JPH0335182A - Instrument for measuring superconducting magnetic field - Google Patents

Abstract

PURPOSE:To make efficient measurement with high accuracy by measuring an external magnetic field by the output signal generated by the impression of the AC bias magnetic field from a superconducting magneto-resistance element. CONSTITUTION:The waveforms of the AC output b of the superconducting magneto-resistance element 14 generated in accordance with the DC bias mag netic field are a, b, c, d, e, f when a prescribed current is passed to a coil 16 in the state of passing an AC current to a coil 15 and the DC bias magnetic field to attain points A, B, C, D, E is impressed thereto. This output signal and the AC magnetic field generating signal are inputted to a lock-in amplifier, which extracts the narrow band of only 1KHz. The effective value of noises is kept low in this way and even the slightest magnetic field is measured with a high resolving power.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention utilizes the magnetoresistive effect of a superconductor having weak coupling at grain boundaries to measure a magnetic field by applying a bias magnetic field. It concerns a measurement method that utilizes a high sensitivity range.

<Prior Art> Conventionally, magnetoresistive elements using semiconductors or magnetic materials have been generally used for detecting and measuring magnetic fields. InSb is a semiconductor with particularly high electron mobility.

Shape effect in InAs etc. 9 Fe-N which is a ferromagnetic metal
Elements using the orientation effect of %Co-Ni and the like have been put into practical use.

Additionally, methods have been developed to detect and measure weak magnetic fields by utilizing the magnetoresistive effect of superconductors due to weak coupling of oxide superconductors.

<Problem to be solved by the invention> The magnetoresistive element using the semiconductor or magnetic material described above has a small change in the resistance of the magnetoresistive element with respect to a change in the magnetic field when the strength of the magnetic field to be measured is small. Methods such as applying a bias magnetic field to improve the sensitivity of the magnetoresistive element or moving it to a range with good linearity have been used, but it has been difficult to accurately measure weak magnetic fields.

Additionally, those that use the magnetoresistive effect of superconductors have a low frequency fluctuation phenomenon of 10 Hz or less in their output voltage, making it difficult to measure weak magnetic fields when using direct current or bias current with a frequency of 10 Hz or less. Met.

It is an object of the present invention to solve the problems of conventional magnetic field measurement methods and to provide a method for efficiently measuring magnetic fields with high accuracy.

<Means for Solving the Problems> The above-mentioned problems regarding magnetic field measurement can be solved by a method that utilizes the magnetoresistive effect of a superconductor at a frequency higher than its characteristic fluctuation frequency. First, a superconducting magnetoresistive element has a structure in which a pair of current electrodes and voltage electrodes are provided near both ends of a superconductor that has weak coupling at grain boundaries. When a magnetic field with a strength greater than the value is applied, the superconductor transitions to normal conductivity,
From the transition point, an electrical resistance value rapidly increases and an output voltage proportional to the electrical resistance value is outputted from the voltage electrode.

A high-frequency AC bias magnetic field that is not affected by the unique fluctuation frequency of the superconducting magnetoresistive element is also applied to the superconducting magnetoresistive element,
By inputting the output of the superconducting magnetoresistive element and the AC bias magnetic field generation signal to a lock-in amplifier, the component due to the AC bias magnetic field is extracted from the output of the element, and the output is compared with the characteristics of the superconducting magnetoresistive element. This is used to measure the strength of the external magnetic field.

In addition, measurement is made convenient by providing means for applying a DC bias magnetic field to bring the above-mentioned superconducting magnetoresistive element into a highly sensitive magnetic field strength range.

Function> By providing two coils, an AC magnetic field generating coil and a DC magnetic field generating coil, in the same direction for a superconducting magnetoresistive element, highly sensitive magnetic field measurements can be performed using the highly sensitive part of the element. It is something.

When the coil generates an alternating magnetic field, the output generated at the voltage electrode of the element is input to the lock-in amplifier along with the magnetic field generation signal, and only the component due to the alternating magnetic field can be measured with high accuracy. Furthermore, by changing the strength of the magnetic field from a coil that applies a DC magnetic field of known strength to the element, and by changing the output of the lock-in amplifier, it is possible to measure weak magnetic fields with high sensitivity.

<Example> Embodiments of the present invention will be described below with reference to the drawings.

The superconducting magnetoresistive element 14 shown in FIG. 2 is a detailed explanation of the element 14 used in this example. In Figure 2, a superconducting film 2 is formed on a non-magnetic substrate l, consisting of a weakly bonded aggregate of minute oxide superconductor particles bonded through an extremely thin insulating film or in a point shape. 2 into a meandering shape by mechanical processing, and then titanium (Ti) is deposited by vapor deposition.
Current electrodes 3 av 3 b and voltage electrodes 4 a * 4 b
are formed to form the superconducting magnetoresistive element 14. FIG. 2 et al.) are front views of the element 14, showing that when this element is used, a constant current power source 5 is connected to the current electrodes 8a, 8b, and an output voltage measuring device is connected to the voltage electrodes. Second
Figure (b) is a cross-sectional view of the element.

FIG. 3 shows an outline of an apparatus for producing the superconducting film 2 shown in FIG. 2 by a spray pyrolysis method.

In the case of a Y-Ba-Cu-0 based superconductor, the raw material Y
(NOs )s ・6 Hz Os Ba (NO
Weigh out s h and Cu (NOs h ・8H 0) into a predetermined composition (YBazCus) and make it into an aqueous solution 7,
Pour compressed air into the container 8 of the spray gun 9 and into the pipe 10.
The substrate 13 was heated to about 600° C. with a heater 12, and was sprayed in small amounts 11 from a spray gun 9, thereby showing a state in which it was turned into a ceramic by thermal decomposition.

The above superelectric film was made to have a thickness of about 10 μm and was heat-treated in air.

The above-mentioned superconducting film may have a different composition, or may use other manufacturing methods with different manufacturing conditions. Also, the film thickness is 1 to 1
Good results were obtained between 0 μm.

As shown in FIG. 1, the superconducting magnetoresistive element 14 configured as shown in FIG. The measurements were conducted in a magnetically shielded room free of magnetic noise.

Connect the cari/l/15 to an AC power supply, and the cari/l/16
is connected to a DC power source so that an AC magnetic field and a DC magnetic field can be applied to the element 14, respectively.

(The illustration of the power source for the coil is omitted.) FIG. 4 shows an example of the output characteristics of the element 14 having the above configuration. This figure shows the output of the superconducting magnetoresistive element 14 measured by applying a direct current magnetic field using a coil A/16 with a bias current of 10 mA flowing through the current a of the superconducting magnetoresistive element 14. The vertical axis represents the output of the element, and the horizontal axis represents the strength of the DC bias current.

The next figure 5 shows the superconducting magnetoresistive element 1 explained in figure 4.
Under measurement conditions 4, when the DC bias magnetic field is changed as shown on the horizontal axis, the magnitude of noise included in the output of the element is shown on the vertical axis for each frequency.

Figure 5 shows that the noise from the element 14 does not change much with the strength of the applied magnetic field, but the noise is large at low frequencies of several Hz or less, and precise magnetic field measurements are difficult due to direct current and low-frequency magnetic fields. It is shown that.

The present invention uses the method described below to accurately measure the characteristics of the superconducting magnetoresistive element 14, without being affected by the noise of the element 14, even in a magnetic field that changes with direct current or low frequency.

FIG. 6 shows an AC waveform of one embodiment of the present invention. This FIG. 6 also has the configuration shown in FIG. 1, and a sine wave of +100 mGauss at IKHz is applied using a carp IV15 (waveform in FIG. 6(a)).

A in FIG. 7 is a graph of the content explained in FIG. 4 when a predetermined current is applied to the carp/l/16 while an alternating current is applied to the carp/l/15 as described above.

When the DC bias magnetic field corresponding to points B, C, D, and E is applied, the corresponding alternating current peak waveforms of the element 14 that generate tingles are shown in Fig. 6 (b), (c), (d) - (e ) and (f)
It shows that it will become.

The above output signal and the alternating current magnetic field generation signal are input to the lock-in amplifier, and the lKH2 precept component is extracted in a narrow band, making it possible to keep the effective value of noise low.

An overview of the above lock-in amplifier is shown in the block diagram of FIG. The output from voltage electrode 4 of element 14 is amplified 20 times by a differential amplifier and input to a lock-in amplifier. On the other hand, as a reference input, I K H of the sine wave generator
A z signal is used.

The principle of a lock-in amplifier is as follows. The input signal V 8 w reference signal Vr is expressed as follows.

Vr = Acos(ωrt+θ) ---(1
)Vs = cos(ωst) ...self (
2) Here, A: constant, ωr: angular velocity of the reference signal.

θ: Phase angle, ωS is the angular velocity of the two-person force signal. Upper 2
Phase 5 sensitive signal
When multiplied by the vector (phase comparator), the next signal V
It becomes psd.

Vpsd=Acos(ωrt+θ)IICOs(ωst
)・・・(3) Here, since ωr and ωS are equal, the second term in equation (3) becomes a DC component. Also, since the alternating current component in the first term of equation (3) is removed by the low-pass filter, the output VLP from the low-pass filter is as follows.

In order to maximize vLP here, the lock-in amplifier should be adjusted so that the phase difference between the reference signal and the input signal becomes zero. As described above, only the frequency component due to the applied AC magnetic field can be extracted as a DC voltage.

Figure 9 shows the measurement results, with the horizontal axis representing the strength of the DC bias magnetic field when changing the value of the DC current flowing through the coil/l/15, and the output of the lock-in amplifier representing the vertical axis.

In Figure 9, the differential magnetic sensitivity at the operating point due to the applied DC magnetic field is measured as the lock-in amplifier output, but when the DC magnetic field is near zero, the output waveform changes from the output characteristics of the superconducting magnetoresistive element as described above. Figure 6 (c) Gi) le)
In this example, a linear region existed as shown in FIG. By using this linear region and setting the time constant of the low-pass filter of the lock-in amplifier to 100 m5ec, it is possible to
The magnetic field of z could be measured with a resolution of 0.1 mGauas.

The above is an explanation of the embodiments, but the present invention is not limited to the embodiments, and the present invention is not limited to the embodiments. The range and accuracy of magnetic field measurement can be changed by applying or not applying a DC bias magnetic field, or by changing its strength.

Also, the bias magnetic field explained with two coils in the example is
A method may be used in which direct current and alternating current are passed through one coil. Furthermore, by changing the time constant of the low-pass filter of the lock-in amplifier, it is also possible to measure magnetic fields that change at several Hz or more.

The structure also consists of a thin film coil for applying a bias magnetic field formed on the same substrate as the superconducting magnetoresistive element, which stabilizes the magnetic measurement.
It is also possible to simplify the production.

<Effects of the Invention> The present invention is a method that makes it possible to measure even weak magnetic fields with high resolution by eliminating the influence of inherent low frequency noise of several Hz or less that superconducting magnetoresistive elements have.

Furthermore, it is possible to miniaturize elements and coils, and it is also possible to measure the spatial distribution of minute magnetic fields, making it possible to use it in various fields such as medicine and non-destructive testing.

[Brief Description of the Drawings] Fig. 1 is a schematic perspective view of an embodiment of the present invention, Fig. 2 is a structural diagram of a superconducting magnetoresistive element of the embodiment, and Fig. 8 is an explanation of a ceramic manufacturing method by spray pyrolysis. Figure 4 is a DC bias magnetic field-output characteristic diagram for the superconducting magnetoresistive element of the example, and Figure 5 is a DC bias magnetic field of the element in Figure 4.
Noise characteristic diagram, Figure 6 is a DC bias magnetic field strength vs. output waveform diagram, Figure 7 is a diagram showing the operating point of Figure 6, Figure 8 is a block diagram of the lock-in amplifier, Figure 9 is the main FIG. 3 is a DC magnetic field-lock-in amplifier output characteristic diagram according to an embodiment of the invention. 1.13...Substrate, 2...Superconducting film, 3.
... Current electrode, 4... Voltage type, 5... Constant current power supply, 6... Voltmeter, 7... Aqueous solution,
8... Container, 9... Spray gun, 10.
...pipe, 11...spraying. 12...Heater 14...Superconducting magnetoresistive element. 15... AC bias magnetic field coil, 16...
DC bias magnetic field coil.

Claims (1)

[Claims] 1. In a magnetic field measuring device using a magnetoresistive element made of a superconductor having weakly coupled grain boundaries, means for applying an alternating current bias magnetic field to the magnetoresistive element is provided, A superconducting magnetic field measurement device characterized in that an external magnetic field is measured using an output signal generated by applying the alternating current bias magnetic field. 2. The superconducting magnetic field measuring device according to claim 1, further comprising means for applying a DC bias magnetic field in the direction of the AC bias magnetic field applied to the magnetoresistive element.