阅读说明：本技术 一种交流磁化率测量装置及方法 (alternating current magnetic susceptibility measuring device and method ) 是由 冯长沙 黄社松 王凡 杨威 于 2019-10-10 设计创作，主要内容包括：本发明公开一种交流磁化率测试装置及方法,包括：交流电流源、温控仪、真空泵、低温恒温器及线圈组；装置还包括：前置放大器、锁相放大器和程控计算机；本申请采用电流激励,将待测试固体或粉末材料放置在拾取线圈,然后一并安置到低温恒温器样品腔内；通过恒流源对激励线圈提供交流电信号,同时锁相放大器提取拾取线圈的测试信号,待测试样品温度通过高精度温控仪获得,然后计算机实时显示测量信号随温度变化的曲线。本申请是一种无损交流磁化率测量方法,解决了传统交流磁化率测试过程中产生的问题,传统方法因为采用恒压激励模式,由于温度变化引起激励线圈阻抗变化,进一步引起被测材料磁化率信号测量分辨率下降,甚至测不出结果的问题。(the invention discloses an alternating current magnetic susceptibility testing device and a method, comprising the following steps: the device comprises an alternating current source, a temperature controller, a vacuum pump, a cryostat and a coil group; the device still includes: the device comprises a preamplifier, a phase-locked amplifier and a program control computer; the method comprises the steps of adopting current excitation, placing a solid or powder material to be tested on a pickup coil, and then placing the pickup coil and the solid or powder material into a sample cavity of a cryostat; an alternating current signal is provided for the exciting coil through a constant current source, meanwhile, a phase-locked amplifier extracts a test signal of a pickup coil, the temperature of a sample to be tested is obtained through a high-precision temperature controller, and then a computer displays a curve of the test signal changing along with the temperature in real time. The application relates to a nondestructive alternating current magnetic susceptibility measuring method, which solves the problems generated in the traditional alternating current magnetic susceptibility testing process, and the traditional method adopts a constant voltage excitation mode, so that the problem that the measurement resolution of a measured material magnetic susceptibility signal is reduced and even the result cannot be measured due to the impedance change of an excitation coil caused by the temperature change.)

1. an alternating current magnetic susceptibility testing device comprising: the device comprises an alternating current source, a temperature controller, a vacuum pump, a cryostat and a coil group; the method is characterized in that:

The vacuum pump is connected with the cryostat, the cryostat is connected with the temperature controller, and the alternating current source is connected with the coil assembly;

The alternating current source is used for providing an alternating current signal for the coil assembly;

the temperature controller is used for monitoring and controlling the temperature of the sample to be detected and the coil group;

The vacuum pump is used for pumping air in the cryostat and keeping a vacuum cavity of the cryostat in a vacuum state;

the cryostat is used for providing temperature environments required by the sample to be tested and the coil group;

the coil assembly receives an alternating current excitation signal provided by an alternating current source and measures a magnetic susceptibility signal.

2. the ac magnetic susceptibility measurement device according to claim 1, wherein:

and the vacuum pump is connected with the vacuum cavity of the cryostat, and is used for vacuumizing by using the vacuum pump and keeping the vacuum cavity of the cryostat in a vacuum state.

3. The alternating-current magnetic susceptibility measurement device according to claim 1 or claim 2, characterized in that:

the cryostat is provided with a sample cavity, a sample support for bearing a tested sample and a coil group is arranged in the cryostat, the temperature sensor is arranged on the surface of the sample support, the heater is arranged in the sample support of the cryostat, and the temperature sensor and the heater are respectively connected with the temperature controller.

4. the ac magnetic susceptibility measurement device according to claim 1, wherein:

the temperature controller reads the temperature data of the sample support in real time and controls the heater to control the temperature of the sample support in real time through the temperature controller.

5. the ac magnetic susceptibility measurement device according to claim 1, wherein:

The coil group comprises an exciting coil, a pickup coil and a compensating coil, wherein the exciting coil is arranged at the outermost layer, the pickup coil and the compensating coil are arranged in the exciting coil side by side, the pickup coil and the compensating coil are oppositely arranged according to the winding direction, and a sample to be tested is arranged at the center of the pickup coil.

6. the ac magnetic susceptibility measurement device according to claim 1, wherein:

the ac magnetic susceptibility measuring apparatus further includes: the coil group is connected with the preamplifier, and the preamplifier is connected with the phase-locked amplifier;

The preamplifier is used for picking up a magnetic susceptibility signal measured by the coil group, and transmitting the amplified magnetic susceptibility signal to the phase-locked amplifier after amplification;

And the phase-locked amplifier is used for measuring the alternating current magnetic susceptibility signal amplified by the preamplifier and sending the alternating current magnetic susceptibility signal amplified by the phase lock to the program control computer.

7. The ac magnetic susceptibility measurement device according to claim 1, wherein:

the alternating current magnetic susceptibility measuring device also comprises a program control computer which is respectively connected with the alternating current source and the phase-locked amplifier;

The program control computer runs Labview testing software, receives and stores the measurement data transmitted by the lock-in amplifier and the temperature controller, automatically reads the measurement data in real time and displays the curve of the alternating current magnetic susceptibility signal changing along with the temperature in real time.

8. The ac magnetic susceptibility measuring device according to claim 5, wherein the excitation source of the excitation coil is a programmable constant current source; the exciting coil is connected to the output end of the alternating current source and provides an alternating current exciting signal; the pick-up coil and the compensation coil are connected in series and connected to the input end of the preamplifier, the output end of the preamplifier is connected to the input end of the phase-locked amplifier, and the magnetic susceptibility signal is measured.

9. the ac magnetic susceptibility measurement device according to claim 3, wherein:

and the sample holder bonding part are coated with low-temperature vacuum heat-conducting grease.

10. the ac magnetic susceptibility measurement device according to claim 1, wherein:

and the coil groups are wound by enameled pure copper wires.

11. The alternating-current magnetic susceptibility measurement device according to claim 1 or claim 6, characterized in that:

The alternating current source and the coil group, the preamplifier and the coil group, and the phase-locked amplifier and the preamplifier are all connected by coaxial lines.

12. an alternating current magnetic susceptibility measuring method comprises the following specific steps:

Step 1: inspecting the coil assembly: before measurement, the coil group is ensured not to be broken or the enameled insulation layer is damaged, and if the coil group is broken or the enameled insulation layer is damaged, a new coil needs to be replaced;

step 2: placing a sample to be tested: ensuring that a sample to be tested is contacted with a sample holder of the cryostat;

and step 3: vacuumizing the vacuum cavity of the cryostat by using a vacuum pump, and keeping the vacuum pump running all the time during measurement;

and 4, step 4: starting the cryostat to start cooling;

and 5: opening the temperature controller, reading the temperature data of the sample holder in real time by the temperature controller, and controlling the temperature of the sample holder in real time by controlling the heater by the temperature controller;

Step 6: opening an alternating current source, setting alternating current frequency and alternating current magnitude, supplying power to an exciting coil in a coil set through the alternating current source, measuring a magnetic susceptibility signal by the coil set, picking up the magnetic susceptibility signal measured by the coil set by a preamplifier, measuring the alternating current magnetic susceptibility signal amplified by the preamplifier by a phase-locked amplifier, and sending the alternating current magnetic susceptibility signal amplified by the phase-locked amplifier to a program control computer;

and 7: and opening the program control computer, operating Labview testing software, receiving and storing the measurement data transmitted by the lock-in amplifier and the temperature controller, automatically reading the measurement data in real time, and displaying the curve of the alternating current magnetic susceptibility signal changing along with the temperature in real time.

Technical Field

The invention relates to the technical fields of superconducting electronics, material science, high-voltage science and technology and condensed state physics, in particular to an alternating current magnetic susceptibility measuring device and method.

background

The measurement of the alternating magnetic susceptibility was of great importance for the study of magnetic materials since the last 30 centuries, especially materials with ferromagnetic, antiferromagnetic and superconducting transitions, and this method was increasingly valued because many materials have a frequency-dependent magnetic susceptibility and further information on the time constant associated with magnetomotive force is available. For example, the pinning energy and the magnetic relaxation time constant in the superconducting material can be studied by adopting the alternating-current magnetic susceptibility, and the relaxation process for controlling the energy exchange between spin-lattice vibration, the spin-spin relaxation process for the energy exchange between spins of the same kind, the cross relaxation process for the energy exchange between different spins, and the like can be determined; as another example, when a spin glass material is measured, its AC susceptibility peaks at freezing temperatures and drifts as the AC field frequency changes.

the common alternating current magnetic susceptibility measurement adopts a mutual inductance method, namely a pair of coils wound on the same hollow shaft is divided into an exciting coil and a pickup coil, an alternating voltage signal is provided for the exciting coil, an alternating magnetic field is correspondingly generated, the pickup coil generates a signal due to induced current under the action of the alternating magnetic field of the exciting coil, when a measured sample is placed in the center of the pickup coil, a sudden change signal, namely a phase change signal of a material, can appear when the signal in the pickup coil changes the phase of the measured material along with the temperature change, and the attention of researchers is paid.

because the existing alternating current magnetic susceptibility measurement technology is generally driven by a voltage source or a power amplifier, the problem of room temperature or constant temperature alternating current magnetic susceptibility measurement is not solved, but when substances such as superconducting materials, magnetic materials and the like are measured, the change of the alternating current magnetic susceptibility characteristic of the materials along with the temperature is generally concerned, so that the phase change transition temperature of the materials is found. During the temperature change, the temperature of the exciting coil also changes with time. Since the coil is wound from pure copper wire, the resistivity of copper will vary significantly with temperature, and therefore the impedance of the excitation coil will vary significantly with temperature. If constant voltage excitation is used, the current in the excitation coil will also vary significantly with temperature. The current in the excitation coil determines the magnitude of the magnetic field generated by the excitation coil according to maxwell's equations. If the current in the excitation coil varies significantly with temperature, the excitation magnetic field strength also varies with temperature, which causes the output voltage signal of the pick-up coil to fluctuate with temperature. If the size of the measured material is small or the amplitude of the change of the alternating-current magnetic susceptibility along with the temperature is not obvious, the output voltage signal is covered by background noise caused by temperature fluctuation, so that the resolution of an alternating-current magnetic susceptibility system is reduced.

Aiming at the problem that the alternating current magnetic susceptibility signal of the material to be measured is weak, the number of turns of the test coil is increased and the excitation signal is increased in the conventional method, but with the increase of the number of turns of the coil and the increase of the excitation signal, the background noise is correspondingly increased, and the corresponding problem is not improved when the alternating current magnetic susceptibility is measured under a cryostat.

disclosure of Invention

in order to solve the defects in the prior art, the application provides an alternating current magnetic susceptibility measuring device and method, and mainly solves the problems that in the traditional alternating current magnetic susceptibility testing process, the impedance of an exciting coil changes due to temperature changes when a constant voltage exciting mode is adopted, and the measured resolution of a measured material magnetic susceptibility signal is further reduced or cannot be measured. An excitation source of an excitation coil is changed into a programmable constant current source, which is different from the common constant voltage excitation adopted in the existing susceptibility test;

an alternating current magnetic susceptibility measuring apparatus: the method comprises the following steps: the device comprises an alternating current source, a temperature controller, a vacuum pump, a cryostat and a coil group;

The vacuum pump is connected with the cryostat, the cryostat is connected with the temperature controller, and the alternating current source is connected with the coil assembly;

the alternating current source is used for providing an alternating current signal for the coil assembly;

the temperature controller is used for monitoring and controlling the temperature of the sample to be detected and the coil group;

the vacuum pump is used for pumping air in the cryostat and keeping a vacuum cavity of the cryostat in a vacuum state;

the cryostat is used for providing temperature environments required by the sample to be tested and the coil group;

the coil assembly receives an alternating current excitation signal provided by an alternating current source and measures a magnetic susceptibility signal.

and the vacuum pump is connected with the vacuum cavity of the cryostat, and is used for vacuumizing by using the vacuum pump and keeping the vacuum cavity of the cryostat in a vacuum state.

The cryostat is provided with a sample cavity, a sample support for bearing a tested sample and a coil group is arranged in the cryostat, the temperature sensor is arranged on the surface of the sample support, the heater is arranged in the sample support of the cryostat, and the temperature sensor and the heater are respectively connected with the temperature controller.

The temperature controller reads the temperature data of the sample support in real time and controls the heater to control the temperature of the sample support in real time through the temperature controller.

the coil group comprises an exciting coil, a pickup coil and a compensating coil, wherein the exciting coil is arranged at the outermost layer, the pickup coil and the compensating coil are arranged in the exciting coil side by side, the pickup coil and the compensating coil are oppositely arranged according to the winding direction so as to offset background noise, and a sample to be tested is arranged at the center of the pickup coil.

The ac magnetic susceptibility measuring apparatus further includes: the coil group is connected with the preamplifier, and the preamplifier is connected with the phase-locked amplifier;

the preamplifier is used for picking up a magnetic susceptibility signal measured by the coil group, and transmitting the amplified magnetic susceptibility signal to the phase-locked amplifier after amplification;

and the phase-locked amplifier is used for measuring the alternating current magnetic susceptibility signal amplified by the preamplifier and sending the alternating current magnetic susceptibility signal amplified by the phase lock to the program control computer.

the alternating current magnetic susceptibility measuring device also comprises a program control computer which is respectively connected with the alternating current source and the phase-locked amplifier;

the program control computer runs Labview testing software, receives and stores the measurement data transmitted by the lock-in amplifier and the temperature controller, automatically reads the measurement data in real time and displays the curve of the alternating current magnetic susceptibility signal changing along with the temperature in real time.

The excitation source of the excitation coil is a programmable constant current source;

Excitation coils in the coil sets are connected to the output end of an alternating current source to provide alternating current excitation signals; the pick-up coil and the compensation coil are connected in series and then connected to the input end of a preamplifier, the output end of the preamplifier is connected to the input end of a phase-locked amplifier, and a magnetic susceptibility signal is measured;

The temperature controller, the phase-locked amplifier and the alternating current source are all connected to the program control computer to automatically test the curve of the alternating current magnetic susceptibility changing along with the temperature.

and the sample holder bonding part are coated with low-temperature vacuum heat-conducting grease.

the coil groups are wound by using enameled pure copper wires;

The alternating current source and the coil group, the preamplifier and the coil group, and the phase-locked amplifier and the preamplifier are all connected by coaxial lines.

an alternating current magnetic susceptibility measuring method is realized by adopting an alternating current magnetic susceptibility measuring device, and comprises the following specific steps:

Step 1: inspecting the coil assembly: before measurement, the coil group is ensured not to be broken or the enameled insulation layer is damaged, the phenomena of coil disconnection and short circuit are avoided, and if the coil group is broken or the enameled insulation layer is damaged, a new coil needs to be replaced;

Step 2: placing a sample to be tested: ensuring that the sample to be tested is well contacted with the sample holder of the cryostat so as to ensure that the cold energy of the cryostat can be quickly transferred to the material to be tested in the measurement;

and step 3: vacuumizing a vacuum cavity of the cryostat by using a vacuum pump; and keeping the vacuum pump running at all times during the measurement;

And 4, step 4: starting the cryostat to start cooling;

And 5: opening the temperature controller, reading the temperature data of the sample holder in real time by the temperature controller, and controlling the temperature of the sample holder in real time by controlling the heater by the temperature controller;

Step 6: opening an alternating current source, setting alternating current frequency and alternating current magnitude, supplying power to an exciting coil in a coil set through the alternating current source, measuring a magnetic susceptibility signal by the coil set, picking up the magnetic susceptibility signal measured by the coil set by a preamplifier, measuring the alternating current magnetic susceptibility signal amplified by the preamplifier by a phase-locked amplifier, and sending the alternating current magnetic susceptibility signal amplified by the phase-locked amplifier to a program control computer;

And 7: and opening the program control computer, operating Labview testing software, receiving and storing the measurement data transmitted by the lock-in amplifier and the temperature controller, automatically reading the measurement data in real time, and displaying the curve of the alternating current magnetic susceptibility signal changing along with the temperature in real time.

The vacuum pump is preferably a molecular pump set;

the beneficial technical effects are as follows:

1. the application changes the excitation source of the excitation coil into a programmable constant current source. In the process of system temperature change, although the impedance of the exciting coil changes along with the temperature, the current in the coil is not changed, so the exciting magnetic field intensity is constant and does not change along with the temperature. This greatly reduces the temperature-dependent fluctuation of the background of susceptibility measurements, thereby improving the resolution of the overall system.

2. The strength of the excitation magnetic field can be conveniently changed by adopting the programmable constant current source, when a small sample needs to be measured, the excitation current can be increased, and the excitation magnetic field is improved, so that the amplitude of the output voltage of the pickup coil is increased, the system noise can be inhibited, and the resolution of the system is improved;

3. when this application utilizes in under the ultra-low temperature environment, can be through reducing exciting current to reduce the coil and generate heat, do not increase the minimum temperature of system, this ability that has just increased the compatible cryogenic facilities of measurement system.

4. the magnetic field intensity generated by the exciting coil is in direct proportion to the exciting current, so that the value of the exciting magnetic field can be accurately calculated, and the accuracy of the absolute value of the alternating-current magnetic susceptibility of the sample can be improved.

5. The computer is adopted to integrate the test instruments together, the measurement data can be automatically read and stored in real time, the measurement data cannot be lost when accidents such as power failure occur, the curve of the alternating current magnetic susceptibility signal changing along with the temperature is displayed in real time, the measurement condition can be conveniently and timely mastered, and the method is an accurate, efficient and reliable measurement means.

drawings

FIG. 1 is a schematic diagram of the overall structure of an AC magnetic susceptibility measuring device according to the present invention;

FIG. 2 is a partial enlarged view of a coil assembly of an AC magnetic susceptibility measuring device according to the present invention;

FIG. 3 is a flow chart of an AC magnetic susceptibility measurement method of the present invention;

FIG. 4 is a graph of magnetic susceptibility data measured by an AC magnetic susceptibility measuring device according to the present invention;

in the figure:

1-program control computer, 2-phase-locked amplifier, 3-alternating current source, 4-temperature controller, 5-preamplifier, 6-vacuum pump, 7-cryostat, 8-coil group, 801-exciting coil, 802-pickup coil, 803-compensating coil.

Detailed Description

the present application is further described below with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present application is not limited thereby.

the application is an alternating current magnetic susceptibility measuring device, the whole structure of which is shown in the following figure 1, and the device comprises an alternating current source 3, a temperature controller 4, a vacuum pump 6, a cryostat 7 and a coil group 8;

the vacuum pump 6 is connected with the cryostat 7, the cryostat 7 is connected with the temperature controller 4, and the alternating current power supply 3 is connected with the coil group 8;

The alternating current source 3 is used for providing alternating current signals for the coil assembly 8;

the temperature controller 4 is used for monitoring and controlling the temperature of the sample to be detected and the coil group 8;

the vacuum pump 6 is used for pumping air in the cryostat 7 and keeping a vacuum cavity of the cryostat 7 in a vacuum state;

the cryostat 7 is used for providing a temperature environment required by the sample to be tested and the coil group 8 and keeping the constant temperature state of the sample to be tested and the coil group 8;

the coil group 8 receives an alternating current excitation signal provided by the alternating current source 3 and measures a magnetic susceptibility signal;

And the vacuum pump 6 is connected with the vacuum cavity of the cryostat 7, and is used for vacuumizing by using the vacuum pump 6 and keeping the vacuum cavity of the cryostat 7 in a vacuum state.

The cryostat 7 is provided with a sample cavity, a sample support for bearing a tested sample and the coil group 8 is arranged in the cryostat, the temperature sensor is arranged on the surface of the sample support, the heater is arranged in the sample support of the cryostat 7, and the temperature sensor and the heater are respectively connected with the temperature controller 4.

the temperature controller 4 reads the temperature data of the sample support in real time, and controls the heater to control the temperature of the sample support in real time through the temperature controller 4.

the coil assembly 8 comprises an excitation coil 801, a pickup coil 802 and a compensation coil 803, the excitation coil 801 is at the outermost layer, the pickup coil 802 and the compensation coil 803 are arranged in the excitation coil 801 side by side, the pickup coil 802 and the compensation coil 803 are arranged oppositely according to the winding direction, and a sample to be tested is arranged at the center of the pickup coil 802, as shown in fig. 2.

The ac magnetic susceptibility measuring apparatus further includes: the coil assembly 8 is connected with the preamplifier 5, and the preamplifier 5 is connected with the lock-in amplifier 2;

the preamplifier 5 is used for picking up a magnetic susceptibility signal measured by the coil group, amplifying the magnetic susceptibility signal and transmitting the amplified magnetic susceptibility signal to the phase-locked amplifier;

the phase-locked amplifier 2 is used for measuring the alternating current magnetic susceptibility signal amplified by the preamplifier 5 and sending the alternating current magnetic susceptibility signal amplified by the phase lock to the program control computer 1;

The alternating current magnetic susceptibility measuring device also comprises a program control computer 1, and the program control computer 1 is respectively connected with an alternating current source 3 and a phase-locked amplifier 2;

the program control computer 1 runs Labview testing software, receives and stores the measurement data transmitted by the lock-in amplifier 2 and the temperature controller 4, automatically reads the measurement data in real time, and displays the curve of the alternating current susceptibility signal changing along with the temperature in real time;

the excitation source of the excitation coil 801 is a programmable constant current source; the exciting coil 801 is connected to the output end of the alternating current source 3 to provide an alternating current exciting signal; the pick-up coil 802 and the compensation coil 803 are connected in series and then connected to the input end of the preamplifier 5, the output end of the preamplifier 5 is connected to the input end of the phase-locked amplifier 2, and a magnetic susceptibility signal is measured;

And the sample holder bonding part are coated with low-temperature vacuum heat-conducting grease.

The coil groups 8 are all wound by enameled pure copper wires.

The alternating current source 3 and the coil group 8, the preamplifier 5 and the coil group 8, and the lock-in amplifier 2 and the preamplifier 5 are all connected by coaxial lines.

embodiments of the present application will be described in detail below with reference to the accompanying drawings:

The cryostat 7 is provided with a closed vacuum cavity structure, a vacuum pump 6 is required to be connected to the vacuum cavity through a pipeline for pumping vacuum of the vacuum cavity, and a vacuum valve can be added on the pipeline to facilitate the control of the on-off of the vacuum pipeline;

a sample support for bearing a sample to be tested is arranged in the cryostat 7, cold energy is transferred to a solid or powder material to be tested, in order to increase thermal contact, a thin layer of Apiezon N grease is coated on the contact surface, and the function of fixing the sample to be tested can be achieved; the temperature near the sample holder is collected to the program control computer 1 in real time through a temperature controller 4 connected to a high temperature sensor and stored;

the lead wire led out from the exciting coil 801 is connected to an alternating current source 3, the lead wire led out from the pickup coil 802 is connected to a preamplifier 5, and the signal is amplified and then is accessed to a phase-locked amplifier 2 for reading;

the input signal and the read signal are connected to the corresponding instruments through coaxial lines, so that external electromagnetic interference can be well shielded, and all the test instruments are connected to the program control computer 1 through remote communication ports;

in the device, a control program is compiled by a program control computer 1 by adopting Labview software, so that each test instrument can be conveniently and quickly subjected to communication control, and the device has the functions of acquiring and storing data in real time and displaying a change curve of the magnetic susceptibility along with the temperature in real time during measurement;

Based on the above measurement method, as shown in fig. 3 below, the test is mainly completed by the following 7 steps:

step 1: the inspection coil set 8;

before testing, checking whether the coil group 8 is broken or the enameled insulation layer is damaged, avoiding the phenomena of disconnection and short circuit of any coil in the coil group 8, and if the coil group is broken or the enameled insulation layer is damaged, replacing a new coil;

Step 2: placing a sample to be tested:

the material to be measured is placed in the center of a pickup coil 802 of a coil group 8, and low-temperature heat conduction grease is smeared between the material to be measured and a sample holder of a cryostat 7, so that good thermal contact is ensured, and the cold energy of the cryostat can be quickly transferred to the material to be measured in measurement;

and step 3: vacuumizing a vacuum cavity of the cryostat 7;

a vacuum pump 6 is adopted to carry out vacuum extraction on a vacuum cavity of a cryostat 7, and the vacuum pump is kept running all the time during measurement;

and 4, step 4: starting the cryostat 7 to start cooling;

And 5: monitoring and controlling the temperature near the sample in the cryostat 7 in real time;

Opening the temperature controller 4, checking whether the temperature display is normal, then monitoring and acquiring temperature data near the sample holder in the cryostat 7 in real time, and controlling the temperature change rate according to the requirement;

step 6: measuring the signal of the pick-up coil 802;

The alternating current source 3 is turned on, alternating current with certain frequency and certain amplitude is provided for the exciting coil 801, an output signal is amplified by the preamplifier 5 and then enters the phase-locked amplifier 2 to read a signal, the phase-locked amplifier measures an alternating current magnetic susceptibility signal amplified by the preamplifier, and the alternating current magnetic susceptibility signal amplified by the phase-locked amplifier is sent to the program control computer;

and 7: the measured data are recorded and an ac susceptibility curve is given in real time.

opening the program control computer 1, operating Labview testing software, reading temperature data near a sample holder in the cryostat 7 through a temperature controller, receiving an alternating current magnetic susceptibility signal of the pickup coil 802 measured by the phase-locked amplifier 2 in real time, automatically reading the measured data in real time, and displaying a curve of the alternating current magnetic susceptibility signal changing along with the temperature in real time;

as shown in fig. 4, the lock-in amplifier 2 detects that the ac magnetic susceptibility signal of the pickup coil 802 includes a real part Y and an imaginary part X (Y + iX), where the real part Y reflects the shielding amount of the material to the ac magnetic field, and when the material starts to generate a magnetic phase transition (near the critical temperature), the real part Y rapidly decreases; the imaginary part X reflects the dissipation of the magnetic field energy during the superconducting phase transition, which tends to be 0.

The present applicant has described and illustrated embodiments of the present invention in detail with reference to the accompanying drawings, but it should be understood by those skilled in the art that the above embodiments are merely preferred embodiments of the present invention, and the detailed description is only for the purpose of helping the reader to better understand the spirit of the present invention, and not for limiting the scope of the present invention, and on the contrary, any improvement or modification made based on the spirit of the present invention should fall within the scope of the present invention.