JPH0671100B2 - Superconducting magnetoresistive device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a magnetoresistive device using a magnetoresistive element exhibiting excellent characteristics unprecedented. More specifically, a superconducting material is used. The present invention relates to a magnetoresistive device.

<Prior Art and Problems Thereof> Conventionally, as a magnetoresistive element that exhibits an increase in electric resistance by applying a magnetic field, there are one using a semiconductor and one using a magnetic body. However, in each case the 25th
As shown in the figure, the original large resistance R ₀ is exhibited even when no magnetic field is applied, and the rate of change in resistance with respect to the magnetic field is a characteristic along a square curve. The resistance increase ΔR is extremely small for a magnetic field having a small value, for example, a weak magnetic field of about several tens of gausses, because it increases in proportion to the square of
R / R ₀ was at most about 1%.

On the other hand, SQUID (superconducting quantum interference device) utilizing superconductivity is known to have extremely high sensitivity (10 ⁻¹⁰ Gauss), but requires an extremely delicate structure,
Moreover, its usage was not simple.

Therefore, conventionally, it exhibits a high resistance change with respect to a weak magnetic field. Moreover, it has been desired to develop a magnetoresistive device having a simple structure.

Also, as a document describing the magnetic properties of superconducting materials, Ph. Rev. Lett. 58 [4] (26) by CW Chu et al.
Jan. 1987) pp.405-407 are known. This document describes that the magnetic characteristics based on the superconducting phenomenon at a temperature of 40 K or less in the La-Ba-Cu-O compound system were evaluated. As the method of preparing a La-Ba-CuO compound, a mixture of lanthanum oxide (La ₂ O ₃₎ and copper oxide (CuO) and barium carbonate (BaCO _3), heated and held in an oxygen atmosphere at reduced pressure After that, this is pulverized, these steps are repeated, and the completely reacted mixture is pressurized into a cylindrical shape, and is sintered in an oxygen atmosphere under reduced pressure as in the previous step. . Then, the La- produced as described above
When a very strong magnetic field of 0, 4.5, 15, 30, 58.5k gauss was applied to the Ba-Cu-O compound, 40
The results of measuring the change in electric resistance when cooled to a temperature of K or less are described.

However, the compound system as shown in the above-mentioned document forms a multiphase, and the principle of the resistance change with respect to the magnetic field is that, according to the consideration of the authors in the above-mentioned document, a mixed phase, Or it only suggests the effect of K ₂ NiF ₄ phase, which is one type of multiphase,
Not understood. Moreover, only the change of electric resistance was observed in a strong magnetic field of 4.5 k Gauss or more. Therefore, the superconducting material shown in the above-mentioned document cannot be expected to be applied to a magnetoresistive device which exhibits a high resistance change in a weak magnetic field.

The present invention has been made in view of the above points, and acts based on a novel phenomenon different from the conventional magnetoresistive element, and exhibits high-performance resistance change even in a weak magnetic field. An object is to provide a superconducting magnetoresistive device.

<Means for Solving Problems and Principle Thereof> In order to achieve the above object, the superconducting magnetoresistive device of the present invention has a large number of crystal grain boundaries, and crystal grains exhibiting superconductivity are electrically weak to each other. An element composed of a ceramic superconducting material that is coupled, means for applying a magnetic field to this element, and means for utilizing a change in electrical resistance that occurs when a magnetic field is applied to the element are configured. There is.

In the present invention, as the magnetoresistive element, an element made of a ceramic superconducting material having a large number of crystal grain boundaries and having superconducting crystal grains electrically weakly coupled to each other is used. When no magnetic field is applied as shown in
The electric resistance R ₀ of the element shows a value of zero completely, but when a certain critical magnetic field Hc is applied, the element suddenly shows the electric resistance, and a new phenomenon that the electric resistance rapidly increases with the increase of the applied magnetic field was used. The ratio of the change in resistance ΔR to the initial resistance R ₀ , ΔR / R _0, becomes infinite, and the magnetoresistive device is configured by using an element exhibiting high performance that is not comparable to the conventional magnetoresistive element. I am trying to do it.

That is, the direction of research on ceramic superconductors, which has been advanced by many research institutions in recent years, is to improve the critical temperature (T _c ), the critical magnetic field (H _c ), and the critical current (i _c ). The present inventors also conducted various studies on the above-mentioned ceramic superconductor, and as a result, a certain kind of this superconducting material (having a weakly bonded state between particles of the superconducting material) has an extremely weak magnetic field ( We found that the superconducting state of weak coupling is broken at several Gauss) and the electric resistance is shown, and it rapidly increases with the strength of the applied magnetic field, and we created a new superconducting magnetoresistive device using this low critical magnetic field phenomenon. is there.

The change characteristic of the electric resistance with respect to the application of the magnetic field as shown in FIG. 1 is the same as that of the ceramic superconducting material constituting the superconducting magnetoresistive element used in the present invention.
As shown in the figure, a crystal body composed of many superconducting fine particles 1 has an extremely thin insulator or resistor at the grain boundary 2, or the contact portion between the particles 1 and 1 is in a point state. That is, the grain boundaries are in point contact with each other, and the crystal grains exhibiting superconductivity are electrically weakly coupled, that is, in the so-called superconducting weak coupling state, and in the superconducting state, due to the tunnel effect or the like. , The electrons move freely and show zero electric resistance. That is, a polycrystalline superconducting material in a weakly coupled state such as a ceramic system can be regarded equivalently as an assembly of innumerable Josephson couplings 3, 3, ... As shown in FIG.

When a magnetic field is applied to such a material, the superconductivity of the Josephson couplings 3,3, ...
The weakly coupled state of superconductivity is broken by the application of a weak magnetic field, and the element comes to exhibit electric resistance, and the electric resistance increases as the strength of the magnetic field increases.

As is clear from the above principle, this property is
Are arranged randomly, so that they are determined by the absolute value of the magnetic field strength, without depending on the direction of the applied magnetic field.

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

First, a description will be given of a production example of an element made of a superconducting material having a crystal grain boundary used in the examples of the present invention.
The manufacturing method of the superconducting material used in the examples of the present invention is not limited to the manufacturing method described below.

Y ₁ Ba, which was recently announced as a ceramic high-temperature superconducting material
To obtain a ₂ Cu ₃ O _7-x superconductor, yttrium oxide Y ₂ O ₃ , barium carbonate BaCO ₃ , and copper oxide CuO were weighed in a predetermined amount and sufficiently dispersed and mixed in the particles at 900 ° C. for 5 hours in air. Pre-baking is performed with, and then pulverized and dispersed again to make a powder consisting of uniform fine particles (1 μmφ or less), and a pressing force of 1 ton.
circular pellets were prepared at a temperature of 1 / cm ² and then fired in air at 1000 ° C for 3 hours and then cooled to 200 ° C in 5 hours to obtain a thickness of 1
A circular pellet of mm was prepared.

The superconducting material produced as described above is an orthorhombic single phase in macroscopic material evaluation by X-ray diffraction, and many superconducting particles as shown in FIG. 2 are observed in an electron microscope. It can be regarded as a weakly-bonded aggregate of superconductors composed of 1, 1, ... And having extremely thin insulators or resistors at grain boundaries (grain boundaries) 2.

When no magnetic field is applied to the superconducting material produced as described above, the electric resistance begins to drop at an absolute temperature of 97 degrees and becomes completely zero at an absolute temperature of 83 degrees as shown in FIG. It was

Thin rectangular element (1 x
As shown in FIG. 5, titanium (Ti) electrodes 52 and 53 having good adhesiveness to the superconducting material are attached to each of the electrodes 52 and 53 by electron beam vapor deposition or the like.
The lead wires 54 and 55 were fixed to each by silver paste. Such an electrode structure had very good adhesion to the superconducting material and exhibited extremely good ohmic characteristics.

Next, the element 51 is placed in liquid nitrogen (77K), and the electrodes 52,
A predetermined current was supplied from a constant current source (not shown) via 53, and the voltage between the electrodes 52 and 53 was detected to measure the electric resistance. When the magnetic field 56 is not applied, the resistance of the element 51 is zero. However, when the magnetic field 56 is applied and a current is passed, as shown in FIG. 6, when the current is 50 mA, a magnetic field of about 10 Gauss is applied. The electric resistance suddenly appeared at, and the resistance of the element 51 rapidly increased as the magnetic field increased. When the current is 10 mA, the electric resistance suddenly appears when the magnetic field of about 100 Gauss is applied, and when the current is 100 mA, the electric resistance suddenly appears when the magnetic field of about 5 Gauss is applied, and as the magnetic field increases, The electric resistance increased sharply in the same manner.

Moreover, this characteristic was reproducible and extremely stable. Furthermore, these characteristics did not depend on the direction of the applied magnetic field.

In the present specification, an element as described above is called a superconducting magnetoresistive element, and a magnetoresistive device using this element is called a superconducting magnetoresistive device.

By supplying a constant current to the above element and detecting a change in electric resistance as a voltage change, it is possible to know the presence or absence and the magnitude of the applied magnetic field, and thus it can be used as a magnetic sensor. In this case, the electric resistance of the element has a great feature that it does not depend on the direction of the magnetic field.
This is an advantage of the present invention, which cannot be realized by a conventional magnetoresistive element using a semiconductor or a magnetic material, or SQUID using a superconductor.

Furthermore, the electric resistance of the element is completely zero from zero to a certain value of the applied magnetic field, and when the magnitude of the applied magnetic field exceeds a certain value, the electric resistance rapidly increases, showing digital and analog characteristics. This is also a characteristic not found in conventional elements, is suitable for picking up digital or analog magnetic signals, and a magnetic head can be constructed by the superconducting magnetoresistive device of the present invention.

In the configuration shown in FIG. 5, the current electrode and the voltage electrode are commonly used as a practical two-terminal element. However, in the case of performing a precise measurement, as shown in FIG. The electrodes 72, 72 and the voltage electrodes 73, 73 are preferably provided separately.

As a means for applying a magnetic field to the superconducting magnetoresistive element, a permanent magnet may be used, an electromagnet may be used, or a magnetic field component of electromagnetic waves may be used.

When the above-mentioned ceramic superconducting material is produced, the raw material is sufficiently dispersed and pulverized to obtain fine powder (μm
Pellets were produced from (φ or less), but as another production example, the ceramic superconducting material and the superconducting magnetoresistive material were prepared by controlling the powder particle size during dispersion and crushing to about 2 to 5 μmφ under the same composition and the same heat treatment conditions. A device was produced.

In this case, the critical temperature shows almost the same characteristics as the superconducting material produced by the above method, but the critical current is 15 A / cm in the previous example.
2 orders of magnitude compared to ² (0.05 A / cm ²⁾ decreases, measurement of the resistance change to the magnetic field by applying a magnetic field to the device,
As shown in FIG. 8, the sensitivity was extremely excellent, and the sensitivity could be sensitively controlled by controlling the applied current. That is, the threshold value of the magnetic field at which electric resistance suddenly appears was 30 gauss at an applied current of 1 mA, 5.5 gauss at 5 mA, and 0.2 gauss at 10 mA, as shown in FIG.

This phenomenon is because the superconducting materials prepared by the above two examples have the same composition and the same heat treatment process, but the starting materials with different particle sizes are used. And the critical current is different at the same time, in the latter case, in the weakly coupled state,
It is presumed that it occurs as a result of the superconducting tunnel effect becoming more sensitive to magnetic fields.

FIG. 10 is a diagram showing an embodiment in which a magnetic field is applied to the superconducting magnetoresistive element using a permanent magnet. In FIG. 10, 101 is an element, 102 and 103 are terminals, and 104 is a permanent magnet.

In the embodiment shown in FIG. 10 described above, a sensitive displacement sensor can be constructed by using the permanent magnet 104 having a constant strength and movably providing the permanent magnet 104 with respect to the element 101. That is, since the electric resistance of the element 101 changes abruptly as shown in FIG. 11 due to the change in the relative distance (d or l) between the magnet 104 and the element 101, the change in the electric resistance causes the magnet for the element 101 to move. 104 displacements can be measured.

FIG. 12 is a diagram showing another embodiment of the present invention, in which the electrode 123 is also provided in the central portion of the superconducting magnetoresistive element 121, and a magnetic field is applied to a part of the element having three terminals, By moving this magnetic field along the element 121, the resistance ratio in the element 121 is changed to form a potentiometer, 121 is a superconducting magnetoresistive element, and 122 and 124 are elements 1.
Constant current input first and second electrodes provided at both ends of 21; 123, an output voltage detection third electrode provided at the center of the element 121; and 125, a weakly coupled element 121. Means (permanent magnet) for applying a magnetic field larger than the magnetic field (critical magnetic field) that breaks the superconducting state, and is provided so as to be movable along the element 121.

In the above configuration, when a value larger than the critical magnetic field is applied between the electrodes 122 and 123 of the three-terminal element 121 by the permanent magnet 125, the superconducting state is broken between the electrodes 122 and 123, and the electric resistance that appears between the electrodes 122 and 123 appears. R ₂₃ has a finite value. In this case, the magnetic field is not applied to the superconductor between the electrodes 123 and 124, and therefore, the superconducting state is shown,
The resistance R ₃₄ between the electrodes 123 and 124 is zero.

Therefore, even if the input voltage V _in is applied between the electrodes 122 and 124,
The output voltage V _out between the electrodes 123 and 124 is zero.

Next, the magnetic field 125 is moved to a position on the electrode 123. At this time, when the areas of the magnetic fields applied to the superconductor between the electrodes 122 and 123 and between the electrodes 123 and 124 are almost equal, the resistance R ₂₃ between the electrodes 122 and 123 and the resistance R ₃₄ between the electrodes 123 and 124 are both about half of the superconductivity. The state is broken and the resistance becomes R ₂₃ = R ₃₄ .

Therefore, the voltage appearing between the electrodes 123 and 124 is V _out = 1 / 2V _in
Becomes half of the input voltage.

Further, when the position of the magnetic field 125 is moved between the electrodes 123 and 124, the magnetic field is applied only between the electrodes 123 and 124, and the superconductor between the electrodes 122 and 123 is in the superconducting state, so that the resistance R ₂₃ = 0 and the superconducting state between the electrodes 123 and 124 becomes When broken, the electric resistance R ₃₄ appearing between the electrodes 123 and 124 has a finite value.

Therefore, the output voltage appearing between the electrodes 123 and 124 is V _out = V
become _in equal to the input voltage.

The relationship between the displacement of the magnetic field and the output voltage explained above is as follows if the displacement position of the magnetic field 125 from the electrode 122 side of the superconductor is l.
As shown in FIG. 13, the output voltage V _out changes linearly (corresponding to the displacement 1 of the magnetic field 125) from zero to the input voltage V _in , and a contactless potentiometer can be realized.

Further, the output characteristics shown in FIG. 13 above obtain logarithmic or paper number functions and any other desired characteristics by using elements in which each cross-sectional shape in the displacement direction of the magnetic field of the element 121 is sequentially changed. You can

In the above potentiometer, since the magnet 125 and the element 121 are not in contact with each other, noise is not generated and an excellent reliability is obtained.

Further, in the above example, although the superconducting element 121 is linear, it has an element shape in which the superconductor is arranged on the circumference, and by arranging the magnetic field applying means 125 to move concentrically, It is possible to obtain characteristics similar to those of a normal rotary potentiometer.

FIG. 14 is a diagram showing an embodiment in which a magnetic field is applied to the superconducting magnetoresistive element 141 by using an electromagnet. In FIG. 14, 141 is an element, 142 and 148 are electrode terminals, and 144 is an electromagnet.

In the embodiment shown in FIG. 14, the magnetic field B acts on the element 141 by causing a predetermined current to flow through the coil of the electromagnet 144, and the resistance value between the electrode terminals 142 and 143 of the element 141 greatly changes. That is, when no current is flowing in the coil of the electromagnet 144, the element 141 maintains the superconducting state, so the resistance between the electrode terminals 142 and 143 of the element 141 is zero, but a current is caused to flow in the coil of the electromagnet 144 to generate it. When the magnetic field B is applied to the element 141, the element 141 exhibits a large electric resistance.

Therefore, the magnetoresistive device having the above structure can be used as a kind of electromagnetic relay, for example, by connecting it in series with a load and a power supply, or by connecting to a control terminal of a high input impedance element such as a MOS transistor.

The above magnetoresistive device may be configured such that, for example, as shown in FIG. 15, a superconducting magnetoresistive element 151 having electrode terminals 152 and 153 is disposed inside a coiled solenoid 154, and a sixteenth As shown in the figure, a superconducting magnetoresistive element 1 having electrode terminals 162 and 163 in the void portion of a substantially donut-shaped electromagnet 164 in which a coil 165 is wound and a void is provided by partially cutting it out.
Even if 61 is arranged, it can be used as a kind of electromagnetic relay in the same manner.

When the electromagnetic relay is configured as described above, it does not cause a vibration phenomenon such as chattering, which is a drawback of conventional electromagnetic relays, so it can be opened and closed precisely, and contact failure due to dust, oxidation, etc. There is no occurrence of noise, and no noise or mechanical noise is generated during operation.

The magnetoresistive device shown in FIG. 14 has the electromagnet 144 and the element 1
Since the electric resistance of the element 141 changes according to the relative displacement with respect to 41, it can be used as a displacement sensor or a position sensor as in the element system shown in FIG.

Further, in the magnetoresistive device shown in FIGS. 10 and 14 to 16 described above, the resistance value of the element is arbitrarily changed by the relative displacement of the permanent magnet, the electromagnet and the element, or the magnitude of the current flowing in the electromagnet. Therefore, each of the magnetoresistive devices can be used as a contactless variable resistor.

FIG. 17 is a diagram showing the configuration of another embodiment of the present invention, showing an example in which a superconducting magnetoresistive element is applied to microwaves.

In FIG. 17, reference numeral 171 is a microwave waveguide, and a superconducting magnetoresistive element (superconducting film) 172 is located in (for example, an inner wall of) the waveguide 171, and an electromagnet 173 or the like provided outside the element 172. The magnetic field B is made to act by the.

In the above structure, when the magnetic field B is not applied to the element 172, the superconducting magnetoresistive element 172 has a resistivity of zero and no loss, so that the microwave propagates without being attenuated at all.

Next, when a magnetic field B is applied to the superconducting magnetoresistive element 172 in the waveguide 171 from the outside by an electromagnet 153 or a permanent magnet,
Since the superconducting state of the element 172 is broken and the element 172 exhibits electric resistance, the microwave propagating in the waveguide 171 is absorbed and attenuated to some extent by the element 172. When the strength of the magnetic field B applied to the element 172 is increased, the attenuation of microwaves is also increased as shown in FIG. 18, and the magnetoresistive device shown in FIG. 17 has a mechanical structure. It functions as a variable attenuator for microwaves that does not accompany it.

FIGS. 19 (a) and 19 (b) are diagrams showing other embodiments when the present invention is applied to microwaves.

In FIGS. 19A and 19B, reference numeral 191 is a microwave waveguide, and electrode terminals 192 and 193 are provided at the center of the waveguide 91.
A superconducting magnetoresistive element 194 having the above is attached in a post shape, and electrode terminals 192 and 193 are connected to the inner wall of the waveguide 191, respectively.

In the above structure, as shown in FIG. 19 (a), when the magnetic field B is not applied to the element 194, the element 194 is in the superconducting state and has a resistance value of zero. This element 1 as well as a metal post in tube 191
The microwave electric field becomes zero at the 94th part, and for example, the waveguide 19
Microwaves incident from the left side of 1 are reflected by the waveguide 191
Is not propagated to the right side of.

Next, as shown in FIG. 19 (b), when a magnetic field B is applied to the element 194, the superconducting state of the element 194 is broken, the element 194 becomes a resistor, and the microwave is only partially absorbed. Is propagated in the direction.

Therefore, the magnetoresistive device shown in FIGS. 19A and 19B acts as a microwave switch by the magnetic field.

Further, in the configuration shown in FIG. 19 (b), the amount of passing microwaves changes by changing the strength of the magnetic field B, so that it can also be used as a variable attenuator of microwaves.

FIG. 20 is a perspective view showing the configuration of another embodiment of the present invention, and shows an example in which the magnetoresistive device of the present invention is used in a magnetic field detection device.

In FIG. 20, 201 is a superconducting magnetoresistive element, and the element 201 is provided with current electrodes 202, 202 and voltage electrodes 203, 203.

A magnetic field slightly larger than the magnetic field (critical magnetic field) in which the weak coupling state of superconductivity is broken beforehand by the permanent magnet 204 or the like is applied to the element 201 as the bias magnetic field B ₀ , and the magnetic field B of the weak magnetic field signal source 205 to be detected is detected. _S is superimposed and applied to the element 201.

In the above configuration, while maintaining the element 201 at a temperature below the critical temperature indicating a superconducting state, the current terminals 202, 202
When a current of 100 mA is applied through the element, as described above, in the element having the characteristics shown in FIG. 6, the element 201 maintains the superconducting state up to the magnetic field of 5 gauss, and when the magnetic field exceeds 5 gauss, the superconductivity is weak. The binding state is broken to show electric resistance, and this characteristic has a steep slope as shown in FIG.

Therefore, the magnetic field in the region showing the steep slope of this characteristic,
For example, a magnetic field of 20 gauss is applied to the element 201 in advance as a bias magnetic field B ₀ , and a weak signal magnetic field B _S is superposed on the bias magnetic field B ₀ , and this signal magnetic field B _S is used as a resistance change ΔR of the element 201. It becomes possible to detect, and the change of the signal magnetic field B _S is detected as a voltage change from the voltage terminals 203, 203.

In the above embodiment, the element 201 operates with the position of the bias magnetic field B ₀ having a large rate of change as the operating point, as shown by the dotted line in FIG. 21, in which the weakly coupled superconducting state is broken. For this reason,
The electric resistance changes greatly with a slight change in the signal magnetic field.

Further, the electric resistance value of the element 201 can be controlled by the shape of the element. For example, as shown in FIG. 22, a region where the element becomes superconducting is formed in a zigzag shape by fine processing.
It was set to 1KΩ by setting 221. in this case,
Element 201 is approximately 270 mΩ for a change in the signal magnetic field of 1 Gauss
It changed and produced an output voltage of 27 mV for a current of 100 mA.

Incidentally, as a method for increasing the resistance of the element by processing it into the zigzag shape shown in FIG. 22, for example, the surface of the element is subjected to ion implantation treatment or laser irradiation treatment to erase the superconducting characteristic of that portion. It is possible to form a zigzag shape as described above, and the above-mentioned high resistance is not limited to the embodiment shown in FIG. It goes without saying that it is possible to increase the values such as.

Further, in the embodiment shown in FIG. 20, in order to easily adjust the detection sensitivity, the bias magnetic field is generated by using an electromagnet, and the bias magnetic field value is controlled by controlling the exciting current. It may be controlled.

In each of the embodiments of the magnetoresistive device of the present invention described above, all the elements made of a material exhibiting a complete superconducting state have been described, but the present invention is not limited to this, for example, an oxide. Due to the composition of the ceramic, as shown in FIG. 23, when the applied magnetic field is zero, there is a very small resistance value R ₀ , but there are some which show a markedly sharp resistance with an increase in the applied magnetic field. The principle is exactly the same in the case of an element using such a material, and even if such an element is used, a similar magnetoresistive device can be configured and a similar effect can be obtained.

An example of manufacturing an element having the characteristics shown in FIG. 23 is shown below.

Y _1.2 Ba _1.8 Cu ₃ O _7-x superconductor was obtained by weighing out a predetermined amount of yttrium oxide Y ₂ O ₃ , barium carbonate BaCO ₃ , and copper oxide CuO to obtain fine particles sufficiently dispersed and mixed at 900 ° C. No calcination in air for a period of time, then pulverize and disperse again to make powder consisting of uniform fine particles (1 μmφ or less), and make circular pellets at a pressing force of 1 ton / cm ² , then 1000 ℃,
It was calcined in air for 3 hours and cooled to 200 ° C. in 5 hours to prepare circular pellets having a thickness of 1 mm.

The superconducting material produced as described above is composed of many superconducting particles, and there is an extremely thin insulator or resistor at the grain boundary, and although there are weakly bonded ones with different critical temperatures, the whole Can be regarded as a weakly coupled aggregate of superconductors, similar to the structure shown in FIG.

When a magnetic field is not applied, the superconducting material produced as described above begins to sharply decrease its electric resistance at an absolute temperature of 82 degrees as shown in FIG. 24, and has an extremely small electric resistance at an absolute temperature of 78 degrees. (R ₀ = 12 mΩ), and the electrical resistance became completely zero at an absolute temperature of 38 degrees.

After cutting out the element piece from the above material and attaching the electrode, put the element in liquid nitrogen (77K) and measure the resistance of the element by passing a constant current (5 mA) through the electrode,
When no magnetic field is applied, the resistance of the element remains as an extremely small value (R ₀ = 12 mΩ), but when applied,
The resistance of the device increased rapidly with the increase of the magnetic field, and the characteristics shown in FIG. 23 were exhibited.

Although the magnetoresistive device as the above-mentioned embodiment of the present invention was constructed using the element having such characteristics, the element made of the superconducting material having a resistance value of completely zero when no magnetic field was applied was used. It was confirmed that an operation result similar to that in the case was obtained, and that there was no problem in practical use.

Further, when such an element is used, higher resistance is achieved as compared with those of the other examples shown above, and particularly in the system control required as a large voltage change due to resistance change. It is more preferable to use this element.

Since the superconducting magnetoresistive element used in each of the above examples is in a superconducting state at or near an absolute temperature of 80 degrees, it should be cooled by using an electronic cooling element such as liquid nitrogen or a Peltier cooling element. However, it goes without saying that an element that becomes superconducting or close to it at room temperature can be put to practical use without cooling.

In addition, in the said Example, although Y-Ba-Cu-O type | system | group was demonstrated as an example as a superconducting ceramic, this invention is not limited to this, For example, La-Ba-Cu-O type | system | group,
Group IIIa element, group IIa element, copper (Cu) element and oxygen (O) element such as Y-Sr-Ba-Cu-O system, or part of oxygen (O) element substituted with fluorine (F) element The same operation can be performed by using a superconducting ceramic having a constituent element of or a polycrystalline superconducting material having other grain boundaries.

Further, although the sintering method has been described as an example of the method for producing the superconducting material, the present invention is not limited to this, and a melting method, a thin film producing method (a sputtering method, a vapor deposition method, etc.), a thick film It goes without saying that it may be manufactured using a manufacturing method (spray method, screen method, doctor blade method, etc.).

In short, the present invention is a polycrystalline body composed of many superconductor fine particles, in which an extremely thin insulator or resistor is present at the grain boundary, or the contact portion between grains becomes point-like, that is, grain boundaries. And the grain boundaries are in a point-like contact with each other, or in a so-called weak superconducting state or in a state close thereto, and this state is broken by the application of a magnetic field, as shown in FIG. 1 or FIG. It goes without saying that any material can be used as long as it is an element material exhibiting characteristics.

<Effects of the Invention> As described above, according to the present invention, by utilizing the weak coupling between the superconducting particles constituting the ceramic superconductor,
It is possible to provide a superconducting magnetoresistive device that exhibits a high-performance resistance change even with a weak magnetic field by performing an action based on a novel phenomenon different from the conventional magnetoresistive element. That is, in the conventional magnetoresistive element using a semiconductor, the resistance increase ΔR with respect to a weak magnetic field of, for example, several tens of gauss is extremely weak, and the resistance increase ΔR with respect to the resistance R ₀ when no magnetic field is applied is
The value of R / R ₀ was at most about 1%, but in the superconducting magnetoresistive device of the present invention, R ₀ is completely zero even for a very weak magnetic field of several to several tens Gauss, and therefore ΔR The value of / R ₀ becomes infinite, and it is possible to realize a high-performance magnetoresistive device that is not comparable to conventional magnetoresistive elements.

Furthermore, according to the present invention, since the ceramic superconductor is composed of the weak coupling between the superconducting particles, the CW
Chu et al. Phys. Rev. Lett. 58 [4] (26 Jan. 198
7) The structure of the material itself is different from that of the multiphase La-Ba-Cu-O compound-based superconducting material containing the K ₂ NiF ₄ phase as shown in the document of pp.405-407. The principle of changing the resistance is also different. Therefore, in the above-mentioned document, the change in the electric resistance due to the superconducting phenomenon is observed only in the state where a very strong magnetic field of 4.5 k Gauss or more is applied, but in the present invention, a very weak magnetic field of several to several tens Gauss is observed. On the other hand, it is possible to realize a high-performance superconducting magnetoresistive device that can exhibit a resistance change with high performance and cannot be predicted from the above literature.

As described above, according to the present invention, it is possible to configure devices such as a magnetic sensor for detecting a weak magnetic field with high sensitivity, a magnetic head, a non-contact potentiometer, a variable resistor, and a microphone wave attenuator, and It can be widely used as an application to control devices in energy systems, transportation systems, etc. using superconductivity.

[Brief description of drawings]

FIG. 1 is a diagram showing characteristics of a ceramic superconducting magnetoresistive element in one embodiment of the present invention, FIG. 2 is a diagram schematically showing a structure of a ceramic superconducting material, and FIG. 3 is an equivalent circuit of a ceramic superconductor. 4 and FIG. 4 are diagrams showing electric resistance characteristics with respect to temperature of a superconducting material, FIG. 5 is a diagram showing one structural example of a magnetoresistive device in one embodiment of the present invention, and FIG. The figure which shows an example of the characteristic which showed the resistance change with respect to the magnetic field of the element used as the parameter which made the electric current flow into an element, FIG. 7 is a figure which shows the basic composition of the superconducting magnetoresistive element used in the Example of this invention, FIG. FIG. 9 is a diagram showing another example of the characteristics in which the resistance change with respect to the magnetic field of the element used in the embodiment of the present invention is shown as a parameter, and FIG. 9 is the resistance of the element used in the embodiment of the present invention. Shows a magnetic field threshold of appearance of,
FIG. 10 is a diagram showing an embodiment in which a magnetic field is applied to the element by using a permanent magnet, FIG. 11 is a diagram showing characteristics of the magnetoresistive device shown in FIG. 10, and FIG. 12 is an embodiment of the present invention. As a diagram showing the basic structure of a superconducting contactless potentiometer, FIG. 13 is a characteristic diagram showing the relationship of the output voltage with respect to the magnetic field change of the magnetoresistive device shown in FIG. 12, and FIGS. FIG. 17 is a diagram showing an embodiment in the case of applying a magnetic field using an electromagnet, FIG. 17 is a diagram showing the configuration of another embodiment of the present invention when applied to a microwave, and FIG. 18 is a magnetic diagram shown in FIG. FIG. 19 is a diagram showing the characteristics of the resistance device, FIGS. 19 (a) and 19 (b) are diagrams showing the configuration of another embodiment when applied to microwaves, and FIG. 20 is a magnetic field detection of the magnetoresistance device of the present invention. FIG. 21 is a diagram showing an embodiment when used in a device, and FIG. 21 explains the operation of the magnetoresistive device shown in FIG. FIG. 22 is a diagram showing an example when the element shape used in the embodiment of the present invention is a zigzag shape, and FIG. 23 is another example of characteristics of the element used in the embodiment of the present invention. Showing the 24th
FIG. 25 is a diagram showing another example of the electric resistance characteristic of the superconducting material with respect to temperature, and FIG. 25 is a diagram showing the characteristic of the conventional magnetoresistive element. 1 ... Superconducting fine particles, 2 ... Particle boundaries, 3 ... Josephson junction, 51,71 ... Superconducting magnetoresistive element, 52, 53 ...
Electrodes, 56 ... magnetic field, 72 ... current electrode, 73 ... voltage electrode.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-59-17175 (JP, A) JP-B-48-28598 (JP, B1) Phys. Rev. Lett. 58 [4] (26 Jan. 1987) PP. 405-407

Claims (11)

[Claims] 1. An element made of a ceramic superconducting material having a large number of crystal grain boundaries, in which crystal grains exhibiting superconductivity are electrically weakly coupled to each other, a means for applying a magnetic field to the element, and A means for utilizing a change in electric resistance that occurs when a magnetic field is applied, and a superconducting magnetoresistive device. 2. The superconducting magnetoresistive device according to claim 1, wherein the element made of the superconducting material is a two-terminal element. 3. The superconducting magnetoresistive device according to claim 1, wherein the element made of the superconducting material is a three-terminal element. 4. The superconducting magnetoresistive device according to claim 1, wherein the element made of the superconducting material is a four-terminal element. 5. The superconducting magnetoresistive device according to claim 1, wherein the means for applying the magnetic field is a permanent magnet. 6. The superconducting magnetoresistive device according to claim 1, wherein the means for applying the magnetic field is an electromagnet. 7. The superconducting magnetoresistive device according to claim 5, wherein the permanent magnet is provided so as to be movable relative to the element. 8. The superconducting magnetoresistive device according to claim 6, wherein the electromagnet is provided so as to be movable relative to the element. 9. The superconducting magnetoresistive device according to claim 1, wherein the means for applying the magnetic field is means for applying a bias magnetic field and a signal magnetic field. 10. The superconducting magnetoresistive device according to claim 1, wherein the means for utilizing the change in the electric resistance includes means for applying a microwave to the element. 11. The superconducting magnetoresistive device according to claim 1, wherein the means for utilizing the change in the electric resistance includes means for detecting the change in the electric resistance as a voltage change.