flux gate with a detection winding wound around a magnetic core such as permalloy as a sensor, and to measure the change in the output of the detection winding that occurs when the magnetic field to be measured is applied to the flux gate. A method of measuring magnetic fields from

In addition, magnetic fields can be measured with high sensitivity by using magnetic field sensors that utilize nuclear magnetic resonance (NMR), sensors that utilize electron spin resonance (ESR), or by utilizing the coherence of magnetic fields due to the Josephson effect. Superconducting quantum interferometer [called SQUID]. ] is also known. Using the SQUID, it is possible to measure magnetic flux densities as small as about 10-9 Gauss.

[Problems to be Solved by the Invention] A magnetic sensor using the Hall effect has a problem in that it is difficult to measure a weak magnetic field.

Fluxgate and NMR capable of measuring weak magnetic fields
, ESR, or SQUID have a complicated structure and are difficult to manufacture, which not only makes them extremely expensive, but also makes them difficult to handle.

An object of the present invention is to propose a magnetic field detection method that can measure weak magnetic fields using a sensor with a simple structure.

[Means for Solving the Problems] The measuring method of the present invention is characterized in that when a magnetic field is applied to a junction between a superconductor and a permanent conductive metal while a current is flowing through the junction, The strength or direction of the magnetic field is detected by using the phenomenon that the resistance value changes depending on the strength of the magnetic field.

In the measurement method of the present invention, a common electrode made of a normal conductor metal, a current electrode, and a voltage electrode are bonded to a base made of a superconductor, and at least the surface provided with the common electrode is made a flat magnetic sensing surface. A means for flowing a constant current through the common electrode and the current electrode using a sensor, and a voltage detection means for detecting the voltage generated between the common electrode and the voltage electrode while the constant current is flowing as a magnetic detection voltage are provided. . Then, while keeping the temperature of the sensor below the critical temperature of the superconductor, the maximum and minimum values of the magnetic detection voltage are determined by changing the attitude of the sensor in the magnetic field to be measured. Find the strength of the magnetic field to be measured from the difference from the minimum value.

The process of changing the attitude of the sensor to obtain the minimum and maximum values of the magnetic detection voltage can be performed, for example, by rotating the sensor in the following steps. That is, the rotation center axis of the sensor is determined in advance, and the sensor is first rotated around an arbitrary first axis in the magnetic field to be measured to find the position where the magnetic detection voltage is maximum. Next, the sensor is rotated about a second axis perpendicular to the magnetic sensing surface of the sensor at the position where the magnetic sensing voltage is at its maximum, and the minimum and maximum values of the magnetic sensing voltage are determined.

In addition, when determining the direction of the magnetic field to be measured, if the position of the sensor is changed in the magnetic field to be measured and the position where the magnetic detection voltage is minimum is determined as the minimum detection voltage position, the magnetic sensing at the minimum detection voltage position is determined. The direction perpendicular to the plane is the direction of the magnetic field to be measured.

In this case, the minimum detected voltage position can be determined by rotating the sensor in the following procedure.

That is, the rotation center axis of the sensor is determined in advance, and the sensor is first rotated around the first axis in the magnetic field to be measured, and the position where the magnetic detection voltage is maximum is determined as the reference position. Next, the sensor is rotated around a second axis perpendicular to the magnetic sensing surface of the sensor at this reference position, and the position where the magnetic detection voltage is minimum is defined as the minimum detection voltage position.

The direction of the magnetic field to be measured can also be determined by the following method.

The rotation center axis of the sensor is determined in advance, and the sensor is first rotated around the first axis in the magnetic field to be measured, and the position where the magnetic detection voltage is maximum is determined as the reference position. Next, a second position perpendicular to the magnetic sensing surface of the sensor at this reference position
The position where the magnetic detection voltage is maximum is determined as the maximum detection voltage position by rotating the sensor around the axis of The direction along the line of intersection with the second plane along the surface is defined as the direction of the magnetic field.

The metal may be any metal that can be bonded to the superconductor without completely impairing the properties of the superconductor, and can be selected from the metal group consisting of gold, silver, platinum, and alloys thereof, for example.

The above-mentioned superconductor has a large critical current density and a sufficiently large Meissner effect, such as YBa2Cu3O.
Buta, Bi2 Sr2 Ca2 Cu3Oy.

(Bil-xPbx)2 Sr2 Ca2 Cu3O.
Ceramics or thin films such as -1 or TJ22 Ba2 Ca2 Cu3O1 can be used.

[Function] The present inventor has confirmed that when a magnetic field is applied to the junction between a superconductor and a normal conductor metal, the resistance of the junction changes depending on the magnetic field. This is because when magnetic lines of force enter a thin region at the interface between a superconductor and a permanent conductive metal (a region as thick as the magnetic field penetration depth), the current flowing through the junction becomes less than the critical current. Even if there is, superconductivity is locally lost and resistance appears in the superconductor near the junction.

When a magnetic field is applied perpendicularly to the magnetic sensing surface of the sensor, the magnetic field is concentrated at the end of the base around the magnetic sensing surface due to the Meissner effect. At this time, the magnetic lines of force are repelled on the magnetic sensing surface, and the junction between the common electrode and the superconductor is not affected by the magnetic field. In this state, the resistance of the joint of the common electrode is only the resistance generated based on the resistance of the normal conductor metal.

In order to detect with high sensitivity the change in resistance of the common electrode junction when a magnetic field is applied, it is preferable to keep the resistance of this junction as low as possible.

When the voltage between the common electrode and the voltage electrode is detected as a magnetic detection voltage while a constant current is flowing through the common electrode and the current electrode, the magnetic detection voltage is generated in the direction in which the magnetic sensing surface of the sensor is perpendicular to the direction of the magnetic field. It is at its minimum when the magnetic field is in the direction of the magnetic field, and it is at its maximum when the magnetic sensing surface is parallel to the direction of the magnetic field.

Therefore, the strength of the magnetic field to be measured can be determined by changing the orientation of the sensor, determining the maximum and minimum values of the magnetic detection voltage, and taking the difference between the maximum and minimum values of the magnetic detection voltage. .

Further, the position where the magnetic detection voltage is minimum can be determined as the minimum detection voltage position, and the direction perpendicular to the magnetic sensing surface at the minimum detection voltage position can be detected as the direction of the magnetic field to be measured.

Furthermore, if the center axis of rotation of the sensor is determined in advance and the position where the magnetic detection voltage is maximum when the sensor is rotated around an arbitrary first axis in the magnetic field to be measured is set as the reference position, then at this reference position, The magnetic sensing surface is aligned with the direction of the magnetic field. However, in this state, it is only known that the magnetic field lines are on the same plane as the magnetic sensing surface, but the direction of the magnetic field is not yet known. Next, rotate the sensor around a second axis perpendicular to the magnetic sensing surface of the sensor at the reference position,
When the position where the magnetic detection voltage is minimum is found, this position becomes the minimum detection voltage position, and the direction perpendicular to the magnetic sensing surface at this position coincides with the direction of the magnetic field.

Furthermore, if the sensor is rotated around the second axis and the position where the magnetic detection voltage is maximum is determined as the maximum detection voltage position, the lines of magnetic force will also be on the same plane as the magnetic sensing surface at this maximum detection voltage position. It turns out that there is. Therefore, the plane along the magnetic sensing surface of the sensor at the reference position is defined as the first plane, and the plane along the magnetic sensing surface of the sensor at the maximum detection voltage position is defined as the second plane, and the intersection line of these first and second planes When , the direction along the intersection line coincides with the direction of the magnetic field.

[Example] The present invention will be described in detail below with reference to the accompanying drawings.

Figure 1 shows an example of the configuration of the sensor used in the present invention. In the figure, 1 is a base made of an oxide superconductor or a metallic superconductor, and Ql is a normal conductor metal bonded to the base 1. The common electrodes q2 and q3 thus formed are a current electrode and a voltage electrode, respectively, which are similarly formed by bonding a normal conductor metal to the base 1. In this example, the substrate 1
is formed into a rectangular plate shape, the electrodes q1 to q3 are arranged in a straight line on one main surface of the base 1, and the current electrode q2 and the voltage electrode q3 are arranged at a predetermined interval. has been done. In this specification, the surface on which the common electrode q1 exists is referred to as a magnetic sensing surface 1a.

The above-mentioned superconductor substrate 1 and metal electrodes q1 to q
3 can be bonded by ultrasonic bonding or spot welding.

In the ultrasonic bonding method, the base 1 and the electrode Ql are bonded using a known ultrasonic welding device or a device based on the same principle.
- It can be carried out by applying ultrasonic waves to the contact part with Q3. When ultrasonic waves are applied to the contact areas between the base body 1 and the electrodes q1 to q3, the surface of the base body 1 made of a superconductor is cleaned, and each electrode is bonded to the base body 1 by the pressing force of the ultrasonic power. Ru. In the experiment, an ultrasonic wire bonding device used to bond wires to electrodes of semiconductor ICs was used to bond a substrate 1 made of an oxide superconductor and electrodes q1 to 1 made of a normal conductor metal.
It was possible to form a good joint with q3.

Further, the spot welding method can also be carried out using a known spot welding device. In the case of spot welding, electrodes q1 to q3 are brought into contact with the base 1, each electrode is pressurized against the base 1, and a pulsed current is passed through each electrode and the base. Thereby, each electrode can be joined to the base 1 by generating heat at the contact portion between each electrode and the base.

The common electrode q1 of this embodiment is formed by joining the middle point of a silver wire L1 of a predetermined length to the base 1, and both ends of the silver wire L1 are connected to a constant current power supply terminal a and a voltage detection means terminal, respectively. connected to.

Further, the other electrodes q2 and q3 are formed by joining one ends of silver wires L2 and L3 of a predetermined length to the base body 1, respectively, and the other ends of these silver wires L2 and L3 are connected to constant current power supply terminal a, respectively. ' and the terminal for voltage detection means -.

In the embodiment, silver wire was used as the metal constituting the electrodes q1 to q3, but other permanent conductive metals such as gold, platinum, or alloys thereof may also be used.

Is it preferable to use a noble metal with low resistance as the metal constituting the electrodes q1 to q3, or is the normal conductor metal used in the present invention a metal that does not completely impair the characteristics of the superconductor when bonded to the superconductor? Any metal other than noble metals may be used.

In the magnetic field measurement method of the present invention, the sensor 2 as described above is used, and a constant current source 3 (means for flowing a constant current through the common electrode and the current electrode) is provided between the common electrode q1 and the current electrode q2 of this sensor. , and a voltmeter 4 (voltage detection means) is connected between the common electrode q1 and the voltage electrode q3. The current flowing between the common electrode ql and the current electrode q2 through the constant current source 3 is set to be smaller than the critical current value of the superconductor forming the base 1 by a predetermined value.

As shown in FIG. 2, when a magnetic field H in a direction perpendicular to the magnetic sensing surface 1a of the sensor 2 is applied, the lines of magnetic force are excluded from the magnetic sensing surface 1a of the base 1 due to the Meissner effect, and lines of magnetic force are created at both ends of the base 1. concentrate.

In this state, since the common electrode q1 and the current electrode q2 are not affected by the magnetic field, the superconductivity of the base 1 is not lost even if a current is passed through the common electrode q1 and the current electrode q2.

The voltage between the common electrode q1 and the voltage electrode 4 at this time is
There is only a voltage drop due to the resistance of the normal conductor metal that constitutes the common electrode q1.

Next, when the sensor base 1 is rotated so that the direction along the magnetic sensing surface 1a matches the direction of the magnetic field H as shown in FIG. 3, the lines of magnetic force come into contact with the magnetic sensing surface 1a. In this state, the voltage detected by the voltage detection means 4 changes depending on the strength of the magnetic field.

This seems to be due to the following reasons. That is, when the lines of magnetic force come into contact with the magnetic sensing surface 1a, the magnetic sensing surface 1a
Magnetic field lines penetrate from an extremely thin layer (magnetic field penetration length λ, approximately) near the surface of the magnetic field. electrode ql.

Since a current relatively close to the critical current flows from the constant current source 3 near the junction of q2, when the magnetic field lines enter the surface layer of the magnetic sensing surface, the superconductivity near the junction locally increases. The resistance value of the part where superconductivity is lost increases. In this state, the voltage between the common electrode q1 and the voltage electrode q3 increases by the amount that the resistance value of the joint of the common electrode q1 increases, and the voltage detected by the voltage detection means 4 increases.

In the above explanation, the extreme cases where the magnetic sensing surface 1a of the sensor is perpendicular to the magnetic field and the extreme case where it is parallel to the magnetic field are described, but as is clear from the experiment described later, in reality, the magnetic sensing surface 1a The voltage detected by the voltage detection means 4 changes depending on the angle θ between the magnetic field H and the magnetic field H. Therefore, by detecting this detection voltage as the magnetic detection voltage E, the magnetic field can be detected.

The current I flowing from the constant current source 3 through the common electrode q1 and the current electrode q2 is set to an appropriate value in consideration of the critical current of the superconductor constituting the base 1 and the ambient temperature (below the critical temperature). The detection sensitivity of the magnetic field can be adjusted depending on the ambient temperature and/or the magnitude of the current I.

In the example, first, 3 calcined powders of YBa2Cu3O7-a were
Press molded with a pressure of [jon/cm2] to a thickness of 1
．． A disc-shaped pellet with a diameter of 5 [mm] and a diameter of 14 [mm] was produced. This pellet was placed in a furnace in an oxygen atmosphere and fired through the temperature process shown in FIG. 4 to produce an oxide superconductor with a critical temperature of 93 (l 2 ).

The bulk of this oxide superconductor is 1.5x! , 5 ×1
A substrate 1 was formed by cutting into 2 mm strips, and electrodes q1 to q3 were formed on the surface of the substrate 1 by ultrasonic bonding using a silver wire with a diameter of 50 μm.

The area of electrode ql ~Q:l is 3. ΩX 10-4 [cm
It was 21. After electrode formation, heat treatment was performed at 500° C. for 1 hour.

The sensor 2 manufactured by the above method is cooled with liquid nitrogen, the sensor 2 is maintained at various temperatures T, and the common electrode q1 is
Constant current 1 [mA] passed through and current electrode q2
The relationship between the magnetic detection voltage E [mV] obtained between the common electrode q1 and the voltage electrode q3 was measured. The results are shown in FIG. In FIG. 5, the parameter T=11 and -100K indicate the temperature of the sensor. When the temperature of the sensor is higher than the critical temperature (93K), the relationship between the current ■ and the magnetic detection voltage E is linear; when the temperature of the sensor is lower than the critical temperature, the relationship between the current ■ and the voltage E is linear. The relationship becomes nonlinear. In order to measure the magnetic field, it is necessary to keep the temperature of the sensor 2 below a critical temperature and to make the current vs. voltage E characteristic nonlinear.

Next, with the current ■ constant (=100 mA) and the angle of incidence θ of the magnetic field H on the magnetic sensing surface 1a as a parameter, we calculated the relationship between the magnetic detection voltage E [mV3] and the magnetic field H [Gaus+], as shown in Figure 6. The results shown are obtained.

From this result, when the incident angle θ is 90 degrees, the magnetic field H is reduced to 0.
The magnetic detection voltage E does not change at all even if it is changed in the range of ~ several Gauss. When the incident angle θ is 0 degrees, the magnetic detection voltage E changes greatly even if a relatively weak magnetic field is applied. When the incident angle θ is 45 degrees, the magnetic detection voltage takes an intermediate value between 90 degrees and 0 degrees.

The measuring method of the present invention utilizes the above characteristics of the sensor 2 to measure the strength (absolute value) of the magnetic field and the direction of the magnetic field.

When measuring the strength of the magnetic field, the common electrode q of sensor 2
1 and current electrode q2, a constant current source 3 is connected to the common electrode q
A voltage detection means 4 is connected between the voltage electrode q3 and the voltage electrode q3.

The temperature of the sensor 2 is then maintained below the critical temperature of the superconductor. Then, the attitude of the sensor 2 is changed in the magnetic field H to be measured, the maximum value and the minimum value of the magnetic detection voltage E are determined, and the difference between the maximum value and the minimum value of the magnetic detection voltage E is determined. The value of this difference corresponds to the strength of the magnetic field to be measured when the incident angle θ is 90 degrees. The relationship between the value of this difference and the strength of the magnetic field is determined through experiments (thereby, the strength of the magnetic field can be detected).

In addition, if the position of the sensor 2 is changed in the magnetic field to be measured and the position where the magnetic detection voltage is minimum is determined as the minimum detection voltage position, the direction perpendicular to the magnetic sensing surface at the minimum detection voltage position is the magnetic field to be measured H It can be detected as the direction of

In order to obtain the minimum value and maximum value of the magnetic detection voltage, for example, the attitude of the sensor may be changed in the following procedure.

First, the rotation center axis of the sensor 2 is determined. For example, as shown in FIG. 7, the origin 0 is the midpoint between the common electrode q1 and the voltage electrode q3, and the straight line A-A- connecting the common electrode q1 and the voltage electrode q3 is connected to the magnetic sensing surface 1a of the sensor 2. A straight line BB' that is perpendicular to the above and passes through the origin O is determined as the rotation center axis of the sensor 2.

First, the sensor 2 is rotated in a magnetic field H with the rotation center axis B-B'' of the sensor 2 set in an arbitrary direction in the direction of a first axis.In this example, as shown in FIG.
Using an orthogonal coordinate system of y and x, the origin O of the sensor 2 is taken as the origin of the coordinates, and the Z axis perpendicular to the plane of the figure is taken as the first axis. This first axis and the rotation center axis B-B- of the sensor 2
With these values matched, the sensor 2 is rotated around the central axis of rotation, and the position where the magnetic detection voltage E is maximized is determined as the reference position. The sensor 2 shown by the solid line in FIG. 8 is in this reference position, and in this state the magnetic sensing surface 1a of the sensor 2 is
is parallel to the direction of the magnetic field H. However, in this state,
It is only known that the lines of magnetic force are on the same plane as the magnetic sensing surface 1a, but the direction of the magnetic field is not known.

Therefore, next, a straight line C-C- perpendicular to the magnetic sensing surface of the sensor at the reference position is determined as the second axis, and the rotation center axis B-B- of the sensor is directed in the direction of this second axis C-C-. to rotate the sensor.

During the rotation of this sensor, the minimum and maximum values of the magnetic detection voltage E are determined. In this way, move the sensor along the second axis C-C.
The position where the magnetic detection voltage E becomes maximum when rotated around - is called the detection voltage maximum position, and the position where the magnetic detection voltage E becomes the minimum is called the detection voltage minimum position.

The strength of the magnetic field to be measured can be determined from the difference between the magnetic detection voltages at the maximum detection voltage position and the minimum detection voltage position. Further, the direction perpendicular to the magnetic sensing surface 1a at the minimum detection voltage position is the direction of the magnetic field H.

Furthermore, when the sensor 2 is at the reference position shown by the solid line in FIG.
along the magnetic sensing surface 1a of the sensor at the maximum detection voltage position (also parallel to the lines of magnetic force), which is determined with the rotation center axis of the sensor oriented in the direction of the second axis C-C-.
If the line of intersection with the second plane is determined, the direction along this line of intersection will be the direction of the magnetic field H.

As the superconducting material constituting the base of the sensor used in the method of the present invention, it is preferable to use a material that has a high critical current density and has a sufficiently large Meissner effect.

In the above example, the critical current density determined by the DC four-probe method was about 200 [A/cm2].

If the base body 1 is made of a superconductor with a significantly low critical current density, for example a poorly sintered ceramic superconductor, the directivity of the applied magnetic field will be poor, and the magnetic sensing surface 1a Even when a magnetic field is applied perpendicular to the magnetic sensing surface, the same level of sensitivity can be obtained as when a magnetic field is applied parallel to the magnetic sensing surface. This is thought to be because the critical current of the superconductor is small, so the shielding current (superconducting current to maintain perfect diamagnetism) that can flow becomes small, and magnetic flux enters from a relatively small magnetic field.

In other words, when a porous ceramic superconductor is used, the Meissner effect is very weak, so even when a weak magnetic field is applied, magnetic flux penetrates into the superconductor, causing the abnormality obtained in the above example. This seems to be due to the fact that the directionality cannot be obtained.

In the above example, YBa2 Cu3O7 was used as the oxide superconductor constituting the substrate 1, but other oxide superconductors, such as Bi2 Sr2 Ca2 Cu3 Oy
, (Bil-x Pbx) 2
Sr2 Ca2 Cu3O1, or T i 2
B a 2 Ca 2 Cu gl Oy, etc. can also be used.

In the above embodiment, the current electrode q2 and the voltage electrode q3 are provided separately, but as shown in FIG. q
An electrode Q23 similar to 1 may be provided, and this electrode Q23 may be used both as a current electrode and a voltage electrode.

In the above embodiment, all the electrodes were provided on the magnetic sensing surface, but when the current electrode q2 and the voltage electrode q3 are provided separately, only the common electrode q1 that picks up the influence of the magnetic field is provided on the magnetic sensing surface, Other electrodes may be provided on other surfaces.

As shown in FIG. 9, an electrode q23 similar to the common electrode q1
If the electrode Q23 is to serve as both a current electrode and a voltage electrode, the electrode Q23 should be It is necessary to provide it on the same magnetic sensing surface as the common electrode q34. In this case, since both electrodes q1 and q23 influence the magnetic detection voltage, sensitivity can be increased.

In the above embodiments, an oxide superconductor was used as the superconductor, but a metallic superconductor may also be used.

Furthermore, in the above embodiments, the base of the sensor is constructed from a block of superconductor, but a thin film of superconductor formed on a substrate can also be used as the base of the sensor.

In the above embodiment, the sensor is first rotated around the z-axis, but the direction of the rotation axis when the sensor is first rotated is arbitrary.

The measurement method of the present invention is suitable for measuring weak magnetic fields, and can be applied to geomagnetism measurements, attitude meters that measure geomagnetism to detect the attitude of flying objects (artificial satellites, airplanes, etc.), geomagnetic measurements, etc. I can do it. In the industrial field, it can also be applied to measuring the position and angle of rotating bodies, measuring displacement, detecting iron pieces, magnetic flaw detection, etc. using magnetism.

[Effects of the Invention] As described above, according to the present invention, the Meissner effect of a superconductor is used to impart directionality, and the change in the resistance value of the junction due to the penetration of the magnetic field is used to reduce the magnetic field. There is an advantage that the direction and strength of a weak magnetic field can be measured with high accuracy using a sensor with a simple configuration that obtains a magnetic detection voltage depending on the magnitude.

[Brief explanation of the drawing]

1 to 9 show embodiments of the present invention,
Fig. 1 is a block diagram showing the configuration of the sensor of the present invention, Figs. 2 and 3 are explanatory diagrams explaining the operation of the sensor used in the present invention, and Fig. 4 shows the temperature change during heat treatment of the sensor. The diagrams shown in FIGS. 5 and 6 are diagrams showing the relationship between the current flowing through the sensor used in the present invention and the magnetic detection voltage, and the relationship between the magnetic detection voltage and the magnetic field, respectively, and FIG. FIG. 8 is a perspective view illustrating an example of how to determine the rotation axis of the sensor used, FIG. 8 is an explanatory diagram illustrating the procedure for rotating the sensor in a magnetic field, and FIG. 9 shows a modification of the sensor used in the present invention. FIG. 1...Base, 2...Sensor, 3...Constant current source, 4
... Voltage detection means, ql... Common electrode, q2...
Current electrode, q3...voltage electrode. Figure 3 Figure 5 Magnetic detection at pressure (mV+

Claims (7)

[Claims] (1) Using a sensor in which a common electrode made of a normal conductor metal, a current electrode, and a voltage electrode are bonded to a base made of a superconductor, and at least the surface on which the common electrode is provided is a flat magnetic sensing surface, means for flowing a constant current through the common electrode and the current electrode; and voltage detection means for detecting a voltage generated between the common electrode and the voltage electrode while the constant current is flowing as a magnetic detection voltage; Maintaining the temperature of the sensor below the critical temperature of the superconductor, changing the attitude of the sensor in the magnetic field to be measured to determine the maximum and minimum values of the magnetic detection voltage, and determining the maximum and minimum values of the magnetic detection voltage. A method for measuring a magnetic field, characterized in that the strength of the magnetic field to be measured is determined from the difference from a minimum value. (2) Using a sensor in which a common electrode made of a normal conductor metal, a current electrode, and a voltage electrode are bonded to a base made of a superconductor, and at least the surface on which the common electrode is provided is a flat magnetic sensing surface, means for flowing a constant current through the common electrode and the current electrode; and voltage detection means for detecting a voltage generated between the common electrode and the voltage electrode while the constant current is flowing as a magnetic detection voltage; Maintaining the temperature of the sensor below the critical temperature of the superconductor, determining the central axis of rotation of the sensor, and rotating the sensor around the first axis in the magnetic field to be measured until the magnetic detection voltage is maximized. Find a position as a reference position, then rotate the sensor around a second axis perpendicular to the magnetic sensing surface of the sensor at the reference position to find the minimum and maximum values of the magnetic detection voltage, A method for measuring a magnetic field, characterized in that the strength of the magnetic field to be measured is determined from the difference between a maximum value and a minimum value of the detected voltage. (3) Using a sensor in which a common electrode made of a normal conductor metal, a current electrode, and a voltage electrode are bonded to a base made of a superconductor, and at least the surface on which the common electrode is provided is a flat magnetic sensing surface, means for flowing a constant current through the common electrode and the current electrode; and voltage detection means for detecting a voltage generated between the common electrode and the voltage electrode while the constant current is flowing as a magnetic detection voltage; Keep the temperature of the sensor below the critical temperature of the superconductor, change the attitude of the sensor in the magnetic field to be measured, find the position where the magnetic detection voltage is minimum as the minimum detection voltage position, and calculate the position at the minimum detection voltage position. A method for measuring a magnetic field, comprising detecting a direction perpendicular to the magnetic sensing surface as the direction of the magnetic field to be measured. (4) Using a sensor in which a common electrode made of a normal conductor metal, a current electrode, and a voltage electrode are bonded to a base made of a superconductor, and at least the surface on which the common electrode is provided is a flat magnetic sensing surface, means for flowing a constant current through the common electrode and the current electrode; and voltage detection means for detecting a voltage generated between the common electrode and the voltage electrode while the constant current is flowing as a magnetic detection voltage; Maintaining the temperature of the sensor below the critical temperature of the superconductor, determining the central axis of rotation of the sensor, and rotating the sensor around the first axis in the magnetic field to be measured until the magnetic detection voltage is maximized. Then, the sensor is rotated around a second axis perpendicular to the magnetic sensing surface of the sensor at the reference position, and the position where the magnetic detection voltage is minimum is determined as the minimum detection voltage position. A method for measuring a magnetic field, characterized in that a direction perpendicular to the magnetic sensing surface of the sensor at the minimum detection voltage position is detected as the direction of the magnetic field. (5) Using a sensor in which a common electrode made of a normal conductor metal, a current electrode, and a voltage electrode are bonded to a base made of a superconductor, and at least the surface on which the common electrode is provided is a flat magnetic sensing surface, means for flowing a constant current through the common electrode and the current electrode; and voltage detection means for detecting a voltage generated between the common electrode and the voltage electrode while the constant current is flowing as a magnetic detection voltage; Maintaining the temperature of the sensor below the critical temperature of the superconductor, determining the central axis of rotation of the sensor, and rotating the sensor around the first axis in the magnetic field to be measured until the magnetic detection voltage is maximized. The sensor is then rotated around a second axis that intersects the magnetic sensing surface of the sensor at the reference position, and the position where the magnetic detection voltage is maximum is determined as the maximum detection voltage position. , detecting as the direction of the magnetic field a direction along a line of intersection between a first plane along the magnetic sensing surface of the sensor at the reference position and a second plane along the magnetic sensing surface of the sensor at the maximum detection voltage position; A magnetic field measurement method characterized by: (6) The method for measuring a magnetic field according to any one of claims 1 to 5, wherein the metal is selected from the metal group consisting of gold, silver, platinum, and alloys thereof. (7) The oxide superconductor is YBa_2Cu_3O_7
____δ, Bi_2Sr_2Ca_2Cu_3O_y,
(Bi_1_-_xPb_x)_2Sr_2Ca_2C
u_3O_y_′, or Tl_2Ba_2Ca_2C
7. The method for measuring a magnetic field according to claim 1, wherein the magnetic field measuring method is made of a ceramic or a thin film of u_3O_y_'.