JPH0799385B2 - Superconducting magnetic field detector - Google Patents

Description

The present invention relates to a superconducting magnetic field detecting element for detecting a weak magnetic field with high sensitivity.

<Prior Art> Conventionally, as a method of detecting magnetism, for example, a magnetoresistive effect element using a semiconductor or a magnetic material has been widely used. Particularly, a shape effect and a ferromagnetism of a semiconductor InSb, InAs or the like having a high electron mobility are used. Devices using orientation effects of body metals Fe-Ni (permalloy), Co-Ni, etc. have been put to practical use.

The rate of change in resistance to the magnetic field of the magnetoresistive effect element using the semiconductor InSb, InAs described above has a characteristic along a square curve as shown in FIG. 6, and the magnetoresistive effect element made of the ferromagnetic metal Fe--Ni The rate of change in resistance with respect to the magnetic field is shown in FIG.

<Problems to be Solved by the Invention> However, in the conventional magnetoresistive effect element described above, for example, as shown in FIG. 6, when the magnetic field is weak, the resistance change is small, and therefore, as shown in FIG. Although a magnetic bias is applied in advance by a permanent magnet etc. to improve the sensitivity, in any case, the conventional magnetoresistive effect element has extremely low sensitivity for detecting a weak magnetic field and operates with high sensitivity to a weak signal magnetic field. There has been a demand for the development of a detection element that does.

The present invention was devised in view of the above points, and has excellent high-sensitivity characteristics of detecting weak signal magnetic fields with high sensitivity and acting based on a novel phenomenon different from conventional detection elements. It is intended to provide a superconducting magnetic field detecting element.

<Means and Actions for Solving Problems> In order to achieve the above object, the superconducting magnetic field detecting element of the present invention is composed of superconducting particles, and a grain boundary or a part of the particles is a normal conducting material or an insulator. Alternatively, a superconducting ceramic layer containing a superconducting substance that becomes a normal conductor by a magnetic field, a pair of first electrodes for passing a current through the superconducting ceramic layer, and a pair of second electrodes for detecting a voltage. The coherent length, which represents the wave region exhibiting superconductivity due to the low magnetic field, is shortened and the tunnel effect is not exhibited, so that a sharp resistance change is exhibited.

In an ideal superconducting state, the superconductor has zero electric resistance and exhibits a minus effect. Therefore, within the critical magnetic field, the internal magnetic field of the superconductor does not enter, and resistance change cannot occur. However, if the superconductor is configured so as to include a part of the normal conductor material, an insulator, or a substance that becomes a normal conductor due to a magnetic field, current will flow on the surface of the superconductor in the magnetic field, and the coherent length will be shortened. Since the tunnel effect disappears, the state of zero resistance collapses and the resistance increases, and the magnetic field is detected with high sensitivity.

The superconducting magnetic field detecting element of the present invention controls grain boundaries, bubbles, and composition in the production of a high-temperature superconductor ceramic layer, and the detection sensitivity near the magnetic field zero is completely different from that of a conventional magnetoresistive element made of a semiconductor or a magnetic material. It embodies high-sensitivity magnetic detection based on the principle. That is, in the superconducting magnetic field detecting element of the present invention, a part of the superconductor contains a normal conducting material, an insulator, or a substance which becomes a normal conducting body in the magnetic field, and the magnetic field shortens the coherent length (wave region indicating superconductivity). Since the tunnel effect is eliminated, the magnetic field is detected with high sensitivity, and the sensitivity characteristic shows a sharp resistance change with respect to a weak magnetic field, unlike the conventional magnetoresistive effect element.

<Examples> Hereinafter, the present invention will be described in detail with reference to Examples.

First, a superconducting ceramic layer used in one embodiment of the present invention, that is, a normal conductive material at a grain boundary or a part of a particle,
In order to obtain a superconducting ceramics layer containing a superconducting substance which becomes an ordinary conductor by an insulator and / or a magnetic field, a ceramics layer was formed by the following steps.

First, in order to obtain a Ba ₂ Y ₁ Cu ₃ Ox-based superconductor, which was recently announced as a high-temperature superconductor, a predetermined amount of BaCO ₃ , Y ₂ O ₃ and CuO was weighed and finely dispersed and mixed at 900 ° C. Calcination was performed in air for 5 hours. Next, pulverize and disperse again to make a powder consisting of uniform fine particles (1 μmφ or less), and apply a pressure of 1 ton / cm ²
Then, circular pellets were prepared. For pressure molding, the powder may be placed in a rubber-like holder to produce pellets under hydrostatic pressure. Next, the main calcination was held in sufficient oxygen for 3 hours at 1000 ° C., and the temperature was lowered to 200 ° C. for 5 hours to prepare a sample A in the form of pellets used in the examples of the present invention. In addition, the same pre-baked sample is used in the air, which is a conventionally known general condition.
Hold at 0 ℃ for 200 hours and slowly cool down to 200 ℃ (3 ℃ /
Comparative sample B in the form of pellets was prepared. X
In macroscopic material evaluation by line diffraction, sample AB was also an orthorhombic single phase.

Next, as shown in FIG. 1, a pair of first electrodes for applying an electric current to the surface of the superconducting ceramic layer 1 of Sample A.
2,2 and a pair of second electrodes 3,3 for detecting voltage, Ti electrodes with good adhesion are vapor-deposited and attached, and silver pastes 4,4,5,5 are further attached to those electrodes. To fix the lead wires to produce a superconducting magnetic field detection element, and connect each lead wire to the constant current circuit 6
And the detection output circuit section 7. Similarly, for Comparative Sample B, a Ti electrode having good adhesion was vapor-deposited, and a lead wire was fixed on the Ti electrode with silver paste.

In microscopic observation with an electron microscope, the comparative sample B is a ceramic consisting of particles having a relatively roundness (3 to 5 μmφ), but the sample A according to the present invention has a roundness particle as shown in FIG. Rectangle other than 11 (3 × 3 × 10μ
The particles 12 of m) are also partially included, and the rectangular particles 12 have a larger Cu composition and a smaller composition of Ba and Y than the particles 11 (Y ₁ Ba ₂ Cu ₃ Ox) having a uniform composition. Particles made of a normal conductor or an insulator or a superconductor material that becomes a normal conductor by a magnetic field.Grain boundaries or intergranule 13 containing impurities exist between particles 11 and 12, and bubbles 14 also exist. It was in a state of doing.

Next, the sample A and the comparative sample B were put into liquid nitrogen (77K), and the electrical resistance was measured by the four-terminal method. When there is no magnetic field, the resistance is zero in both sample A and comparative sample B. Further, the comparative sample B showed zero resistance even when a magnetic field was applied up to 0.5 K gauss. However, in the sample A according to the present invention, the change in resistance appears with high sensitivity to a magnetic field of several tens of gausses, and the change with respect to the magnetic field is the change in resistance with respect to the magnetic field of the conventional magnetoresistive sensor such as a semiconductor or a magnetic material ( 6 and 7), the characteristics are not along the square curve as shown in FIG. 6, but the characteristics are quite different and steep as shown in FIG. 4. Therefore, as shown in FIG. The resistance change in the vicinity of the zero magnetic field was steep and extremely large. Further, these characteristics were reproducible for the samples prepared under the same composition and the same heat treatment condition.

According to the detecting element of the above embodiment, a steep resistance change characteristic can be obtained, and this operation can be explained as follows based on the structure of the superconductor ceramic layer of the present invention. That is, the rounded particles 11 are superconductors, but the grain boundaries 13 and the rectangular particles 12 are not the same superconductors as the particles 11 (normal conducting materials, insulators, superconducting materials that become normal conducting due to weak magnetic fields). Etc.), when there is no external magnetic field, the current passes through the grain boundaries 13 and the rectangular particles 12 due to the tunnel effect, and the entire ceramic body is in a superconducting state, but when an external magnetic field is applied, it is shown in FIG. The coherent length (wave region indicating superconductivity) becomes shorter as a result, resulting in grain boundaries 13 and rectangular particles 12
The current no longer passes through, a resistance appears, and the magnetic field sensitivity is exhibited. In FIG. 3, the solid line a shows the coherent length when the magnetic field is zero, and the broken line b shows the coherent length when the magnetic field is applied.

In addition, in the above-mentioned example, the superconducting ceramics were filled under 90% or less and the surface roughness was 1 μm under the same conditions except that the pressure was changed to 0.5 ton / cm ² to form circular pellets. It has been found that the sensitivity is improved with respect to the magnetic field. Further, it has been found that the sensitivity to the magnetic field is improved by setting the filling rate to 85% or less, increasing the number of open cells 14 (see FIG. 2), or by making fine holes with a laser.

Further, as shown in FIG. 5, even if the sample A is cut by dicing and processed into a small element 21 of 1 × 2 mm square, the same characteristics are exhibited, and it is possible to cope with a mass production process. A small-sized superconducting magnetic detection element in which a circuit board 28 including a constant current circuit 24 and an amplifier 25 and the present element 21 were connected by a lead wire 27 was prototyped and the operation of the present invention was confirmed.

In the above embodiments, the Y-Ba-Cu-O system was described as an example of the superconducting ceramics, but the present invention is not limited to this, and for example, La-Ba-Cu-O system, Y- system.
Group IIIa elements such as Sr-Ba-Cu-O system, IIa group elements, copper (C
It goes without saying that the same can be done by using superconducting ceramics containing u) element and oxygen (O) element as constituent elements.

<Effects of the Invention> As described above, the superconducting magnetic field detecting element of the present invention is completely different from the conventional element characteristics in that it can detect a magnetic field with a high sensitivity to a minute magnetic field, and it can operate at high speed regardless of the polarity of the magnetic field. To respond.

With the progress of the critical temperature of high-temperature superconductors in the future, the high-sensitivity magnetic field detection element of the present invention will be applied to a wide range of fields such as measurement, medical, and industrial fields that require reliability, stability, and high sensitivity. .

[Brief description of drawings]

FIG. 1 is a perspective view showing a basic structure of an element of an embodiment of the present invention, FIG. 2 is a view schematically showing a microscopic structure of a superconductor ceramic layer used in an embodiment of the present invention, and FIG.
FIG. 4 is a diagram for explaining the operation of the element of the present invention, and FIG. 4 is a characteristic diagram showing the resistance change with respect to the magnetic field of the element of one embodiment of the present invention,
FIG. 5 is a perspective view showing a superconducting magnetic field detecting element having a structure in which an element as another embodiment of the present invention is made into a chip and integrated with a cooling device and a circuit device part, and FIG. 6 is a magnetoresistive effect made of a magnetic material. FIG. 7 is a characteristic diagram showing the resistance change rate of the element with respect to the magnetic field, and FIG. 7 is a characteristic diagram showing the resistance change rate of the magnetoresistive element made of a semiconductor with respect to the magnetic field. 1 ... Superconductor ceramics, 2,2 ... First electrode, 3,3
...... Second electrode, 4,4,5,5 ...... Silver paste, 6 ...... Constant current circuit, 7 ...... Detection output circuit section.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-59-17175 (JP, A) C.I. W. Chu, et al. : Phy s. Rev. Lett. Vol. 58 No. 4,26 January 1987 P.P. 405-407

Claims (3)

[Claims] 1. A superconducting ceramic layer comprising superconducting particles, wherein a grain boundary or a part of the grain contains a superconducting substance, an insulator, or a superconducting substance which becomes a normal conducting state by a magnetic field, and the superconducting ceramic layer. It is provided with a pair of first electrodes for passing an electric current and a pair of second electrodes for detecting the voltage of the superconductor ceramic layer, and the coherent length representing the wave region indicating superconductivity is shortened by a low magnetic field. A super-electric magnetic field detecting element characterized by exhibiting a sharp resistance change by not exhibiting the tunnel effect. 2. The surface roughness of the superconductor ceramic layer is 1
The first aspect of the present invention is characterized in that the thickness is at least μm.
A superconducting magnetic field detecting element described in the paragraph. 3. The superconducting magnetic field detecting element according to claim 1, wherein the superconducting ceramic layer contains fine open cells therein.