CN116047379A - A Synchronous Measurement System of Dynamic Magnetic Domain Imaging and Local Hysteresis Loop - Google Patents

Abstract

The invention improves a local magnetization vector signal measurement method, and discloses a dynamic magnetic domain imaging and local hysteresis loop synchronous measurement system and a magnetic domain image processing method, wherein the magnetic domain imaging synchronous measurement system comprises a magneto-optical Kerr microscopic imaging optical path, a local Kerr loop measurement optical path, a sample and magnetic field control system and an electric control translation switching control system, and a computer processing method for optimizing magnetic domain structure imaging patterns; the invention designs a set of optical system capable of simultaneously measuring magnetic domain structures and local hysteresis loops of different magnetization vectors of ferromagnetic materials based on magneto-optical Kerr effect principle, phase lock amplification technology and image processing technology.

Description

A Synchronous Measurement System of Dynamic Magnetic Domain Imaging and Local Hysteresis Loop

technical field

The invention relates to the field of magnetism, in particular to a dynamic magnetic domain imaging and local hysteresis loop synchronous measurement system.

Background technique

After the magnetic domain theory was proposed, magnetism developed rapidly. According to previous practical experiments and proposed theoretical models, magnetic phenomena such as magnetization intensity, magnetization curve, and magnetostriction can be explained using magnetic domain theory. It is very important to improve the magnetic properties of magnetic materials.

Magnetic Domain Hypothesis: On the microscopic scale, ferromagnetic materials can be divided into many continuous and adjacent micro-regions according to the direction of atomic magnetic moments. When the material is demagnetized as a whole, the direction of atomic magnetic moments in each micro-region is random. Therefore, after the magnetic moments of each tiny region are canceled out, the overall magnetic moment of the material is zero, so the material as a whole is not magnetic to the outside, and each tiny region divided according to the orientation of the atomic magnetic moment is called a magnetic domain.

Magnetic domain is an integral part of the microscopic structure of magnetic materials, which links the basic physical properties of materials with their macroscopic properties and applications. The macroscopic magnetic properties exhibited by magnetic materials can be explained by the microscopic magnetic properties of magnetic domains.

Magnetic domain imaging provides an intuitive way to explore the local magnetism and domain wall dynamics of ferromagnetic materials, and the magnetic domain imaging technology using the magneto-optical Kerr effect - magneto-optical Kerr microscopy, can non-destructively and effectively observe the magnetic field domain structure.

However, in the current field of magnetism, in order to measure the magnetic domain structure and local hysteresis loops of different magnetization vectors, it is necessary to change the relative positions of the sample, detection device, light source and microscope, and measure each different magnetization vector separately. The process is extremely cumbersome. . In addition, the existing technology is difficult to accurately measure information such as local hysteresis loops while obtaining the magnetic domain structure image. In order to solve these problems, a dynamic magnetic domain imaging and local hysteresis loop synchronous measurement system and image processing method are proposed.

Contents of the invention

The present invention overcomes the deficiencies of the prior art, and the present invention makes the following improvements and optimizations for the above-mentioned shortcoming.

The purpose of the present invention is achieved through the following technical solutions:

Provides a dynamic magnetic domain imaging and local hysteresis loop synchronous measurement system, including magneto-optical Kerr microscopic imaging optical path, local Kerr loop measurement optical path, sample and magnetic field control system and electronically controlled translation switching control system ;

The magneto-optical Kerr microscopic imaging optical path includes an optical fiber (1), an optical fiber output end (2), a lens I (3), a diaphragm I (4), and a polarizer I placed sequentially and horizontally on the same horizontal line (5), lens II (6), diaphragm II (7), lens III (8), polarization maintaining beam splitter (10) and infinity system microscopic objective lens (11), the magneto-optic Kerr microscopic imaging The optical path also includes an optical filter II (13), a 1/4 wave plate (14), an analyzer (15) and a tube lens (16) placed in sequence on the right left of the polarization maintaining beam splitter (10);

The local Kerr loop measurement optical path includes a laser (18), an attenuation plate I (19), a diaphragm III (20), a polarizer II ( 21), stop IV (22), telephoto concave lens (44), dichroic mirror I (9) and dichroic mirror II (12), said dichroic mirror I (9) is located in lens III (8 ) and the polarization maintaining beam splitter (10), the dichroic mirror II (12) is located between the polarization maintaining beam splitter (10) and the filter II (13), the local Kerr loop The measurement optical path also includes chopper (23), attenuation plate II (24), diaphragm V (25), half-wave plate (26), optical filter I (27), lens IV (28), Diaphragm VI (29), Glan prism (30), reflection mirror (31).

Preferably, the sample and magnetic field control system includes a sample holder system and a magnetic field control system.

More preferably, the sample rack system includes a sample rack (40) and a sample (35), and the sample rack (40) includes a glass plate (42).

More preferably, the magnetic field control system includes an electromagnet group (36) and a linear Hall detector group (43).

Preferably, the electronically controlled translation switching control system includes a translation switching system and a measurement optical measurement system.

More preferably, the measurement optical measurement system includes a CMOS camera (17) positioned on the left side of the tube lens (16), a balanced photodetector (32) placed in parallel under the Glan prism (30) and the mirror (31) And a lock-in amplifier (33) and a computer (34) for measurement.

More preferably, the translation switching system includes an electronically controlled two-dimensional translation stage I (37) for carrying and controlling the displacement of the optical fiber (1) and the optical fiber output end (2), an electronically controlled two-dimensional translation stage I (37) for carrying and controlling the displacement of the laser (18). Two-dimensional translation stage II (38), electronically controlled two-dimensional translation stage III (39) for carrying and controlling the displacement of the balanced photodetector (32), five-dimensional adjustment stage for carrying and controlling the displacement of the sample holder (40) (41), the electric control roller type switching seat I (45) for carrying and switching the telephoto concave lens (44), and the electric control roller type switching seat II (46) for carrying and switching the filter II (13) ).

Preferably, the dichroic mirror II (12) has a very high transmittance to the optical fiber light source band, while maintaining a low transmittance to the laser light source band, and is used to realize the imaging of the local magnetic field based on the magnetic domain structure of the sample. Auxiliary visual selection of the measurement area for the hysteresis line.

More preferably, the electronically controlled two-dimensional translation stage I (37) and the electronically controlled two-dimensional translation stage II (38) of the translation switching control system can control the position of the mounted light source according to the needs of use, and are used to change the incident light on the sample surface. In order to achieve the adjustment of the poloidal Kerr and longitudinal Kerr signal components measured by magnetic domain imaging and local hysteresis loops, the purpose of flexibly switching the measured magnetization vector components is achieved.

Compared with the prior art, the present invention has the following advantages:

1. It can flexibly adjust the angle of the imaging and measuring the incident light, and then easily realize the adjustment of the polar Kerr and longitudinal Kerr signal components measured by the magnetic domain imaging and the local hysteresis loop, so as to achieve flexible switching of the measured magnetization vector weight purpose. It can solve the cumbersomeness of changing the optical path when switching the polar Kerr and longitudinal Kerr signal components during magnetic domain imaging and local hysteresis loop measurement.

2. It can simultaneously measure the magnetic domain structure imaging pattern and local hysteresis loop information, and realize the characterization of the local magnetic domain structure and hysteresis Kerr loop signal of magnetic materials based on dual light sources. The problem that the magnetic domain structure imaging pattern and the local hysteresis loop cannot be measured at the same time is solved.

3. Before the measurement of the local hysteresis loop, based on the selection of specific parameters of the dichroic mirror, the visual observation of the magnetic domain structure of the sample can be realized. The area for measuring the local hysteresis loop can be selected, and the size of the measurement area can be determined by The rotary switch lens can be adjusted flexibly. Solved the problems that the local hysteresis loop cannot be visualized to select points and the size of the measurement area is difficult to adjust.

4. The present invention uses a method for measuring the Kerr rotation angle using an optical balance bridge and lock-in amplification technology. The method has high detection sensitivity, can greatly suppress the influence of noise, and increase the signal-to-noise ratio of the detection result . The signal-to-noise ratio of the local loop Kerr signal is improved, and the measurement accuracy is improved.

5. The present invention proposes a computer processing method for optimizing the imaging pattern of the magnetic domain structure, which improves the contrast of the imaging pattern of the magnetic domain structure and realizes super-resolution restoration. Improved image contrast for magnetic domain imaging.

Description of drawings

The present invention is further described by using the accompanying drawings, but the embodiments in the accompanying drawings do not constitute any limitation to the present invention. For those of ordinary skill in the art, without paying creative work, other embodiments can also be obtained according to the following accompanying drawings Attached picture.

Fig. 1 is a schematic diagram of a dynamic magnetic domain imaging and local hysteresis loop synchronous measurement system provided by the present invention;

Fig. 2 is a kind of magnetic film sample holder schematic diagram provided by the present invention;

FIG. 3 is a flow chart of a processing procedure for optimizing a magnetic domain image provided by the present invention;

Fig. 4 is the magnetic domain structure image that the present invention collects on the FePt film surface;

Fig. 5 is the magnetic domain inversion process that the present invention observes on FePt film;

Fig. 6 is the local hysteresis loop measured on the FePt thin film of the present invention;

Labels in the figure: 1, optical fiber; 2, output end of optical fiber; 3, lens I; 4, aperture I; 5, polarizer I; 6, lens II; 7, aperture II; 8, lens III; 9, Dichroic mirror Ⅰ; 10. Polarization maintaining beam splitter; 11. Infinity system microscope objective lens; 12. Dichroic mirror Ⅱ; 13. Filter Ⅱ; 14. 1/4 wave plate; 15. Analyzer ;16. Tube lens; 17. CMOS camera; 18. Laser; 19. Attenuation film I; 20. Aperture III; 21. Polarizer II; 22. Aperture IV; 23. Chopper; 24. Attenuation film Ⅱ; 25. Aperture Ⅴ; 26. Half-wave plate; 27. Filter Ⅰ; 28. Lens Ⅳ; 29. Aperture Ⅵ; 30. Glan prism; 31. Mirror; 32. Balanced photodetector; 33. Lock-in amplifier; 34. Computer; 35. Sample; 36. Electromagnet group; 37. Electronically controlled two-dimensional translation stage I; 38. Electronically controlled two-dimensional translation stage II; 39. Electronically controlled two-dimensional translation stage III; 40. Sample holder; 41. Five-dimensional adjustment table; 42. Glass plate; 43. Linear Hall detector group; 44. Telephoto concave lens; 45. Electric control roller switch seat I; 46. Electric control roller switch seat II.

Detailed ways

A dynamic magnetic domain imaging and local hysteresis loop synchronous measurement system will be further described in detail below in conjunction with specific embodiments, these embodiments are only for the purpose of comparison and explanation, and the present invention is not limited to these embodiments.

In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "left", "right", "top", "bottom" etc. Orientation or positional relationship is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation of the present invention.

As shown in Figure 1, it includes a magneto-optical Kerr microscopic imaging optical path, a local Kerr loop measurement optical path, a sample and magnetic field control system, and an electronically controlled translation switching control system;

The magneto-optical Kerr microscopic imaging optical path includes an optical fiber (1), an optical fiber output end (2), a lens I (3), a diaphragm I (4), and a polarizer I placed sequentially and horizontally on the same horizontal line (5), lens II (6), diaphragm II (7), lens III (8), polarization maintaining beam splitter (10) and infinity system microscopic objective lens (11), the magneto-optic Kerr microscopic imaging The optical path also includes an optical filter II (13), a 1/4 wave plate (14), an analyzer (15) and a tube lens (16) placed in sequence on the right left of the polarization maintaining beam splitter (10);

The local Kerr loop measurement optical path includes a laser (18), an attenuation plate I (19), a diaphragm III (20), a polarizer II ( 21), stop IV (22), telephoto concave lens (44), dichroic mirror I (9) and dichroic mirror II (12), said dichroic mirror I (9) is located in lens III (8 ) and the polarization maintaining beam splitter (10), the dichroic mirror II (12) is located between the polarization maintaining beam splitter (10) and the filter II (13), the local Kerr loop The measurement optical path also includes chopper (23), attenuation plate II (24), diaphragm V (25), half-wave plate (26), optical filter I (27), lens IV (28), Diaphragm VI (29), Glan prism (30), reflection mirror (31).

The chopper (23) chops and modulates the light entering the balanced photodetector (32). In this embodiment, the chopper (23) is placed directly under the dichroic mirror II (12).

Description of the optical path of magneto-optical Kerr microscopic imaging: Monochromatic light is transmitted through the optical fiber (1) to the output end of the optical fiber (2) at a lower divergence angle, and then focused to the diaphragm I (4) through the lens I (3) for further imaging. Stray light is filtered out to limit the aperture, and then becomes linearly polarized light through polarizer I (5), then quasi-parallel light is formed through lens II (6), and the field of view is limited by diaphragm II (7). The quasi-parallel light passes through the lens III (8), focuses and transmits the polarization-maintaining beamsplitter prism (10) to the front focal plane of the infinity system microscopic objective lens (11), and forms a beam of fine beams after the infinity system microscopic objective lens (11) to focus on On the sample (35), it is amplified by the infinity system microscope objective lens (11) after being reflected by the sample, and then reflected by the polarization maintaining beam splitter prism (10) to the filter II (13), and then passed through the electronically controlled roller type switching seat ( 46) Perform optional narrow-band filtering, then use the 1/4 wave plate (14) to improve the contrast of the imaging pattern of the magnetic domain structure, analyze the polarization by the analyzer (15), and finally use the tube lens (16) to image the magnetic domain to the CMOS camera (17). Through the magnetic domain image processing system of the present invention, the magnetic domain structure image on the surface of the ferromagnetic film as shown in Figure 4 can be observed, and the magnetic domain reversal process on the ferromagnetic film as shown in Figure 5 can also be observed with the change of the external magnetic field.

The optical fiber output end (2) can control the two-dimensional off-axis distance of the optical fiber beam through the electronically controlled two-dimensional translation stage I (37), so that the optical beam emitted by the optical fiber output end (2) is not on the main optical axis of the system, so as to achieve 35) to adjust the angle of the incident light for imaging (as shown in Figure 1, the dotted line issued from the output end of the optical fiber (2) indicates the change of the optical path after moving the light source, so that the angle of the incident light for imaging the sample can be adjusted), thereby adjusting the polarity of the magnetic domain imaging Axial Kerr and longitudinal Kerr signal components achieve the purpose of flexible switching between out-of-plane and in-plane magnetization component imaging.

Description of the optical path for local Kerr loop measurement: the laser light emitted by the laser (18) is attenuated by the attenuator I (19), then enters the aperture III (20), and then passes through the polarizer (21) to become linearly polarized light into the light Diaphragm IV (22), then through the telephoto concave lens (44) and the electric control roller switch seat (45) to fine-tune the spot size, the linearly polarized light is reflected by the dichroic mirror I (9) The objective lens (11) is focused on the sample (35), and is reflected after passing through the sample. The reflected light becomes elliptically polarized light due to the magneto-optic Kerr effect, enters the microscopic objective lens (11) of the infinity system, and then is reflected by the polarization-maintaining beamsplitter prism (10) and the dichroic mirror II (12), and the light is chopped in sequence device (23), attenuation plate II (24), aperture V (25), half-wave plate (26), optical filter (27), lens IV (28), aperture VI (29), through the Gran Prism (30) is decomposed into two bundles of light horizontally polarized light and vertically polarized light after, enters balance photodetector (32) respectively, and chopper (23) cooperates with lock-in amplifier (33) to measure Kerr signal, by computer ( 34) The data acquisition records the measurement data. After data processing, the hysteresis phenomenon observed on the ferromagnetic thin film as shown in Fig. 6 can be obtained.

The laser (18) can control the off-axis distance of the laser beam through the electronically controlled two-dimensional translation stage II (38), so that the light emitted by the laser (18) is not on the main optical axis of the system, so as to adjust the laser incident on the sample (35) The angle of the light (the dotted line emitted by the laser (18) in Figure 1 indicates the change of the optical path after moving the light source, so that the angle of the imaging incident light can be adjusted), and then adjust the polar Kerr sum measured by the local hysteresis loop The longitudinal Kerr signal component achieves the purpose of flexible switching between out-of-plane and in-plane magnetization component measurements. At the same time, in order to ensure that the balanced photodetector (32) can still receive light accurately after the laser is off-axis, an electronically controlled two-dimensional translation stage III (39) is added to the balanced photodetector (32) to compensate for off-axis movement .

When the laser moves to the left in the light emitting direction, the balance photodetector moves to the left in the light receiving direction correspondingly.

When the laser moves to the right in the light emitting direction, the balance photodetector moves to the right in the light receiving direction correspondingly.

When the laser moves toward the light-emitting direction, the balance photodetector moves correspondingly toward the light-receiving direction.

When the laser moves downward toward the light-emitting direction, the balance photodetector moves correspondingly toward the light-receiving direction.

The method can adjust the poloidal Kerr and longitudinal Kerr signal components of the local hysteresis loop.

The optical path of magneto-optical Kerr microscopic imaging and the optical path of local Kerr loop measurement pass through dichroic mirror Ⅰ (9), polarization maintaining beam splitter (10), infinity system microscopic objective lens (11) and dichroic Chromatic mirror II (12) connection, based on the wavelength selection of the dichroic mirror and the simple optical path design, realizes the coupling of two sets of optical path systems, the magneto-optic Kerr microscopic imaging optical path and the local Kerr loop measurement optical path, and then realizes the In the case of observing the magnetic domain structure, the local hysteresis loop can be accurately measured at the same time; in addition, the auxiliary visual selection of the measurement area of the local hysteresis loop based on the imaging of the magnetic domain structure of the sample can be realized.

The simultaneous operation of the magneto-optical Kerr microscopic imaging optical path and the local Kerr loop measurement optical path can accurately measure information such as local hysteresis loops to characterize the magnetic properties of magnetic materials while observing the magnetic domain structure.

The magneto-optical Kerr microscopic imaging optical path and the local Kerr loop measurement optical path are connected together through the dichroic mirror I (9) and the dichroic mirror II (12). The dichroic mirror I (9) and the dichroic mirror The reflection band of the dichroic mirror II (12) should contain the wavelength of the laser light source, while the transmission band should contain the wavelength of the fiber light source.

When the optical path of magneto-optical Kerr microscopic imaging and the optical path of local Kerr loop measurement work simultaneously, the sizes of the spots formed on the surface of magnetic material samples are different.

The typical diameter of the detection spot (that is, the magnetic domain imaging area) formed by the magneto-optical Kerr microscopic imaging optical path on the magnetic material is on the order of hundreds of microns. (By switching objective lenses with different magnifications, the spot size can be adjusted in the order of hundreds of microns according to requirements).

The typical diameter of the detection spot of the local Kerr loop measurement optical path in the magnetic material (that is, the detection area of the hysteresis loop) is on the order of microns to ten microns. The typical value of the focused spot of the laser beam after passing through the objective lens is on the order of microns. By adding telephoto concave lenses with different focal lengths in front of the objective lens, the laser beam diverges slightly after passing through the telephoto concave lens (44), and the diameter of the spot when it is focused on the sample is also It will be enlarged, so that the laser spot size can be adjusted between microns and ten microns according to requirements.

The size of the laser spot can be adjusted by selectively placing the above-mentioned telephoto concave lens (44) in the optical path system through the electronically controlled roller-type switching seat I (45), which can switch telephoto concave lenses with different focal lengths. After passing through telephoto concave lenses with different focal lengths, the light beam The degree of divergence is inconsistent, so that the spot size on the sample can be adjusted from microns to ten microns according to the needs, so as to meet the local testing needs of different scales. Because the divergence angle of the laser beam passing through the telephoto concave lens (44) is very small, its transmission in the optical path system is not affected.

The detection spot of the local Kerr loop measurement optical path is much smaller than the detection spot of the magneto-optical Kerr microscopic imaging optical path. The line measurement optical path can perform local point selection according to the imaged magnetic domain structure to measure the local hysteresis loop of the region of interest, and simultaneously measure the magnetic domain structure and local hysteresis loop for magnetic property research.

The method can accurately measure information such as local hysteresis loops to characterize the magnetic properties of magnetic materials under the condition of observing the magnetic domain structure.

The dichroic mirror II (12) has a lower transmittance to the laser light source band, but a higher reflectance. It has extremely high transmittance and extremely low reflectance for the light in the fiber optic light source band. Therefore, when the laser beam passes through the dichroic mirror II (12), a small part of the laser light can pass through the dichroic mirror II (12) to the CMOS camera (17) for imaging.

According to the selection of specific parameters of the dichroic mirror II (12), the magnetic domain structure can be observed in the optical path of magneto-optical Kerr microscopy imaging, and the CMOS camera (17) can be used to observe the local hysteresis loop measurement In the area of local hysteresis loop measurement, the local point selection function is performed by moving the sample, so that the measurement area of the magnetic material hysteresis loop can be visually selected, and the magnetic properties of the specific magnetic domain area can be studied.

The optical filter II (13) can filter out the light in the laser light source band in the local Kerr loop measurement optical path, and pass through the light in the optical fiber light source band to block the laser light source from imaging on the CMOS camera (17). The above-mentioned optical filter II (13) can be extracted and inserted into the optical path system through the electronically controlled roller type switching seat II (46).

The local point selection function of the local Kerr loop measurement optical path can be turned on or off through the electric control roller switch seat II (46) on the optical filter II (13). In Fig. 1, the laser passes through the optical filter II ( 13) is changed into a dotted line, which means that the function is optional. In the local hysteresis loop measurement, the point selection function can be turned on, and the magnetic domain area of interest can be selected to measure the hysteresis loop through magnetic domain imaging, while the point selection function can be turned off in the pure magnetic domain imaging detection to obtain a pure The magnetic domain structure imaging pattern.

Based on the selection of specific parameters of the dichroic mirror, before the measurement of the local hysteresis loop, the magnetic domain structure of the sample can be visually observed and the area for measuring the local hysteresis loop can be selected.

Electric control roller type switching seat I (45) and electric control roller type switching seat II (46) are a mirror frame for the Ferris wheel structure. There are 6 holes on the wheel that can be installed with 1.0 lenses. You only need to turn the wheel to switch different positions when using it. You can switch between telephoto concave lenses with different focal lengths in the optical path system, or pull out and insert filters in the optical path system. Tablet II (13).

Preferably, the sample and magnetic field control system includes a sample holder system and a magnetic field control system.

More preferably, the sample rack system includes a sample rack (40) and a sample (35), and the sample rack (40) includes a glass plate (42).

Wherein the sample (35) is placed on the sample holder (40), and the sample holder (40) is shown in Figure 2, and the linear Hall detector group (43) is placed inside the glass sheet (42) for detecting The magnitude of the three-dimensional magnetic field strength loaded on the sample (35) by the electromagnet group (36).

More preferably, the magnetic field control system includes an electromagnet group (36) and a linear Hall detector group (43).

A uniform three-dimensional magnetic field is applied to the sample (35) to change different magnetization vector components on the sample (35). The linear Hall detector group (43) can measure different magnetic field strengths loaded on the sample (35) by the electromagnet group (36) to give control feedback.

Preferably, the electronically controlled translation switching control system includes a translation switching system and a measurement optical measurement system.

More preferably, the measurement optical measurement system includes a CMOS camera (17) positioned on the left side of the tube lens (16), a balanced photodetector (32) placed in parallel below the Glan prism (30) and the mirror (31) And a lock-in amplifier (33) and a computer (34) for measurement.

More preferably, the translation switching system includes an electronically controlled two-dimensional translation stage I (37) for carrying and controlling the displacement of the optical fiber (1) and the optical fiber output end (2), an electronically controlled two-dimensional translation stage I (37) for carrying and controlling the displacement of the laser (18). Two-dimensional translation stage II (38), electronically controlled two-dimensional translation stage III (39) for carrying and controlling the displacement of the balanced photodetector (32), five-dimensional adjustment stage for carrying and controlling the displacement of the sample holder (40) (41), the electric control roller type switching seat I (45) for carrying and switching the telephoto concave lens (44), and the electric control roller type switching seat II (46) for carrying and switching the filter II (13) ).

Preferably, the dichroic mirror II (12) has a very high transmittance to the optical fiber light source band, while maintaining a low transmittance to the laser light source band, and is used to realize the imaging of the local magnetic field based on the magnetic domain structure of the sample. Auxiliary visual selection of the measurement area for the hysteresis line.

More preferably, the electronically controlled two-dimensional translation stage I (37) and the electronically controlled two-dimensional translation stage II (38) of the translation switching control system can control the position of the mounted light source according to the needs of use, and are used to change the incident light on the sample surface. In order to achieve the adjustment of the poloidal Kerr and longitudinal Kerr signal components measured by magnetic domain imaging and local hysteresis loops, the purpose of flexibly switching the measured magnetization vector components is achieved.

The CMOS camera (17) receives the output light from the optical path of magneto-optical Kerr microscopic imaging, and images the magnetic domain appearance. The balanced photodetector (32) receives the output light of the local Kerr loop measurement optical path, cooperates with the chopper (23) and the lock-in amplifier (33) to measure the Kerr signal, and records it through the data acquisition of the computer (34) Measurement data.

Among them, CMOS camera (17), lock-in amplifier (33), electromagnet group (36), electronically controlled two-dimensional translation stage I (37), electronically controlled two-dimensional translation stage II (38), and electronically controlled two-dimensional translation stage III (39), five-dimensional adjustment table (41), linear Hall detector group (43), electric control roller type switching seat I (45), electric control roller type switching seat II (46) are all connected with computer (34) , and can be controlled by a computer (34).

A balanced photodetector (32) and a chopper (23) are connected to a lock-in amplifier (33). The reflected light of the sample passes through the chopper (23), attenuation plate II (24), aperture V (25), half-wave plate (26), filter I (27), lens IV (28), aperture Ⅵ (29), decomposed into two beams of light horizontally polarized light and vertically polarized light by the Glan prism (30), these two beams of polarized light enter the balance photodetector (32) respectively to obtain two signals I1 and I2, in a small Under the angle approximation, the Kerr rotation angle variation △θk can be expressed as:

The method has high detection sensitivity, can greatly suppress the influence of noise, and increase the signal-to-noise ratio of the detection result.

The invention also designs a digital image processing algorithm, which effectively improves the contrast of the magnetic domain structure imaging pattern. Through the magnetization saturation difference technology, the magnetically dependent grayscale change image is obtained; the contrast is enhanced by grayscale transformation through histogram equalization and histogram normalization; the smoothing filter is performed through Gaussian filtering and bilateral filtering to eliminate noise; through Ostu threshold segmentation and The adaptive threshold segmentation algorithm realizes the separation of magnetic domains and saturated magnetic domains; for the problem of insufficient resolution, the super-resolution restoration method is used to obtain high-resolution image reconstruction.

The software of the present invention is as shown in Fig. 3 a flow chart of a processing program for magnetic domain image optimization, and the application program is divided into three major functional modules according to different functions: 1, image enhancement module; 2, smooth noise reduction module; 3, image segmentation module. After the application program is running, various controls will be loaded on the graphical interface. After loading the original magnetic domain picture, by selecting the image processing function, the corresponding button control is connected to the image processing slot function. The original image and the processed image are displayed separately.

The image enhancement module includes two sub-modules, histogram normalization and histogram equalization. Histogram normalization can preserve the gray-scale linear relationship of the original magnetic domain image, while histogram equalization can reveal more magnetic domain details and provide higher contrast of magnetic domain structure imaging patterns.

The smooth noise reduction module includes two sub-modules of Gaussian filtering and bilateral filtering. Gaussian filtering, as the basic smoothing noise reduction algorithm, can effectively eliminate noise and smooth the gray level changes of domain walls. For band-type magnetic domains with clear edges, the use of bilateral filtering can well ensure the sharpness of the edges.

The image segmentation module includes Ostu threshold segmentation and adaptive threshold segmentation. Ostu threshold segmentation is based on the image gray distribution consisting of two domain types with different magnetization, which is more consistent with magnetic domain imaging in principle. Adaptive threshold segmentation is based on the change trend of edge gray level, which can present more edge details, and does not deal with the gray level change of non-magnetic domains.

The software method improves the contrast of the imaging pattern of the magnetic domain structure and realizes super-resolution restoration.

Explain the present invention with an embodiment method step below:

Step 1: stick the sample on the glass thin plate (40) and place it under the microscope objective lens (11) of the infinity system, and measure the external magnetic field loaded on the sample (35) through the linear Hall detector group (43).

Step 2: Control the electronically controlled two-dimensional translation stage I (37), adjust the optical fiber output end (2) to the main optical axis of the optical system, adjust the analyzer (15) to a high-pass light angle, and use a CMOS camera (17) Take pictures, control the five-dimensional adjustment table (41) to adjust the height of the sample holder (40), so that the surface of the sample (35) coincides with the focal plane of the infinitely conjugated long working distance microscope objective lens (11), at this time the CMOS camera (17) Imaging is clear. At the same time, observe whether there is partial defocus in the picture, and control the five-dimensional adjustment table (41) to adjust the pitch of the sample holder (40), so that the surface of the sample (35) is perpendicular to the illumination beam, and the imaging picture is completely clear.

Step 3: adjust the polarizer (15) polarizer angle, increase the CMOS camera (17) exposure time and gain at the same time, keep the field of vision clear, when the polarizer (15) makes the imaging the darkest, then offset 5-10 ° .

Step 4: Control the electromagnet (36) to change the size of the applied magnetic field of the sample (35). For the first time, the external magnetic field is increased much more than the coercive force of the ferromagnetic sample, so that the sample (35) is completely saturated and magnetized.

Step 5: After the sample (35) is fully saturated and magnetized, reverse the applied magnetic field to provide a reverse magnetic field, and gradually increase the magnetic field from 0 to gradually reverse the magnetization of the sample (35). When the external magnetic field is applied to the multi-domain state, the magnetic domains appear and stop increasing the magnetic field. At this time, a 1/4 wave plate (14) is placed in the optical path, and the optical axis of the wave plate is rotated to maximize the contrast of the imaging pattern of the magnetic domain structure. The sample (35) is saturated and magnetized again, and the magnetization saturation image is collected, and the optical path preparation for magneto-optic Kerr microscopic imaging is completed.

Step 6: Reverse the external magnetic field again. During the process of gradually increasing the magnetic field from 0, a magnetic domain pattern will appear. Continuously reversing the external magnetic field can repeatedly collect the magnetic domain pattern, and the collected magnetic domain image can be processed by software .

Step 7: Turn on the laser (18), control the electronically controlled two-dimensional translation stage I (37) to adjust the laser (18) to the main optical axis of the optical path system, and balance the photodetector (32) and the chopper (23) At the same time, it is connected with the lock-in amplifier (33), and the chopper (23) is placed in the optical path. Adjust the lock-in amplifier (33) to an appropriate range position, turn the half-wave plate (26), so that the differential signal of the lock-in amplifier (33) is as close to zero as possible, and the preparation of the local Kerr loop measurement optical path is completed.

Step 8: Control the electronically controlled roller switch seat (46) to pull the filter II (13) out of the optical path, so that the laser spot can be imaged and observed in the CMOS camera (17), and the area to be measured is selected.

Step 9: Optionally, according to the local test requirements of different scales during the measurement of the local hysteresis loop, the electric control roller switch seat (46) can be controlled to selectively add telephoto lenses (44) with different focal lengths to Adjust the focused spot diameter of the laser beam on the sample, so that the spot size can be adjusted from microns to ten microns according to requirements, so as to measure hysteresis loops of different local scales.

Step 10: Simultaneously measure the magnetic domain imaging and the local hysteresis loop through the measurement control software, or measure the two separately.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand , the technical solution of the present invention may be modified or equivalently replaced without departing from the spirit and scope of the technical solution of the present invention.

Claims (9)

1. A dynamic magnetic domain imaging and local hysteresis loop synchronous measurement system, characterized in that it includes a magneto-optical Kerr microscopic imaging optical path, a local Kerr loop measurement optical path, a sample and magnetic field control system and an electronic control system Translation switching control system; The magneto-optical Kerr microscopic imaging optical path includes an optical fiber (1), an optical fiber output end (2), a lens I (3), a diaphragm I (4), and a polarizer I placed sequentially and horizontally on the same horizontal line (5), lens II (6), diaphragm II (7), lens III (8), polarization maintaining beam splitter (10) and infinity system microscopic objective lens (11), the magneto-optic Kerr microscopic imaging The optical path also includes an optical filter II (13), a 1/4 wave plate (14), an analyzer (15) and a tube lens (16) placed in sequence on the right left of the polarization maintaining beam splitter (10); The local Kerr loop measurement optical path includes a laser (18), an attenuation plate I (19), a diaphragm III (20), a polarizer II ( 21), stop IV (22), telephoto concave lens (44), dichroic mirror I (9) and dichroic mirror II (12), said dichroic mirror I (9) is located in lens III (8 ) and the polarization maintaining beam splitter (10), the dichroic mirror II (12) is located between the polarization maintaining beam splitter (10) and the filter II (13), the local Kerr loop The measurement optical path also includes a chopper (23), an attenuation plate II (24), a diaphragm V (25), a half-wave plate (26), a filter I (27), a lens IV (28), Diaphragm VI (29), Glan prism (30), reflection mirror (31). 2 . A dynamic magnetic domain imaging and local hysteresis loop synchronous measurement system according to claim 1 , wherein the sample and magnetic field control system includes a sample holder system and a magnetic field control system. 3 . 3. A kind of dynamic magnetic domain imaging and local hysteresis loop synchronous measurement system according to claim 2, is characterized in that, described sample holder system comprises sample holder (40) and sample (35), and described sample The shelf (40) includes a glass plate (42). 4. a kind of dynamic magnetic domain imaging and local hysteresis loop synchronous measurement system according to claim 2, is characterized in that, described magnetic field control system comprises electromagnet group (36) and linear Hall detector group ( 43). 5 . The dynamic magnetic domain imaging and local hysteresis loop synchronous measurement system according to claim 1 , wherein the electronically controlled translation switching control system includes a translation switching system and a measurement optical measurement system. 6. A kind of dynamic magnetic domain imaging and local hysteresis loop synchronous measurement system according to claim 5, is characterized in that, described measurement optics measurement system comprises the CMOS camera (17) that is positioned at tube lens (16) left side ), a balanced photodetector (32) placed in parallel below the Glan prism (30) and mirror (31), and a lock-in amplifier (33) and computer (34) for measurement. 7. A dynamic magnetic domain imaging and local hysteresis loop synchronous measurement system according to claim 6, characterized in that the translation switching system includes a device for carrying and controlling the optical fiber (1) and the optical fiber output end (2) An electronically controlled two-dimensional translation stage I (37) for displacement, an electronically controlled two-dimensional translation stage II (38) for carrying and controlling the displacement of the laser (18), an electronically controlled two-dimensional translation stage II (38) for carrying and controlling the displacement of the balanced photodetector (32) Two-dimensional translation stage III (39), five-dimensional adjustment stage (41) for carrying and controlling the displacement of the sample holder (40), electric control roller switch seat I for carrying and switching the telephoto concave lens (44) ( 45), and the electric control roller type switching seat II (46) for carrying and switching the filter II (13). 8. A kind of dynamic magnetic domain imaging and local hysteresis loop synchronous measurement system according to claim 1, is characterized in that, described dichroic mirror II (12) has extremely high transmittance to the optical fiber light source band , while maintaining a low transmittance for the laser light source band, it is used to realize the auxiliary visual selection of the measurement area of the local hysteresis loop based on the imaging of the magnetic domain structure of the sample. 9. A kind of dynamic magnetic domain imaging and local hysteresis loop synchronous measurement system according to claim 7, is characterized in that, the electronically controlled two-dimensional translation platform 1 (37) and the electronically controlled The two-dimensional translation stage II (38) can control the position of the mounted light source according to the needs of use, and is used to change the angle of the incident light on the sample surface, thereby realizing the adjustment of the polar Kerr sum measured by the magnetic domain imaging and the local hysteresis loop. The longitudinal Kerr signal component achieves the purpose of flexibly switching the measured magnetization vector component.

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