JPH0672914B2 - Driving method for superconducting magnetoresistive element - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for driving a superconducting magnetoresistive element that reduces the influence of a noise magnetic field by driving a superconducting magnetoresistive element having a folded back and non-inductive structure with an alternating current or the like. It is a thing.

<Prior Art> Conventionally, a magnetoresistive element using a magnetic material has been used. In addition, we recently announced a ceramic superconductor magnetoresistive element that has high sensitivity to a relatively weak magnetic field due to the characteristics of grain boundaries. This superconductor magnetoresistive element breaks the superconducting state of the grain boundaries of the superconductor particles by the applied magnetic field and has a resistance of normal conduction, and shows a rapid increase in resistance to a weak applied magnetic field.

<Problems to be Solved by the Invention> A conventional magnetoresistive element using a magnetic material changes the resistance value of the element due to the interaction between a magnetic field and a current applied to the element, and no magnetic field is applied. At that time, there was a defect that the element had resistance and the increase in resistance when the applied magnetic field was weak was very small. Also, it had directivity with respect to the applied magnetic field. In order to improve this, the shape and drive circuit of the previously announced ceramic superconducting magnetoresistive element is the third.
It looked like the figure. In FIG. 3, a ceramic superconducting magnetoresistive element 9 is provided with a pair of current electrodes 3 and voltage electrodes 4 on an elongated body 1. The current electrode is a DC power supply 7, and the voltage electrode 4 is a voltmeter 8. It is connected to the.

As shown in FIG. 3, the power supply and the voltage detection circuit are connected to change the applied current I and applied magnetic field H, and the relationship between the strength of the applied magnetic field and the resistance R between the voltage electrodes of the superconducting magnetoresistive element 9 for each applied current. Is shown in FIG. As can be seen from FIG. 4, by increasing the distance between the electrodes of the superconducting magnetoresistive element 9 or decreasing the cross-sectional area thereof, it is possible to increase the change in the element resistance corresponding to the change in the applied magnetic field H. ,
It is impossible to drive the element 9 with an alternating current or a modulated current because the resistance generated in the element 9 varies depending on the magnitude of the applied current I.

The present invention provides a method for driving a superconducting magnetoresistive element, which solves the above problems that the conventional magnetoresistive element has, and which has a high sensitivity and which increases the S / N ratio by AC driving or the like. Is.

<Means for solving the problem> Using a superconductor having a high critical temperature (Tc) such as a ceramic superconductor having a magnetoresistive effect to form a thin film, or
Even if the film is made thicker and the size is smaller, the current flowing with high precision will be reversed. However, it was found that the resistance characteristics of the element generated by the magnetic field did not change. Therefore, the present invention can obtain a voltage output proportional to the intensity of the applied current from the magnetoresistive element, even if an alternating current, or a pulse or any other current having a modulated waveform is applied to the element. ,
By the method of obtaining the voltage output synchronized with the modulation current, it is possible to detect and measure a very small magnetic field with extremely high sensitivity as compared with the conventional magnetoresistive element of ceramic superconductor without being affected by noise and drift. Be the way.

<Operation> Superconducting magnetoresistive elements, which have high magnetic sensitivity due to grain boundaries such as ceramics, even when the strength of the magnetic field to be measured was constant, the resistance generated in the element also increased when the current passed through the element increased. This is because it is related to the generation of the resistance of the element of the magnetic field created by the current flowing through the element.
If currents of the same magnitude are connected so that they flow in opposite directions to the superconducting magnetoresistive elements that form a pair of adjacent linear elements, the magnetic fields generated by the elements cancel each other out,
Since the element is not affected by the magnetic field due to the current, the element has a constant resistance to the magnitude of the magnetic field regardless of the magnitude of the current. Therefore, it is possible to measure the magnetic field by passing an alternating current or an arbitrarily modulated current through the element, detecting the element voltage in synchronization with the current.

<Example> An example of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, in which a superconductor film 1 is formed on a substrate (not shown) so as to form a Y-Ba-Cu-O ceramic superconductor, a nitrate of its constituent elements. Was prepared as an aqueous solution by a spray pyrolysis method and heat-treated in an oxygen atmosphere to adjust the oxygen composition ratio. The ceramic superconducting magnetoresistive element 9 having a folded structure was formed by removing the superconductor portion of the insulating portion 2 of the produced film. This element has an outer shape of about 5 × 10 mm and a superconductor film thickness of about 10 μm.
Met.

In this embodiment, a Y-Ba-Cu-O ceramic superconductor is used for the superconductor film 1, but other superconductors may be used, and the film may be formed by sputtering or CVD. Titanium (Ti) was added to the manufactured magnetoresistive element 9.
Current electrode 3 and voltage electrode 4 by vapor deposition or silver paste
Were connected to a current source 5 for flowing a current I to the element 9 and a voltmeter 6 for measuring the voltage generated in the element. FIG. 2 is a graph showing a representative example of the characteristics produced and measured as described above. The critical temperature (Tc) of the superconductor used was about 90 K, and the temperature was liquid nitrogen temperature (77 K). In this figure, the vertical axis represents the resistance value generated in the element 9, and the horizontal axis represents the strength of the applied magnetic field.

As can be seen from the characteristics of the element 9 shown in FIG. 2, its resistance value shows stable characteristics that do not depend on the current flowing through the element at all, and the resistance value is always constant depending on the strength of the magnetic field to be measured applied from the outside. Was occurring.

The current value outside the measurement range in FIG. 2 and the alternating current were also measured, but the resistance values in this figure were obtained.

<Effects of the Invention> In the present invention, the alternating current or other modulation current is applied to the superconducting magnetoresistive element of the non-inductive configuration, which is composed of the pair of linearly folded wires and whose current directions are opposite to each other. Since it is applied, it has characteristics of a superconductor that is sensitive to a magnetic field, and the generated resistance value does not change depending on the magnitude of the flowing current. Therefore, the AC, pulse current or other modulation applied to the element It will be possible to detect the voltage output in synchronization with the current, or to synchronously amplify,
Weak magnetic field S / N ratio can be measured with high accuracy.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a characteristic view of the embodiment of FIG. 1, FIG. 3 is a perspective view of an embodiment of a conventional element, and FIG. 4 is a view of FIG. It is a characteristic diagram. 1 is a superconductor film, 2 is an insulating part, 3 is a current electrode, 4 is a voltage electrode, 5 is a current source, 6 is a voltmeter, 7 is a DC power supply, 8 is a DC voltmeter, 9 is a magnetoresistive element, and 10 is a magnetic field. Is.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-59-17175 (JP, A) Actually opened 58-56980 (JP, U) Actually opened 58-56981 (JP, U) Actual-public Sho-57- 2891 (JP, Y2) S. 56-3610 (JP, Y2) C.I. W. Chu, st al. , Physical Review Letters, Vol. 58, No. 4, PP. 405-407 (1987)

Claims (1)

[Claims] 1. An alternating current or other modulation current is applied to a current terminal of a superconducting magnetoresistive element of a non-inductive structure, which is composed of a pair of linearly folded wires and whose current directions are opposite to each other. A method for driving a superconducting magnetoresistive element, characterized in that the voltage output generated by the element is detected in synchronization with the applied current.