JPH01217282A - Magnetic field detector - Google Patents

Abstract

PURPOSE:To obtain a magnetic field detector having ultrahigh sensitivity, strong against heat stress and hard to break, in constituting a sensor, by providing a part having high current density to a part of a ceramic type oxide superconductor changing in its magnetic flux flow resistance by the application of a magnetic field. CONSTITUTION:A substrate is formed by compounding about 1.0g of CuO, about 0.6g of Y2O3 and about 1.5g of BaCO3 according to powder metallurgy and shows the second-class superconductivity. A long window 3 is opened to the center of a disc and a part 2 where the cross-sectional area of the substrate becomes small is provided in the vicinity of the apex part 4 of the long window. A pair of current inflow and outflow electrodes 5, 5' are provided to both ends of the substrate 1 and a pair of voltage detecting electrodes 6, 6' are provided on both sides of a current passage narrow part 2. A circuit is formed by connecting a variable voltage DC power supply 11, a stable resistor 12 and a current detecting small resistor 13 to the apparatus 10 thus constituted. By detecting the potential difference between the electrodes 6, 6', the magnetic field of the current passage narrow part 2 is detected.

Description

[Detailed description of the invention] [Industrial application fields] In the present invention, a type 2 superconductor is influenced by a magnetic field.

The present invention relates to a small, lightweight, ultra-high-sensitivity magnetic detector constructed by applying the phenomenon in which magnetic flux flow resistance increases, and can be widely used in various magnetic detection applications such as magnetocardiograms that require ultra-high sensitivity.

[Prior art] As an ultra-sensitive magnetic field detector, there is a superconducting quantum interference device (hereinafter referred to as 5QUID) that utilizes a so-called Josephson junction, in which superconductors are bonded to each other with a thin insulating film in between.
has been put into practical use. 5 using this Shosefson junction
QUID has a detection resolution of 16 degrees or less, which is currently the highest detection resolution. However, this 5QUI
The thickness of the insulating film required to form the Josephson junction used in D is typically several tens of nm, and 5QUID is generally used at a low temperature of 4 nm, so and low i'! (4K) and is subject to thermal and mechanical stress due to repeated back and forth between the superconductors and the superconductor. It was extremely difficult to do so. On the other hand, recently, high-temperature oxide superconductors using ceramic materials have been discovered one after another, and the critical temperature for exhibiting a superconducting state is 77 or 10K.
Something that shows the before and after has been realized.

This ceramic superconductor is made by homogeneously mixing and molding oxides such as bismuth, yttrium, barium, calcium, aluminum, and copper.
The common method is to bake at a high temperature of around °C, which tends to cause unevenness on the surface, making it difficult to obtain a surface sufficiently smooth to uniformly form an insulating film several nanometers thick. . Therefore, although this ceramic superconductor has a remarkable critical temperature of 100K or more, it is difficult to form a Josephson junction that exhibits stable operating characteristics, so SQ
The application to [I[D, etc.] is closed.

[Problems to be Solved by the Invention] Therefore, the present invention develops a magnetic field detection method that takes advantage of the characteristics of superconductors, particularly type 2 superconductors found in ceramic oxide superconductors, which have extremely high detection resolution. It is about providing the equipment.

Although the 5QUID using a Josephson junction has ultra-high resolution as a magnetic field detector, it is difficult to obtain a Josephson junction that exhibits stable operating characteristics. In addition, since stable operation was obtained at around 4 kHz, an expensive refrigerant called helium was required. On the other hand, ceramic-based oxide high-temperature superconductors whose critical temperature exceeds 100 K, which has recently been discovered as a phase-detachable material, are sintered bodies, so it is difficult to obtain a smooth surface, and at the same time, it is difficult to obtain a stable ultra-thin insulating layer. Therefore, it is extremely difficult to form 5QUID with stability and good reproducibility. Recently, research and development has been carried out on so-called "micro bridge" type planar elements with thinner joints, but stable operation has not yet been achieved.

Therefore, an object of the present invention is to provide a magnetic field detection device that is ultra-highly sensitive and hard to break, taking advantage of the characteristics of a ceramic oxide high-temperature superconductor that does not require an expensive refrigerant called helium.

[Means for solving the problem] Focusing on the phenomenon in which ceramic and phosphorus-based oxide superconductors exhibit magnetic flux flow resistance peculiar to second superconductors, we created a current path narrow part in a part of the substrate that exhibits superconductivity. The structure is such that the magnitude of the magnetic flux flow resistance changes easily depending on the magnetic field. When a magnetic field is applied to the narrow part of the current path in a direction perpendicular to the current path, the magnetic flux flow resistance increases (a phenomenon discovered by the inventors), and the magnitude of the applied magnetic field or its change is measured by potential difference. This is done by

The increase in magnetic flux flow resistance due to the applied magnetic field can be observed by potentiometric measurement, and the correspondence relationship is highly sensitive and reproducible.

The superconductor may be a type 2 superconductor, such as YBaC, which has recently been discovered and exhibits high critical temperature characteristics.
uO system or B1BaCuCaO system, BIBaCuA
Since a ceramic-based oxide high-temperature superconductor typified by IO-based superconductors is used, the manufacturing process is easy, miniaturization is possible, and there are fewer problems such as breakage.

[Operations] The observed facts that formed the basis of this invention will be explained using diagrams.

FIG. 1 shows a general configuration for the device of the invention and a circuit for measuring its characteristics. The device for the present invention has a base portion l made of a substance exhibiting type 2 superconductivity,
A part of it is provided with a portion 2 having a high current density. In the illustrated embodiment, the cross-sectional area perpendicular to the current passing direction is made small. That is, the substrate I is Cu01.0g
A long window 3 is opened in the center of a disc formed by powder metallurgy with a blend of 1Y2030 and 1.5 g of Gg1BaCO3, and the disc is divided into two in a direction perpendicular to the long window. A portion 2 is formed in which the cross-sectional area of the base body becomes smaller. This narrow part of the current path is
It doesn't have to be very short. In the embodiment, the substrate 2
The diameter of the long window 3 is IOmm, the width of the long window 3 is 2Ill11, and the height is about 3mm.

A pair of electrodes 5, 5' for current inflow and current outflow are provided at both ends of the base 1 made of a second type superconductor. The electrodes were formed using indium (In) by ultrasonic soldering.

Although this electrode is an ohmic electrode, it is not essentially required to be an ohmic electrode.

Further, a pair of voltage detection electrodes 6.6' are provided on both sides of the current path narrow portion 2 of the base body 1. This method also applies to electrode 5.
, 5'.

The circuit consists of a variable voltage DC power supply 11, a stabilizer resistor 12 (5Ω
It is constructed by connecting in series a small current detection resistor 13 (about IΩ) and the device IO of the present invention.

FIG. 2 is a diagram showing the voltage versus current characteristics of the device IO of the invention. The horizontal axis shows the potential difference V (mV) between the electrodes 6 and 6', and the vertical axis shows the total current I (mA) of the circuit measured using the resistor 13. The characteristic where the voltage vs. current characteristic on the lower side shows a straight line is the measurement result at room temperature, and this region is
The normal conduction state (N-state) is shown. Next, the base plate is cooled to a superconducting state. In a range where the passing current is small (80 IIA or less), a superconducting state (S-state) occurs in which no potential difference occurs even when current flows. However, when the passing current increases, that is, the critical current lc (80mA
), the conduction state of the substrate 1 changes and the critical current 1
At a current somewhat greater than c, a voltage nearly proportional to the increasing current occurs. This phenomenon is due to the magnetic flux flow resistance observed in type 2 superconductors, and this experimental fact indicates that the ceramic oxide superconducting couple is a type 2 superconductor. is in a normal conducting state (partall
y Normal, p, N-state).

The device of the present invention has the following advantages: In the mixed region of the superconducting state and the normal conducting state (p, N-state) peculiar to the second type superconductor,
When a magnetic field is applied in a direction perpendicular to the current passing direction (arrow B in FIG. 1), the superconducting and partially normal conducting states change, and the phenomenon is utilized that the magnetic flux flow resistance increases. This phenomenon was discovered by the inventors in ceramic-based oxide high-temperature superconductors.

FIG. 3 shows this phenomenon, and shows the change in characteristics when the S or N pole of the permanent magnet is brought closer to the base 1. The horizontal axis shows the distance x (ci+) between the permanent magnet and the substrate l, and the vertical axis shows the change in potential difference ΔV (mV) between the electrodes 6-6'.

The current was constant at 200 mA. Apart from the distance X, the horizontal axis is a scale of magnetic flux density B. When the distance between the magnetic poles is sufficiently large (X: 4c), there is no significant change in potential difference, but as X becomes smaller, the magnetic flux flow resistance increases, and at 175XIQ'(T), a change in potential difference of GiV is obtained. ing. Both when the south poles are brought closer together and when the north poles are brought closer together, the results are consistent within the experimental error range. Moreover, reproducibility was also obtained. The relationship between magnetic flux density and potential difference is 0.4 (V/T) at its steepest point, and this value is higher than the detection resolution of 5QUID at a conventional helium temperature of 4 ~
Although it is inferior to 10' (V/T), compared to a Hall element whose detection resolution is -9=high 100 nT, an improvement in sensitivity of approximately two orders of magnitude or more was achieved above the liquid nitrogen temperature.

In addition, the following phenomenon was discovered through another experiment.

In other words, Fig. 4 shows the same device IO used in Fig. 1, when it is brought to a low temperature and brought into a superconducting state, and then the N pole of a strong magnetic field (0, I57) is brought close once and the magnetic field is removed. Curve A was obtained as voltage/current characteristics. The same properties are obtained when a similar magnetic field is applied, the temperature is then lowered, and the magnetic field is removed. This state is
Unlike the p,N state of FIG. 1, this means that the applied strong magnetic field is stored in this device IO. That is, this device has the property of memorizing magnetic fields.

Next, a weak magnetic field was applied in the direction of the arrow 7 in FIG. 1 to the device 10 in the state shown in FIG. 4A. When we bring the weak north pole closer together, the characteristic becomes a broken line B, and when we remove the magnetic field, we see the characteristic curve A again.
is obtained. This time, when the weak south pole is brought closer, the characteristic becomes a broken line C, and when the magnetic field is removed, the characteristic curve A is obtained again.

FIG. 5 is a separate diagram showing the situation at that time. The horizontal axis is the distance mx (crn) from the device IO to the magnetic pole or the magnetic field B (T ), and the vertical axis is the change in potential difference ΔV CV ) when a current of 200 mA is passed through the device IO. The broken line indicates when X is decreased (the magnetic poles are brought closer together), and the solid line is indicated when X is increased (the magnetic poles are moved away).

That is, it can be seen that the memory of exposure to a strong magnetic field is not erased by the application of a small magnetic field.

[Example] A first example is shown in FIG. Also, how to make it
This is as described in the [Operation] section.

The essence of this invention is that the magnetic flux flow resistance of a type 2 superconductor in which a part of the normal conduction state is mixed in the superconductor increases by the application of a magnetic field. We are focusing on phenomena. Therefore, it is sufficient to create a portion with high current density that is easily exposed to the magnetic field.

In the embodiment shown in Fig. 1, a disk-shaped base was processed for ease of manufacture, or a rod-shaped base with a constriction in the current path was used, and the cross-sectional shape of the rod was not limited to a circle, but could also be square or rectangular. That's fine.

Using the observational facts shown in Figures 4 and 5, it can be determined that the device IO shown in Figure 1 above can be used as a magnetic field storage device that stores the fact that a strong magnetic field of a predetermined level has been applied. ] was explained in the section. Therefore, the device 10 is controlled by means for measuring the voltage/current characteristics of the magnetic field storage device (for example, a current measuring device, a potential difference measuring device, and a determining device).
By observing the conduction state of the material exhibiting superconductivity used for this purpose, it is possible to detect whether or not a strong magnetic field of a predetermined level or higher has been applied to the device IO.

[Effects of the Invention] This invention provides a part of a type II superconductor with a region where the current density is higher than the other part (current path narrow part) over a considerable length (for example, visible to the naked eye), and We have discovered and utilized the phenomenon in ceramic-based oxide high-temperature superconductors that when a magnetic field is applied in a direction perpendicular to the current in a region, the magnetic flux flow resistance changes markedly. Therefore, it has become possible to detect a magnetic field with a high sensitivity of 0°1l-4V/T or higher, which is unprecedented in the past, at a temperature higher than liquid nitrogen temperature.

Furthermore, the substrate can be made by, for example, powder metallurgy, and small pieces can be produced in large quantities.

In addition, damage to the substrate due to thermal stress can be reduced.

Therefore, we have improved the drawbacks of conventional elements of this type,
Moreover, we have realized a highly sensitive weak magnetic field detection device. (First claim) Furthermore, it has been discovered that the device 10 of the present invention (first claim) can memorize the fact that a strong magnetic field of a predetermined level has been applied. was also achieved. (Second claim)

[Brief explanation of the drawing]

FIG. 1 is an embodiment of the present invention and a circuit diagram for measuring the characteristics of the device of the present invention using the same, FIG. 2 is a diagram showing the characteristics of an embodiment of the present invention, FIG. FIGS. 4 and 5 are diagrams showing how an embodiment of the present invention reacts to a magnetic field. In the figure, ■...base, 2...current path narrow part. 5.5'...Electrode for current inflow (outflow). 6.6゛...Electrode for potential difference detection. ■...Indicates a magnetic field storage device.

Claims (2)

[Claims] (1) A substrate made of a material exhibiting superconductivity and having a structure in which a part of the current path has a narrow current path part and can be exposed to a magnetic field in a direction perpendicular to the current flowing through the narrow part of the current path ( 1
); a pair of electrodes (5, 5') that allow current to flow into or flow out of the base; a pair of potential difference detection electrodes provided across the narrow current path of the base; A magnetic field detection device consisting of electrodes (6, 6'). (2) A substrate (1 )
A pair of electrodes (5, 5') that allow current to flow into or flow out of the base; A pair of potential difference detection electrodes provided across the narrow current path of the base. (6, 6'); a magnetic field storage device (¥10) that stores the applied magnetic field at a predetermined level as its voltage/current characteristics; and means for measuring the voltage/current characteristics of the magnetic field storage device; A magnetic field detection device that detects the presence or absence of a magnetic field applied to a magnetic field storage device.