JPH03259762A - Instrument for measuring superconducting properties - Google Patents

Abstract

PURPOSE:To make exact measurement by housing a 2nd cooling tank disposed with a superconductor sample into the inside hole of a 1st cooling tank provided with a coil for impressing AC magnetic fields, thereby maintaining the coil for impressing the AC magnetic fields at a specified temp. during measurement. CONSTITUTION:The toric coil 28 for impressing the AC magnetic fields is provided into the 1st cooling tank 27 of a cylindrical shape provided on a cold stage 24 of a 1st cryogenic refrigerator 20. The superconductor sample 45 is disposed in the 2nd cooling tank 43 provided on a cold stage 34 of a 2nd cryogenic refrigerator 30. The cooling tank 43 is housed in the inside hole of the cooling tank 27 and while the coil 28 is held at the specified temp., the temp. of the superconductor sample 45 is changed by the refrigerator 20. The coil 28 is held at the specified temp. by the refrigerator 20 during the measurement in this way and, therefore, background noises are removed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a superconducting physical property measuring device, and particularly to a measuring device for alternating current magnetic susceptibility of a superconductor.

(Prior Art) A cryogenic refrigerator uses a Stirling cycle or a Gibbord-McMapon (GM) cycle to obtain a cryogenic temperature of 100 degrees or less. On the other hand, when a certain substance is cooled to an extremely low temperature, its electrical resistance becomes zero. In other words, it is a superconducting material, but in general, to determine whether or not the material exhibits superconducting physical properties,
It is necessary to confirm the crystal structure, confirm the Meissner effect, confirm that electrical resistance suddenly disappears near the transition point, and confirm the reproducibility of test results.

The Meissner effect (complete rebelliousness of a superconductor, which is the opposite of iron in a magnetic field, is used to confirm whether or not a superconductor exhibits physical properties).In reality, when a magnetic field is applied to a superconductor from the outside, the magnetic field completely changes to make it superconducting. It is not excluded to the outside of the body, but the magnetic field penetrates only a slightly thin layer on the surface, and an electric current flows through this thin layer.

That is, it becomes magnetized. Furthermore, unless the sample is a perfect superconducting crystal, the sample will contain non-superconducting parts, and the degree of magnetic field rejection will differ. ) can be measured using the alternating current method and the direct current method (
SQUID magnetic susceptibility meter).

(1) (2) The AC method according to the present invention involves placing a sample in a coil wound around an annular bobbin for detecting signals from a superconductor sample (hereinafter simply referred to as the sample) while an AC magnetic field is applied. , which captures changes in the magnetic susceptibility of a sample as changes in coil inductance and loss, and obtains information about the Meissner current inside the material.

A measuring device using the AC method will be briefly explained with reference to FIG. The cryogenic refrigerator 1 transmits cryogenic temperature to the measurement head 5 via the cold stage 4 in the vacuum chamber 3 in the shield case 2. The measurement head 5 is located in a cooling tank 7 formed by an inner case 6, and consists of an annular bobbin 8 and an alternating current magnetic field application coil 9 wound around the bobbin 8.
A sample 10 is placed within the hollow space. Reference numeral 11 is an internal wiring for passing current through the coil 9, and reference numeral 12 is a terminal for receiving data from the sample 10. A dummy sample 13 is arranged at a position apart from the measurement head 5, and a temperature signal from this dummy sample 13 is taken out to the outside. In the figure, 14 is a temperature measuring resistor of the cold stage 4.

(Problems to be Solved by the Invention) When magnetic susceptibility is measured using the conventional measuring device described above, as shown in Figure 5, the background slope is large before the critical temperature (TO) at which superconductivity occurs, and after Tc. This trend can also be seen.

This is because in conventional equipment, the coil itself is cooled at the same time as the sample, so the resistance of the coil decreases, and even if the applied voltage at each temperature is constant, the applied current and applied magnetic field of the coil will change. This is because the magnetic susceptibility data overlaps with the magnetic susceptibility data as a hack ground, and as a result, there is a problem in that the conventional apparatus cannot perform accurate measurements.

Therefore, the technical problem of the present invention is to maintain the alternating current magnetic field applying coil at a constant temperature during measurement, eliminate the above-mentioned background slope, and enable accurate measurement of superconducting physical properties.

[Structure of the invention]

(Means to solve the problem) The measures taken to solve the above technical problem are the first
An annular alternating current magnetic field applying coil is disposed in the cylindrical first cooling tank installed on the cold stage of the cryogenic refrigerator (3) (4), and a cold stage of the second cryogenic refrigerator is installed. A superconductor sample is placed in a second cooling tank provided on a stage, the second cooling tank is accommodated in the inner hole of the first cooling tank, and the alternating current magnetic field applying coil is connected to the first pole. The temperature of the superconductor sample is changed by the second cryogenic refrigerator while maintaining the temperature at a constant temperature by a low-temperature refrigerator.

(Function) According to this, since the AC magnetic field applying coil can be maintained at a constant temperature during measurement by the first cryogenic refrigerator,
The background noise mentioned above can be removed,
Accurate measurements of superconducting physical properties can be made. Incidentally, according to the apparatus of the present invention, magnetic susceptibility data shown in FIG. 3 can be obtained.

(Example) Hereinafter, one example of the superconducting physical property measuring device according to the present invention will be described based on the drawings.

In FIG. 1, 20 is a two-stage first cryogenic refrigerator equipped with a first-stage freezing section 21 and a second-stage freezing section 22. Radiation shield plate 2
3 is provided, and a cold stage 24 is provided in the second stage freezing section 22. The first cryogenic refrigerator 2o is fixed to a base member 29 and guide members 30a and 30b that are erected on the base member 29 in parallel to the axis of each of the freezing sections 21 and 22.

The cold stage 24 is provided with an M-shaped cover 25, as shown in FIG. One end of the cover 25 is fixed to the cold stage 24, and one end of the cover 25 is fixed to the cold stage 24.
A bottomed bobbin 26 is fixed to the other end. As a result, a cylindrical first cooling tank 27 filled with He gas or the like is formed above the cold head 24. An alternating current magnetic field applying coil 28 wound around the outer periphery of the bobbin 26 is disposed within the first cooling tank 27 . Incidentally, the alternating current magnetic field applying coil 28 is configured to receive current from a power source (not shown).

On the coaxial line of each freezing section of the first cryogenic refrigerator 20 (5) (6), two
A second stage cryogenic refrigerator 30 is provided. A radiation shield that surrounds the first stage freezing section 31 and the second stage freezing section 32.
A plate 33 is provided, and a cold stage 24 is provided in the second stage freezing section 22. The second cryogenic refrigerator 30 is fixed to slider parts H35 and 36 that are slidably disposed on guide members 30a and 30b,
At its lowest position, the slider member 35 is at the kite portion +A'
30a is defined by coming into contact with a flange 37 provided at the flange 37a. In addition, in the second cryogenic freezing @ 30, by increasing or decreasing the weight of the balance T') eight 41 connected to the slider member 36 via the wire 42, the guide member can be passed through the pulleys 39 and 40 provided on the support column 38. 3
It moves up and down along 0a and 30b, and at its lowest position, the openings of both radiation shield plates 2333 overlap.

A cover 44 is fixed to the cold stage 34 of the second cryogenic refrigerator 30, and the cover 44 forms a second cooling tank 43 filled with l(e gas, etc.). ”A superconductor sample 45 is arranged.This cover 4
4B, Bohin 2 at the lowest position of the second cryogenic refrigerator 30
According to the superconducting physical property measuring device having the above configuration, the inner hole 26a of No. 6 has an intersection? The temperature of the magnetic field applying coil 28 is maintained at a constant temperature by the first cryocooler 20 and a constant magnetic field is always created with respect to the applied voltage. Only the temperature of the body sample 45 can be changed. Therefore, according to the measuring device according to this embodiment, more accurate magnetic susceptibility data as shown in the third article can be obtained.

〔Effect of the invention〕

According to the present invention, accurate magnetic susceptibility data that depends on the strength of the magnetic field can be obtained. Furthermore, since the sample temperature and coil temperature can be easily controlled and maintained using respective cryogenic refrigerators, reliable data with high reproducibility can be obtained.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of the superconducting physical property measuring device according to the present invention, FIG. 2 is an enlarged cross-sectional view of the measuring section (7) (8) in FIG. 1, and FIG. A graph of magnetic susceptibility data, FIG. 4 is a cross-sectional view of the conventional example, and FIG. 5 is a graph of magnetic susceptibility data in the conventional example. 20... First cryogenic refrigerator, 24... Cole I-stage, 25... Cover, 26... Bohin, 27...
...First cooling tank, 28...AC'/N, magnetic field application coil, 30...Second cryogenic refrigerator, 34...Cold" stage, 43...Second cooling tank, 44 ...Cover, 45...Superconductor sample.

Claims (1)

[Claims] An annular alternating current magnetic field applying coil is disposed in a cylindrical first cooling tank provided on the cold stage of the first cryogenic refrigerator, and a coil for applying an alternating current magnetic field is provided on the cold stage of the second cryogenic refrigerator. A superconductor sample is disposed in a second cooling tank, the second cooling tank is accommodated in the inner hole of the first cooling tank, and the alternating current magnetic field applying coil is heated at a constant temperature by the first cryogenic refrigerator. An apparatus for measuring superconducting physical properties, characterized in that the temperature of the superconductor sample is changed by the second cryogenic refrigerator while maintaining the superconductor sample at a temperature of .