CN109655771B - AC magnetic susceptibility measuring device and measuring method thereof - Google Patents
AC magnetic susceptibility measuring device and measuring method thereof Download PDFInfo
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- CN109655771B CN109655771B CN201710941542.2A CN201710941542A CN109655771B CN 109655771 B CN109655771 B CN 109655771B CN 201710941542 A CN201710941542 A CN 201710941542A CN 109655771 B CN109655771 B CN 109655771B
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Abstract
The invention provides an alternating current magnetic susceptibility measuring device, comprising: an excitation coil for generating an excitation magnetic field in an energized state; the Hall sensor is positioned in the exciting coil and comprises two current input ends and two voltage output ends, and the direction of bias current in the two current input ends is parallel to the direction of an exciting magnetic field in the exciting coil; a first signal generator for providing an alternating current excitation of a first frequency to the excitation coil; the output end of the second signal generator is connected to the two current input ends of the Hall sensor and is used for providing alternating current excitation of a second frequency for the Hall sensor; the phase-locked amplifier measures a voltage output signal of the Hall sensor; and a third signal generator provides a third frequency reference signal for the lock-in amplifier. The alternating-current magnetic susceptibility measuring device has the excellent performances of high measuring precision, high signal-to-noise ratio and the like under low frequency.
Description
Technical Field
The invention relates to the field of magnetic susceptibility measurement, in particular to an alternating current magnetic susceptibility measurement device and a measurement method thereof.
Background
When an alternating magnetic field is applied to a magnetic sample, the magnetic sample can induce to generate an alternating magnetic moment, and the ratio of the magnetic moment to the alternating magnetic field is the alternating magnetic susceptibility of the magnetic sample. Since the magnetic moment of the magnetic sample induced by the alternating magnetic field oscillates with time, the magnetization dynamics information of the sample can be obtained from the alternating magnetic susceptibility. The alternating magnetic susceptibility is an important parameter for characterizing the properties of substances, and has wide application in the fields of spin glass, super-paramagnetic property, magnetic phase transition, superconduction and the like.
Fig. 1 is a schematic diagram of an ac magnetic susceptibility measurement apparatus in the prior art, and as shown in fig. 1, the ac magnetic susceptibility measurement apparatus 1 includes a primary excitation coil 11 and secondary induction coils 12 and 13. The secondary induction coils 12 and 13 are located in the primary excitation coil 11, and have the same number of turns and opposite winding directions. Both ends of the primary excitation coil 11 are connected to an alternating current power supply 14, and the secondary induction coils 12, 13 are connected in series to a voltmeter 15. From [ Mn12O12(CH3COO)16(H2O)4]A magnetic sample 16 (black block shown in fig. 1) to be measured (0.2 mm × 0.4 mm) is placed inside the secondary induction coil 12, the alternating magnetic field generated in the primary excitation coil 11 induces the sample 16 to generate an alternating magnetic moment, the alternating magnetic moment induces an induced electromotive force in the secondary induction coil 12, and the induced electromotive force induced in the secondary coil 12 by the magnetic field generated in the primary coil 11 is cancelled by a counter-induced electromotive force generated in the counter-wound secondary coil 13. Therefore, the total induced electromotive force at both ends is generated only by the sample 16 after the secondary coils 12, 13 are connected in series, and the ac magnetic susceptibility information of the magnetic sample 16 is obtained by measuring the induced electromotive force.
Fig. 2 and 3 are graphs showing real and imaginary parts of ac magnetic susceptibility of the magnetic sample measured at 13hz by the ac magnetic susceptibility measuring apparatus shown in fig. 1, respectively, as a function of temperature. As can be seen from fig. 2 and 3, the real part and the imaginary part of the alternating magnetic susceptibility change irregularly with temperature, so that the change rule of the alternating magnetic susceptibility of the magnetic sample with the external environment cannot be known.
Since the above-described principle of measuring the alternating magnetic susceptibility of a magnetic sample using a detection coil is based on the faraday's law of electromagnetic induction, the induced electromotive force is proportional to the rate of change of the magnetic flux in the coil. In the high-frequency measurement area, the induced electromotive forces generated in the secondary induction coils 12 and 13 by the high-frequency magnetic field generated by the primary exciting coil 11 cannot be completely counteracted due to the incomplete symmetry of the secondary coils 12 and 13 in the actual winding process, so that a large measurement background signal is generated. More importantly, the low frequency alternating current in the low frequency measurement zone causes the electromotive force induced on the detection coils 12 and 13 to be low, and thus the signal-to-noise ratio is poor. In addition, the newly discovered magnetic material sample is generally small in volume and small in magnetic moment, which puts higher demands on the measurement accuracy. Therefore, the current ac susceptibility measuring device 1 using a detection coil based on the faraday's law of electromagnetic induction cannot meet the requirement of measuring the ac susceptibility of a sample with a small magnetic moment in a low frequency region.
Disclosure of Invention
In view of the above technical problems in the prior art, an embodiment of the present invention provides an ac magnetic susceptibility measurement apparatus, including:
an excitation coil for generating an excitation magnetic field in an energized state;
the Hall sensor is positioned in the exciting coil and comprises two current input ends and two voltage output ends, and the direction of bias current in the two current input ends is parallel to the direction of an exciting magnetic field in the exciting coil;
the output end of the first signal generator is connected to two ends of the exciting coil and is used for providing alternating current excitation of a first frequency for the exciting coil;
the output end of the second signal generator is connected to the two current input ends of the Hall sensor and is used for providing alternating current excitation of a second frequency for the Hall sensor;
the signal input end of the phase-locked amplifier is connected to the two voltage output ends of the Hall sensor; and
a third signal generator that outputs an ac stimulus at a third frequency to a reference signal input of the lock-in amplifier.
Preferably, the hall sensor is cross-shaped, and two current input ends of the hall sensor are oppositely arranged and parallel to the direction of the excitation magnetic field.
Preferably, the two voltage outputs of the hall sensor are arranged on the same straight line perpendicular to the bias current in the two current inputs.
Preferably, the cross-shaped intersection of the hall sensor has an adhesive for fixing the magnetic sample.
Preferably, the excitation coil is solenoid-shaped.
Preferably, the magnetic field sensor further comprises a bracket made of a non-magnetic material, the bracket is positioned inside the exciting coil, the bracket is provided with a positioning plane parallel to the direction of the exciting magnetic field, and the hall sensor is arranged on the positioning plane.
Preferably, the third frequency is equal to the difference or the sum of the first frequency and the second frequency.
Preferably, the frequencies output by the first signal generator, the second signal generator and the third signal generator are continuously adjustable and have a common clock trigger.
The invention also provides a measuring method based on the alternating-current magnetic susceptibility measuring device, which comprises the following steps:
step 1), adhering a sample to be detected to an induction area of the Hall sensor;
step 2), placing the Hall sensor inside the exciting coil to enable the direction of the bias current of the Hall sensor to be parallel to the direction of an exciting magnetic field inside the exciting coil;
step 3), controlling the temperature of the sample to be detected to be a preset temperature value;
step 4), adjusting the output frequency of the first signal generator to provide alternating current excitation of a first frequency for the exciting coil, adjusting the output frequency of the second signal generator to provide alternating current excitation of a second frequency for the Hall sensor, and adjusting the output frequency of the third signal generator to provide alternating current excitation of a third frequency for the reference signal input end of the phase-locked amplifier;
and 5) measuring the voltage of the voltage output end of the Hall sensor by using the lock-in amplifier.
The alternating-current magnetic susceptibility measuring device has the excellent performances of high measuring precision, excellent signal-to-noise ratio performance and the like under low frequency.
Drawings
Embodiments of the invention are further described below with reference to the accompanying drawings, in which:
fig. 1 is a schematic diagram of an ac magnetic susceptibility measurement device in the prior art.
FIG. 2 is a graph showing [ Mn ] measured by the AC magnetic susceptibility measuring apparatus shown in FIG. 112O12(CH3COO)16(H2O)4](0.2 mm × 0.4 mm) real part of alternating magnetic susceptibility at a magnetic sample frequency of 13hz as a function of temperature.
FIG. 3 is a graph showing [ Mn ] measured by the AC magnetic susceptibility measuring apparatus shown in FIG. 112O12(CH3COO)16(H2O)4](0.2 mm x 0.4 mm) plot of the imaginary part of the alternating magnetic susceptibility at a magnetic sample frequency of 13hz as a function of temperature.
Fig. 4 is a schematic diagram of an ac magnetic susceptibility measurement device according to a preferred embodiment of the invention.
FIG. 5 is a graph showing the measurement of [ Mn ] using the AC magnetic susceptibility measuring apparatus shown in FIG. 412O12(CH3COO)16(H2O)4](0.2 mm. times.0.2 mm. times.0.4 mm) the real part of alternating magnetic susceptibility at frequencies of 3Hz, 13Hz, 33Hz, 77Hz, and 133Hz, respectively, as a function of temperature.
FIG. 6 is a graph showing [ Mn ] measured by the AC magnetic susceptibility measuring apparatus shown in FIG. 412O12(CH3COO)16(H2O)4](0.2 mm. times.0.2 mm. times.0.4 mm) the imaginary part of the alternating magnetic susceptibility at 3Hz, 13Hz, 33Hz, 77Hz and 133Hz, respectively, is plotted as a function of temperature.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail by embodiments with reference to the accompanying drawings.
Fig. 4 is a schematic diagram of an ac magnetic susceptibility measurement device according to a preferred embodiment of the invention. As shown in fig. 4, the ac magnetic susceptibility measuring apparatus 2 includes a support 25, a solenoid-shaped excitation coil 21. The holder 25 is made of a nonmagnetic material, has a semi-cylindrical shape, and has a circular arc surface 251 (shown by a dotted line in fig. 4) that fits a part of the inner side wall of the excitation coil 21 and a positioning plane 252 that is parallel to the axial direction of the excitation coil 21. The ac susceptibility measuring device 2 further comprises a sheet-like hall sensor 22 made of GaAs/AlGaAs heterojunction, the hall sensor 22 being adhered to the positioning plane 252 of the support 25 and being parallel to the positioning plane 252. The hall sensor 22 has a cross shape with oppositely disposed current input terminals 221, 222 and oppositely disposed voltage output terminals 223, 224. Since the current input terminals 221, 222 arranged on the same straight line are parallel to the axial direction of the exciting coil 21, when the current input terminals 221, 222 of the hall sensor 22 are energized, the bias current direction in the hall sensor 22 is parallel to the magnetic field direction inside the exciting coil 21, so that the exciting magnetic field does not induce a hall voltage on the hall sensor 22.
The ac susceptibility measuring device 2 further comprises a lock-in amplifier 23 connected to the voltage outputs 223, 224 of the hall sensor 22, signal generators 2a, 2b and 2c with continuously adjustable frequency, a trigger clock 2d and a computer 26 for data acquisition.
The output of the signal generator 2a is connected to both ends of the excitation coil 21, the output of the signal generator 2b is connected to the current inputs 221, 222 of the hall sensor 22, and the output of the signal generator 2c is connected to the reference signal input 231 of the lock-in amplifier 23, wherein the signal generator 2c and the lock-in amplifier 23 form a voltage measuring device. The trigger clock 2d output is connected to the clock inputs of the signal generators 2a, 2b and 2c so that all three have the same clock trigger.
The measurement principle of the ac magnetic susceptibility measurement device 2 of the present embodiment is as follows:
the signal generator 2a outputs an AC excitation of frequency f to the excitation coil 21, and the excitation coil 21 generates an excitation magnetic field
Wherein H0F is the magnetic field frequency for exciting the amplitude of the magnetic field in the coil 21The ratio of the total weight of the particles,
the magnetic field phase. The signal generator 2b outputs an alternating current
Wherein I0Is the bias current amplitude in the hall sensor 22, f' is the current frequency,
' is the current phase. The sample to be tested is induced to generate a magnetic moment M ═ chi H with the same frequency under the action of an excitation magnetic field H, wherein chi is the sample magnetic susceptibility. The magnetic field generated by the magnetic moment acts on the Hall sensor to generate Hall voltage. Hall voltage VHallThe relationship with the sample magnetic susceptibility χ, the excitation magnetic field H, and the current I on the hall sensor is as follows:
the signal generator 2c outputs an alternating signal with a frequency f-f '(or f + f') to the reference signal input of the lock-in amplifier 23, whereby the lock-in amplifier 23 measures the hall voltage VHallThe f-f 'difference frequency component (or f + f' sum frequency component) in (a), which is proportional to the sample magnetic susceptibility χ.
The Hall sensor 22 of the invention can detect the magnetic field generated by the sample with small magnetic moment, thereby improving the measurement precision; the Hall voltage output by the Hall sensor 22 is in direct proportion to the magnetic field generated by the magnetic moment of the sample and is irrelevant to the measurement frequency, so that alternating current magnetic susceptibility data with high signal-to-noise ratio can be obtained even in a low-frequency region; the Hall sensor is equivalent to a mixer in the measurement, the frequency directly measured by the phase-locked amplifier is the difference frequency or the sum frequency of the alternating magnetic field of the exciting coil and the current of the Hall sensor by using the coherent double-alternating current measurement method, the frequency of the alternating magnetic field of the exciting coil is avoided, and the problem that the alternating magnetic field in a high-frequency area induces a larger background signal in a measurement circuit in a detection coil alternating current magnetic susceptibility device based on Faraday's law of electromagnetic induction is effectively solved. More importantly, because the current of the Hall sensor, the current for generating the alternating current magnetic field and the reference signal of the phase-locked amplifier come from the same clock, the phase-locked amplifier carries out coherent detection on the current and the magnetic field signal, incoherent noise is filtered out, and the signal-to-noise ratio is further improved.
Based on the above measurement principle, in order to improve the accuracy, the voltage output terminals 223 and 224 of the hall sensor 22 are arranged on the same straight line perpendicular to the bias current direction in the current input terminals 221 and 222, so that the influence of the resistance division of the hall sensor 22 in the bias current direction on the measurement of the hall voltage is reduced or avoided.
A method of measuring the alternating-current magnetic susceptibility of a magnetic sample using the alternating-current magnetic susceptibility measuring apparatus 2 of the present embodiment will be briefly described below.
First, a 0.2 mm by 0.4 mm monomolecular magnet [ Mn ] was prepared12O12(CH3COO)16(H2O)4](Mn12Ac) single crystal sample 24. A single crystal sample 24 to be measured is adhered to the surface of the Hall sensor 22 through low-temperature vacuum silicone grease, wherein one end of the single crystal sample 24 is fixed at the cross of the Hall sensor made by using a GaAs/AlGaAs heterojunction. Fixing the single crystal sample 24 and the hall sensor 22 together on the positioning plane 252 of the support 25, placing the support 25 inside the exciting coil 21, optionally filling adhesive between the contact surfaces of the two to prevent the exciting coil 21 from sliding relative to the support 25, further ensuring that the bias current direction in the hall sensor 22 is parallel to the magnetic field direction inside the exciting coil 21, and finally placing the ac magnetic susceptibility measuring device 2 in the sample chamber of a physical property measuring instrument (PPMS) to control the measuring temperature of the sample 24 to be measured.
The same clock trigger 2d selected by the signal generators 2a, 2b, 2c is the internal clock of the signal generator 2a, with a frequency of 10 MHz. The peak-to-peak voltage output by the signal generator 2a is 10 v, the frequency f is 13hz, the excitation current in the excitation coil 21 is 3.6mA, and the excitation magnetic field is about 12 gauss. The signal generator 2b outputs a voltage peak to peak of 10 volts at a frequency f' of 8.125Hz, at which time the current bias in the hall sensor 22 is 3.6 ua. The peak-to-peak voltage output by signal generator 2c is 2 volts and the frequency is 4.875Hz (i.e., f-f'). The parameters of the lock-in amplifier 23 are set as follows: the time constant is 3 seconds, the measuring range is 20 muV, the signal is selected to be in an XY mode, and the reference signal is selected to be an external reference signal source.
The real and imaginary values of the output signal of the lock-in amplifier 23 are recorded by the computer 26, so that the information of the real and imaginary parts of the ac susceptibility of the measured sample at the frequency of 13Hz can be obtained. By changing the temperature in the sample cavity of the PPMS, information of the real part and the imaginary part of the alternating-current magnetic susceptibility of the sample 24 to be measured at different temperatures is obtained.
Fig. 5 and 6 show graphs of the real part and the imaginary part of the ac magnetic susceptibility at frequencies of 3Hz, 13Hz, 33Hz, 77Hz, and 133Hz, respectively, of the above sample measured using the ac magnetic susceptibility measuring device 2, respectively, as a function of temperature. Compared with the prior art that the alternating current magnetic susceptibility is measured by using a coil based on the Faraday's law of electromagnetic induction (shown in figures 2 and 3), the alternating current magnetic susceptibility measuring device 2 of the embodiment effectively improves the measurement precision and the signal-to-noise ratio, and obtains low-frequency alternating current magnetic susceptibility data with excellent signal-to-noise ratio.
The invention is not limited to measuring the alternating-current magnetic susceptibility of the monomolecular magnet, and can also measure the alternating-current magnetic susceptibility of other magnetic materials.
In other embodiments of the present invention, the hall sensor may be made of any other material having a significant hall effect.
In other embodiments of the present invention, the exciting coil 21 is not limited to be wound in a solenoid shape as long as the magnetic field intensity distribution inside thereof is made uniform. Similarly, the holder 25 of the present invention is not limited to a semi-cylindrical shape, but may be other shapes configured to have a positioning plane parallel to the direction of the excitation magnetic field.
In other embodiments of the invention, the clock output of any one of the signal generators 2a, 2b, 2c is connected to the clock inputs of the other two signal generators.
In other embodiments of the invention, the frequency of the ac excitation output by signal generator 2c is the sum of the frequencies of the ac excitations output by signal generator 2a and signal generator 2 b.
Although the present invention has been described by way of preferred embodiments, the present invention is not limited to the embodiments described herein, and various changes and modifications may be made without departing from the scope of the present invention.
Claims (8)
1. An alternating current magnetic susceptibility measurement apparatus, comprising:
an excitation coil for generating an excitation magnetic field in an energized state;
the Hall sensor is positioned in the exciting coil and comprises two current input ends and two voltage output ends, and the direction of bias current in the two current input ends is parallel to the direction of an exciting magnetic field in the exciting coil;
the output end of the first signal generator is connected to two ends of the exciting coil and is used for providing alternating current excitation of a first frequency for the exciting coil;
the output end of the second signal generator is connected to the two current input ends of the Hall sensor and is used for providing alternating current excitation of a second frequency for the Hall sensor;
the signal input end of the phase-locked amplifier is connected to the two voltage output ends of the Hall sensor; and
a third signal generator that outputs an ac stimulus at a third frequency to a reference signal input of the lock-in amplifier, the third frequency being equal to a difference or a sum of the first frequency and the second frequency.
2. The ac magnetic susceptibility measurement device of claim 1, wherein the hall sensor is cross-shaped, and two current input ends of the hall sensor are oppositely arranged and parallel to the direction of the excitation magnetic field.
3. The ac magnetic susceptibility measurement device according to claim 2, wherein the two voltage outputs of the hall sensor are arranged on the same straight line perpendicular to the bias current in the two current inputs.
4. The ac magnetic susceptibility measurement device of claim 2, wherein the hall sensor has an adhesive at the cross for fixing the magnetic sample.
5. The ac magnetic susceptibility measurement device of claim 1, wherein the excitation coil is solenoid-shaped.
6. The ac magnetic susceptibility measurement device according to claim 5, further comprising a support made of a non-magnetic material, the support being located inside the excitation coil, the support having a positioning plane parallel to the direction of the excitation magnetic field, the hall sensor being disposed on the positioning plane.
7. The ac magnetic susceptibility measurement device of claim 1, wherein the first, second and third signal generators output continuously adjustable in frequency and have a common clock trigger.
8. A measuring method based on the ac magnetic susceptibility measuring apparatus according to any one of claims 1 to 7, characterized by comprising the steps of:
step 1), adhering a sample to be detected to an induction area of the Hall sensor;
step 2), placing the Hall sensor inside the exciting coil to enable the direction of the bias current of the Hall sensor to be parallel to the direction of an exciting magnetic field inside the exciting coil;
step 3), controlling the temperature of the sample to be detected to be a preset temperature value;
step 4), adjusting the output frequency of the first signal generator to provide alternating current excitation of a first frequency for the exciting coil, adjusting the output frequency of the second signal generator to provide alternating current excitation of a second frequency for the Hall sensor, and adjusting the output frequency of the third signal generator to provide alternating current excitation of a third frequency for the reference signal input end of the phase-locked amplifier;
and 5) measuring the voltage of the voltage output end of the Hall sensor by using the lock-in amplifier.
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| CN110579729A (en) * | 2019-10-10 | 2019-12-17 | 北京飞斯科科技有限公司 | alternating current magnetic susceptibility measuring device and method |
| CN114264555B (en) * | 2021-12-29 | 2023-09-12 | 中国科学院合肥物质科学研究院 | Device and method for measuring strain distribution state of superconducting wire |
| CN115718273B (en) * | 2022-11-18 | 2024-04-19 | 华中科技大学 | Device for measuring object magnetic susceptibility based on magnetic induction intensity and measuring method thereof |
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