Magnetic field control device and magnetic field control method for magnetic force microscope

Abstract

According to the magnetic field control device and the magnetic field control method for the magnetic force microscope provided by the invention, the distance between a magnet and a sample table is adjusted through a lifting mechanism between a displacement table base and a piezoelectric table; the lifting mechanism comprises a connecting base, and the connecting base comprises a connecting plate connected with the displacement table base, a boss arranged on the connecting plate and extending into the piezoelectric station, and a containing cavity formed in the boss. A screw rod is rotationally arranged between the connecting plate and the boss, a belt wheel is arranged at one end of the screw rod, the other end of the screw rod is connected with a moving block, and the moving block is slidably arranged in the containing cavity; a belt wheel drives a screw rod and drives a moving block to lift, a driving source is allowed to be arranged on the side face, a boss extends into a piezoelectric station, the requirement for the height of a displacement table is lowered, and the structure is compact; and the screw rod is rotatably arranged between the connecting plate and the boss, so that sealing at the rotary connecting position is facilitated, and a magnet box does not need to be arranged.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of atomic force microscope, and particularly relates to a magnetic field control device and a magnetic field control method for a magnetic force microscope. BACKGROUND

[0002] An atomic force microscope (AFM) detects the micro properties of a sample by moving a probe on the surface of the sample and detecting the interaction force between the probe and the sample by optical lever technology. On this basis, a magnetic force microscope can detect the magnetism of a sample by using a magnetic probe and detecting the interaction force between the magnetic probe and the sample. In some cases, it is necessary to place the sample in a magnetic field to detect the magnetic characteristics of the sample under the influence of the magnetic field and to explore the magnetic properties of the sample.

[0003] In the prior art, the aforementioned requirement is mainly achieved by setting an electromagnet to generate a magnetic field at the position of the sample to be detected. However, the volume of the existing electromagnet is usually large, which is not conducive to the miniaturization of the atomic force microscope. At the same time, the large electromagnet will interfere with the position adjustment and placement of the sample, affecting the use efficiency. SUMMARY

[0004] To solve the above problems, the present application provides a magnetic field control device and a magnetic field control method for a magnetic force microscope. The lifting mechanism between the displacement table base and the piezoelectric table realizes the adjustment of the distance between the magnet and the sample table, and the position of the sample does not need to be adjusted when the electromagnetic field of the sample is changed. The driving screw drives the lifting of the moving block, which allows the driving device to be arranged on the outside, reduces the requirement for the height of the displacement table, and has a compact structure. The rotation of the screw is arranged between the connecting plate and the boss, which facilitates sealing at the rotating connection position and does not need to set a magnet box.

[0005] To achieve the above purpose, in a first aspect, the present application provides a magnetic field control device for a magnetic force microscope, which adopts the following technical scheme: A magnetic field control device for a magnetic force microscope, comprising a displacement table base, a piezoelectric table, a sample table arranged on the piezoelectric table, a lifting mechanism arranged between the displacement table base and the piezoelectric table, and a magnet arranged on the lifting mechanism. The lifting mechanism comprises a connecting seat, the connecting seat comprises a connecting plate connected with the displacement table base, a boss arranged on the connecting plate and extending into the piezoelectric table, and a containing cavity opened in the boss; a screw rod is rotationally arranged on the connecting seat and extends into the containing cavity; one end of the screw rod is in transmission connection with the driving device, and the other end is provided with a moving block capable of moving along the axial direction of the screw rod under the driving of the screw rod; the moving block is slidingly arranged in the containing cavity; the magnet is arranged at the end of the moving block away from the pulley.

[0006] Further, a sealing bearing is arranged at one end of the containing cavity close to the connecting plate; the screw rod is rotationally arranged on the connecting seat through the sealing bearing.

[0007] Further, the sample table comprises a connecting part connected with the piezoelectric table, and a placing table arranged on the connecting part, wherein the placing table is provided with a magnet containing space capable of containing the magnet.

[0008] Further, a sliding groove is opened in the side wall of the containing cavity, and a sliding rod is arranged on the moving block and slidingly arranged in the sliding groove.

[0009] Further, the driving device is arranged outside the connecting seat.

[0010] To achieve the above purpose, in the second aspect, the application further provides a magnetic field control method for a magnetic force microscope, which adopts the following technical scheme: A magnetic field control method for a magnetic force microscope uses the magnetic field control device for a magnetic force microscope as described in the first aspect, and comprises: rotating the screw rod by the driving device to realize the axial movement of the moving block along the screw rod, thereby driving the magnet to ascend and descend; the driving device is a motor, the driving device is in transmission connection with the screw rod through a transmission belt, when adjusting the ascending and descending of the magnet, the number of revolutions of the actual control motor is obtained by correcting the number of revolutions of the theoretical control motor according to the environmental temperature; specifically, the number of revolutions of the actual control motor is equal to the product of the number of revolutions of the theoretical control motor and the correction coefficient, and the correction coefficient is determined by the weight sum of the length change rate of the transmission belt and the change rate of the environmental temperature.

[0011] To achieve the above purpose, in the third aspect, the application further provides a magnetic field control method for a magnetic force microscope, which adopts the following technical scheme: A magnetic field control method for a magnetic force microscope uses the magnetic field control device for a magnetic force microscope as described in the first aspect, and comprises: determining the correlation between the magnetic field at the sample table and the ascending and descending position of the magnet through detection; setting the measured sample on the sample table, and adjusting the ascending and descending position of the magnet according to the magnetic field requirement of the measured sample.

[0012] Further, the magnet is an electromagnet or an excitation coil, and the method further comprises: determining the relationship between the magnetic field at the sample stage and the current of the magnet by detection; and setting the sample to be measured on the sample stage, and adjusting the current of the magnet according to the magnetic field requirement of the sample to be measured.

[0013] Further, at least one of the position of the magnet and the current of the magnet is adjusted according to at least one of the relationship between the magnetic field at the sample stage and the lifting position of the magnet and the relationship between the magnetic field at the sample stage and the current of the magnet.

[0014] Further, the relationship between the magnetic field at the sample stage and the lifting position of the magnet is detected by adjusting the lifting position of the magnet to one or more preset height positions and measuring the magnetic field parameters at each position of the sample stage when the magnet is at the different preset height positions, so as to obtain a set of relationships between the preset height positions, the positions of the sample stage and the magnetic field parameters.

[0015] Further, the sample to be measured is set on the sample stage, and the lifting position of the magnet is adjusted according to the magnetic field requirement of the sample to be measured, which comprises: setting the sample to be measured on the sample stage; detecting the position of the magnet; adjusting the lifting position of the magnet according to the relative position relationship between the magnet and the sample to be measured.

[0016] Further, the positions of the magnet include a lowest position, a highest position and a plurality of preset positions between the lowest position and the highest position.

[0017] In order to achieve the above-mentioned purpose, in a fourth aspect, the application further provides a scanning probe microscope, which adopts the following technical scheme: A scanning probe microscope uses the magnetic field control device for a magnetic force microscope as described in the first aspect.

[0018] Compared with the prior art, the application has the following beneficial effects: In the present invention, the distance between the magnet and the sample stage is adjusted by the lifting mechanism between the displacement stage base and the piezoelectric stage, and the adjustment and control of the sample magnetic field are achieved, and the position of the sample does not need to be adjusted when the sample electromagnetic field is changed; wherein, the lifting mechanism includes a connecting seat, the connecting seat includes a connecting plate connected to the displacement stage base, a boss arranged on the connecting plate and extending into the piezoelectric stage, and an accommodating cavity opened in the boss; a screw is rotatably arranged between the connecting plate and the boss, one end of the screw is transmission-connected to the driving device, and the other end is connected to a moving block, and the moving block is slidingly arranged in the accommodating cavity; the screw is driven by the driving device to drive the moving block to rise and fall, which allows the driving device to be arranged on the outside, reduces the requirement for the height of the displacement stage, and has a compact structure; and the screw is rotatably arranged between the connecting plate and the boss, which is convenient for sealing at the rotating connection position, and does not require a magnet box. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings constituting a part of the specification of this embodiment are used to provide a further understanding of this embodiment. The schematic embodiments and descriptions of this embodiment are used to explain this embodiment and do not constitute an improper limitation on this embodiment.

[0020] Figure 1 Schematic diagram of the structure of the translation stage according to embodiment 1 of the present invention; Figure 2 1 is an exploded view of the translation stage according to embodiment 1 of the present invention; Among them, 1. Translation stage base; 2. Pressure stage; 3. Sample stage; 301. Connecting part; 302. Placement stage; 303. Magnet accommodating space; 4. Magnet; 5. Lifting mechanism; 501. Connecting seat; 5011. Connecting plate; 5012. Boss; 5013. Accommodating cavity; 5014. Slide groove; 5015. Round table; 5016. Sealed bearing; 502. Screw; 503. Pulley; 504. Moving block; 505. Slide rod; 506. Transmission belt. DETAILED DESCRIPTION

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs.

[0023] Example 1: like Figure 1 As shown, this embodiment provides a magnetic field control device for a magnetic force microscope, including a translation stage base 1, a piezoelectric stage 2, a sample stage 3, a magnet 4 and a lifting mechanism 5.

[0024] The displacement table base 1 can adopt a metal plate mechanism; two driving devices perpendicular to each other can be arranged on the displacement table base 1 to realize the movement of the displacement table base 1 and the entire displacement table on the horizontal plane. The driving device can adopt a telescopic rod, a linear motor, or other devices capable of driving the displacement table base 1 and the entire displacement table to move on the horizontal plane.

[0025] The piezoelectric table 2 is provided with a containing hole capable of containing the boss 5012, and other parts and structures of the piezoelectric table 2 can be realized by conventional technology, which will not be described in detail here.

[0026] The sample table 3 is used for placing a sample, and is arranged on the piezoelectric table 2 by bolt connection, welding or other connection methods; the sample table 3 comprises a connecting part 301, a placing table 302 and a magnet containing space 303. The connecting part 301 and the placing table 302 can be integrally formed or connected by welding, and the connecting part 301 is used to connect the piezoelectric table 2. The placing table 302 is provided with a magnet containing space 303, which can be used to contain the magnet 4, and the arrangement of the magnet containing space 303 shortens the distance between the magnet 4 and the sample.

[0027] The magnet 4 provides a magnetic field for the sample, and can include at least one of an excitation coil, an electromagnet and a permanent magnet to generate a corresponding magnetic field. The magnet 4 is installed on the top of the lifting mechanism 5, and the distance between the magnet 4 and the sample table 3 is adjusted by the lifting mechanism 5 to adjust the size of the magnetic field in which the measured object is located.

[0028] The lifting mechanism 5 comprises a connecting seat 501, a screw rod 502, a pulley 503, a moving block 504, a sliding rod 505 and a transmission belt 506.

[0029] The connecting seat 501 comprises a connecting plate 5011, a boss 5012, a containing cavity 5013, a sliding groove 5014, a circular table 5015 and a sealing bearing 5016. The connecting plate 5011 is a plate-shaped mechanism, which is arranged between the displacement table base 1 and the piezoelectric table 2, and is connected with the displacement table base 1 and the piezoelectric table 2 on both sides by bolt connection or other connection methods; the connecting plate 5011 is provided with a space for containing the pulley 503 and the transmission belt 506.

[0030] The boss 5012 and the connecting plate 5011 can adopt an integral structure, or be connected by welding or the like. The boss 5012 is located in the accommodating hole in the piezoelectric platform 2, and the structure is compact. The mobile block 504 is arranged to slide in the accommodating cavity 5013; at least one sliding groove 5014 is formed in the side wall of the accommodating cavity 5013, and at least one sliding rod 505 is arranged on the outer wall of the mobile block 504, which is arranged to slide in the sliding groove 5014, thereby improving the stability of the movement of the mobile block 504 in the accommodating cavity 5013.

[0031] In the accommodating cavity 5013, a circular table 5015 is arranged at one end close to the connecting plate 5011, and a sealing bearing 5016 is arranged on the circular table 5015; the screw rod 502 is arranged to rotate on the connecting seat 501 through the sealing bearing 5016, thereby achieving sealing of the magnet 4 and avoiding the arrangement of a magnet box.

[0032] One end of the screw rod 502 is in driving connection with the driving device, and the other end of the screw rod 502 is connected with the mobile block 504 in a threaded connection manner. In work, the driving device drives the screw rod 502 to rotate, thereby driving the mobile block 504 to move in the accommodating cavity 5013 and changing the distance between the magnet 4 and the sample platform.

[0033] The transmission mode between the driving device and the screw rod 502 can adopt gear, threaded screw rod, belt transmission, pneumatic, hydraulic transmission and the like. As a feasible implementation manner, the driving device and the screw rod 502 are arranged in a belt transmission, specifically, the pulley 503 is connected with one end of the screw rod 502, the pulley 503 is in driving connection with the driving device through the transmission belt 506, the driving device drives the transmission belt 506 to rotate, thereby driving the pulley 503 to rotate and driving the screw rod 502 to rotate.

[0034] Embodiment 2: The embodiment provides a magnetic field control method for a magnetic force microscope, which uses the magnetic field control device for the magnetic force microscope as described in embodiment 1, and includes: driving the mobile block 504 to move by rotating the screw rod 502, driving the magnet 4 to move by the mobile block 504, changing the distance between the magnet 4 and the sample platform 3, and adjusting the magnetic field size in which the sample on the sample platform 3 is located.

[0035] In some embodiments, in the transmission process of the transmission belt 506 and the pulley 503, and the transmission process of the screw rod 502 and the mobile block 504, the transmission belt 506 and the pulley 503 will appear sliding phenomenon, and the transmission error will exist between the screw rod 502 and the mobile block 504.

[0036] Specifically, in the process of belt transmission, due to the elastic deformation of the transmission belt 506, elastic sliding phenomenon will occur, the belt will be elastically stretched due to the tension, resulting in the speed of the driven wheel not completely synchronized with the driving wheel, and this elastic sliding is one of the main reasons for the inaccuracy of the transmission ratio. With the increase of the length L of the transmission belt 506, the elastic deformation becomes larger, and the transmission is more affected. In addition, the change of the environmental temperature T will also affect the accuracy of the transmission belt 506; the increase of the environmental temperature T may cause the performance of the material of the transmission belt 506 to change, such as the decrease of the elastic modulus, thermal expansion, etc., which may cause the fluctuation of the transmission ratio. The transmission of the screw rod 502 and the moving block 504 is relatively stable compared with the transmission of the transmission belt 506, so the transmission error temperature caused by the transmission belt 506 is considered in the embodiment: Assuming that the theoretical control motor rotation number A, after passing through the transmission belt 506, the pulley 503, the screw rod 502 and the moving block 504, is related to the lifting H of the magnet 4 as follows: A=aH, wherein a is the transmission coefficient. It can be understood that theoretically, the control motor rotates one circle corresponding to the lifting H of the magnet 4, which has a one-to-one correspondence; wherein the transmission coefficient is responsible for the effect of the dimension conversion of the lifting and the number of rotation circles in addition to realizing the corresponding relationship in the numerical value.

[0037] The transmission belt 506 rotates under the drive of the motor, thereby driving the pulley 503 to rotate, the pulley 503 drives the screw rod 502 to rotate, thereby driving the moving block 504 to move, and the moving block 504 drives the magnet 4 to lift; when adjusting the lifting of the magnet 4, the influence of the length of the transmission belt 506 and the environmental temperature on the transmission ratio accuracy is considered, and the theoretical control motor rotation number is corrected to obtain the actual control motor rotation number. The actual control motor rotation number is equal to the product of the theoretical control motor rotation number A and the correction coefficient (1+b(L-L0) / L0+c(T-T0) / T0); the correction coefficient is determined by the weight of the length change rate (L-L0) / L0 and the environmental temperature change rate (T-T0) / T0 of the transmission belt 506. When the length L of the transmission belt 506 is less than the preset length L0, the right coefficient b corresponding to the length change rate of the transmission belt 506 is equal to zero; when the environmental temperature T is less than the preset temperature T0, the right coefficient c corresponding to the environmental temperature change rate is equal to zero. In actual control, the relationship between the actual control motor rotation number A1 and the lifting H of the magnet 4 is as follows: A1=A(1+b(L-L0) / L0+c(T-T0) / T0); wherein b and c are preset parameters, which can be determined by experimental methods; when L-L0 is less than zero, b is equal to zero; when T-T0 is less than zero, c is equal to zero; L is the length L of the transmission belt 506; L0 is a preset standard length value, which can be obtained by experimental methods; T is the environmental temperature; T0 is a preset standard temperature value, such as room temperature.

[0038] In this embodiment, the influence of the length L of the transmission belt 506 and the ambient temperature T on the transmission ratio accuracy is considered, the theoretical control motor rotation number A is corrected to obtain the actual control motor rotation number A1, and the control accuracy is ensured; and the magnetic field control accuracy is ensured.

[0039] Embodiment 3 In some other embodiments, the magnet 4 can be a magnet and / or a coil, and thus, the magnet, the coil, and / or the magnet+coil can be set alone according to the test requirements to generate a magnetic field corresponding to the test requirements. Correspondingly, the structure can be manually replaced by the coil or the magnet or the magnet+coil, or the magnet+coil can be directly set at the original position of the magnet. When the coil+ magnet is required to jointly generate a magnetic field, the coil can be powered. Alternatively, the magnet+coil can be set in the following two ways: one is that the coil can be sleeved on the magnetic pole of the magnet, that is, the relative position of the coil and the magnet is fixed, and the distance between the coil and the magnet and the sample table is jointly adjusted; the other is that the coil and the magnet are independently adjusted by another set of screw rods or other components. For example, the magnet can be a ring magnet, and the coil can be displaced up and down from the through hole in the middle of the ring magnet. For one of the implementations of the independent adjustment of the coil and the magnet, the screw rod is made into a cylindrical tube, the magnet wall of the circular ring magnet is arranged on the annular upper tube wall of the cylindrical tube, a smaller diameter cylindrical or circular tube can be further sleeved in the cylindrical tube, and the coil is correspondingly arranged on the upper surface or the annular upper tube wall, so that the coil can be displaced up and down in the outermost cylindrical tube. As for the power supply line of the coil, the power supply line can be pre-buried in the cylindrical tube or run in the inner surface of the cylindrical tube.

[0040] The embodiment provides a magnetic field control method for a magnetic force microscope, and uses the magnetic field control device for the magnetic force microscope as described in Embodiment 1, and the method comprises the following steps: determining the correlation between the magnetic field at the sample table 3 and the lifting position of the magnet 4 through detection; and setting the sample to be tested on the sample table 3, and adjusting the lifting position of the magnet 4 according to the magnetic field requirement of the sample to be tested.

[0041] Optionally, the detection of the correlation between the magnetic field at the sample table 3 and the lifting position of the magnet 4 comprises the following steps: adjusting the magnet 4 to one or more preset height positions, and measuring the magnetic field parameters at each position of the sample table 3 when the magnet 4 is at different preset height positions, so as to obtain a set of correlations between the preset height positions, the positions of the sample table 3, and the magnetic field parameters.

[0042] In some cases, the magnet 4 can be an electromagnet or an excitation coil, and correspondingly, the method further comprises the following steps: determining the correlation between the magnetic field at the sample table 3 and the current of the magnet 4 through detection; and setting the sample to be tested on the sample table 3, and adjusting the current of the magnet 4 according to the magnetic field requirement of the sample to be tested.

[0043] In some cases, the position or current of the magnet 4 can be adjusted according to at least one of the relationship between the magnetic field at the sample stage 3 and the position of the magnet 4, and the relationship between the magnetic field at the sample stage 3 and the current of the magnet 4.

[0044] Optionally, the sample to be measured is placed on the sample stage 3, and the position of the magnet 4 is adjusted according to the magnetic field requirement of the sample to be measured, including: placing the sample to be measured on the sample stage 3; detecting the position of the magnet 4, which can be converted according to the number of rotations of the motor, or a position sensor can be additionally provided, which will not be described in detail here; adjusting the position of the magnet 4 according to the relative position relationship between the magnet 4 and the sample to be measured.

[0045] Optionally, the positions of the magnet 4 include a lowest position, a highest position, and a plurality of positions between the lowest position and the highest position, and the lowest position and the highest position are determined by the movement limits of the moving block 504.

[0046] Embodiment 4 The embodiment provides a scanning probe microscope, which uses the magnetic field control device for a magnetic force microscope as described in Embodiment 1.

[0047] The above only describes the preferred embodiments of the present embodiment and is not intended to limit the present embodiment. The present embodiment can have various modifications and changes for those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present embodiment shall be included in the protection scope of the present embodiment.

Claims

1. A magnetic field control device for a magnetic force microscope, characterized in that: It comprises a displacement stage base (1), a piezoelectric stage (2), a sample stage (3) arranged on the piezoelectric stage (2), a lifting mechanism (5) arranged between the displacement stage base (1) and the piezoelectric stage (2), and a magnet (4) arranged on the lifting mechanism (5); The lifting mechanism (5) comprises a connecting seat (501), the connecting seat (501) comprising a connecting plate (5011) connected to the displacement stage base (1), a boss (5012) arranged on the connecting plate (5011) and extending into the pressure stage (2), and an accommodating cavity (5013) provided in the boss (5012); a screw rod (502) is rotatably arranged on the connecting seat (501), and the screw rod (502) extends into the accommodating cavity (5013); one end of the screw rod (502) is transmission-connected to a driving device, and the other end is provided with a moving block (504), the moving block (504) can move along the axial direction of the screw rod (502) under the drive of the screw rod (502), and the moving block (504) is slidably arranged in the accommodating cavity (5013); the magnet (4) is arranged at one end of the moving block (504) away from the pulley (503).

2. A magnetic field control device for a magnetic force microscope according to claim 1, characterized in that: A sealing bearing (5016) is provided in the accommodating cavity (5013) on a side close to the connecting plate (5011); the screw (502) is rotatably arranged on the connecting seat (501) via the sealing bearing (5016).

3. The magnetic field control device for a magnetic force microscope according to claim 1, characterized in that: The sample stage (3) comprises a connecting portion (301) connected to the piezoelectric stage (2), and a placement table (302) arranged on the connecting portion (301), wherein a magnet accommodating space (303) capable of accommodating a magnet (4) is provided in the placement table (302).

4. The magnetic field control device for a magnetic force microscope according to claim 1, characterized in that: A sliding groove (5014) is provided on the side wall of the accommodating cavity (5013), and a sliding rod (505) is provided on the moving block (504). The sliding rod (505) is slidably arranged in the sliding groove (5014).

5. The magnetic field control device for a magnetic force microscope according to claim 1, characterized in that: The driving device is arranged outside the connecting seat (501).

6. A magnetic field control method for a magnetic force microscope, characterized in that: A magnetic field control device for a magnetic force microscope as described in any one of claims 1 to 5 is used, comprising: determining the correlation between the magnetic field at the sample stage (3) and the lifting position of the magnet (4) through detection; placing the sample to be measured on the sample stage (3), and adjusting the lifting position of the magnet (4) according to the magnetic field requirement of the sample to be measured.

7. The magnetic field control method for a magnetic force microscope according to claim 6, wherein: The magnet (4) is an electromagnet or an excitation coil, and the method further comprises: determining the correlation between the magnetic field at the sample stage (3) and the current of the magnet (4) by detection; placing the sample to be measured on the sample stage (3), and adjusting the current of the magnet (4) according to the magnetic field requirement of the sample to be measured.

8. The magnetic field control method for a magnetic force microscope according to claim 7, wherein: According to at least one of the correlation between the magnetic field at the sample stage (3) and the lifting position of the magnet (4), and the correlation between the magnetic field at the sample stage (3) and the current of the magnet (4), at least one of the lifting position and the current of the magnet (4) is adjusted.

9. The magnetic field control method for a magnetic force microscope according to claim 6, wherein: Detecting the correlation between the magnetic field at the sample stage (3) and the lifting position of the magnet (4) includes: adjusting the magnet (4) to lift to one or more preset height positions, and measuring the magnetic field parameters at each position of the sample stage (3) when the magnet (4) is at different preset height positions, so as to obtain a set of correlations between the preset height positions, each position of the sample stage (3) and the magnetic field parameters.

10. The magnetic field control method for a magnetic force microscope according to claim 6, wherein: The sample to be tested is placed on the sample stage (3), and the position of the magnet (4) is adjusted according to the magnetic field requirements of the sample to be tested, including: The sample to be tested is placed on the sample stage (3); detecting the position of the magnet (4); The lifting position of the magnet (4) is adjusted according to the relative position relationship between the magnet (4) and the sample to be measured.

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