A dynamic magnetic domain imaging and local hysteresis loop synchronous measurement system

Abstract

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

Description

Technical Field

[0001] The present invention relates to the field of magnetism, and particularly to a system for synchronously measuring dynamic magnetic domain imaging and local hysteresis loop. Background Art

[0002] After the magnetic domain theory was proposed, magnetism developed rapidly. According to previous actual experiments and the proposed theoretical models, magnetic phenomena such as magnetization intensity, magnetization curve, and magnetostriction can be explained using the magnetic domain theory. Therefore, studying the shape of the magnetic domain structure of ferromagnetic materials and its variation trend with an external magnetic field is very important for improving the magnetic properties of magnetic materials.

[0003] Magnetic domain hypothesis: On a microscopic scale, ferromagnetic materials can be divided into many continuous and adjacent small regions according to the direction of atomic magnetic moments. In the demagnetized state of the whole material, the directions of atomic magnetic moments in each small region are random. Therefore, after the magnetic moments of each small region are cancelled each other out, the overall magnetic moment of the material is zero, so the whole material does not show magnetism externally. Each small region divided according to different orientations of atomic magnetic moments is called a magnetic domain.

[0004] Magnetic domains are components of the microscopic structure of magnetic materials, which link 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.

[0005] Magnetic domain imaging provides an intuitive way to explore the local magnetism and domain wall dynamics of ferromagnetic materials. The magnetic domain imaging technique using the magneto-optical Kerr effect - magneto-optical Kerr microscopy can non-destructively and effectively observe the magnetic domain structure.

[0006] However, at present, in the field of magnetism, in order to measure the magnetic domain structure and local hysteresis loop of different magnetization vectors, it is necessary to change the relative positions of the sample, detection device, light source, and microscope and perform measurements for each different magnetization vector separately, and the process is extremely cumbersome. In addition, it is difficult for the existing technology to accurately measure information such as local hysteresis loop while obtaining the magnetic domain structure image. To solve these problems, a system for synchronously measuring dynamic magnetic domain imaging and local hysteresis loop and an image processing method are proposed. Summary of the Invention

[0007] The present invention overcomes the deficiencies of the prior art and makes the following improvements and optimizations for the above-mentioned drawbacks.

[0008] The object of the present invention is achieved through the following technical solutions:

[0009] A system for synchronously measuring dynamic magnetic domain imaging and local hysteresis loop is provided, including a magneto-optical Kerr microscopy imaging optical path, a local Kerr loop measurement optical path, a sample and magnetic field control system, and an electric control translation and switching control system;

[0010] The magneto-optical Kerr microscopy imaging optical path includes an optical fiber (1), an optical fiber output end (2), a lens I (3), a diaphragm I (4), a polarizer I (5), a lens II (6), a diaphragm II (7), a lens III (8), a polarization-maintaining beam splitter (10), and an infinity system microscope objective (11) that are placed in sequence and horizontally on the same horizontal line. The magneto-optical Kerr microscopy imaging optical path further includes a filter II (13), a quarter-wave plate (14), an analyzer (15), and a tube lens (16) that are placed in sequence directly to the left of the polarization-maintaining beam splitter (10);

[0011] The local Kerr loop measurement optical path includes a laser (18), an attenuation sheet I (19), a diaphragm III (20), a polarizer II (21), a diaphragm IV (22), a long-focus concave lens (44), a dichroic mirror I (9), and a dichroic mirror II (12) that are placed perpendicular to the magneto-optical Kerr microscopy imaging optical path. The dichroic mirror I (9) is located between the lens III (8) and the polarization-maintaining beam splitter (10), and the dichroic mirror II (12) is located between the polarization-maintaining beam splitter (10) and the filter II (13). The local Kerr loop measurement optical path further includes a chopper (23), an attenuation sheet II (24), a diaphragm V (25), a half-wave plate (26), a filter I (27), a lens IV (28), a diaphragm VI (29), a Glan prism (30), and a mirror (31) that are placed in parallel in sequence.

[0012] Preferably, the sample and magnetic field control system includes a sample holder system and a magnetic field control system.

[0013] More preferably, the sample holder system includes a sample holder (40) and a sample (35), and the sample holder (40) includes a glass plate (42).

[0014] More preferably, the magnetic field control system includes an electromagnet group (36) and a linear Hall detector group (43).

[0015] Preferably, the electric control translation and switching control system includes a translation and switching system and a measurement optical measurement system.

[0016] More preferably, the measurement optical measurement system includes a CMOS camera (17) located to the left 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.

[0017] Preferably, the translation and switching system includes an electrically 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 electrically controlled two-dimensional translation stage II (38) for carrying and controlling the displacement of the laser (18), an electrically controlled two-dimensional translation stage III (39) for carrying and controlling the displacement of the balanced photodetector (32), a five-dimensional adjustment stage (41) for carrying and controlling the displacement of the sample holder (40), an electrically controlled roller-type switching seat I (45) for carrying and switching the long-focus concave lens (44), and an electrically controlled roller-type switching seat II (46) for carrying and switching the filter II (13).

[0018] Preferably, the dichroic mirror II (12) has an extremely high transmittance for the optical fiber light source band and a relatively low transmittance for the laser light source band, and is used to realize the auxiliary visual selection of the measurement area of the local hysteresis loop for the imaging of the sample magnetic domain structure.

[0019] Preferably, the electrically controlled two-dimensional translation stage I (37) and the electrically controlled two-dimensional translation stage II (38) of the translation and switching control system can control the position of the carried light source according to the usage requirements, so as to change the angle of the incident light on the sample surface, and further 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 the purpose of flexibly switching the measured magnetization vector components.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] 1. It can flexibly adjust the imaging and the angle of the incident light for measurement, and then simply 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 the purpose of flexibly switching the measured magnetization vector components. It can solve the complexity of changing the optical path when switching the polar Kerr and longitudinal Kerr signal components during the magnetic domain imaging and the local hysteresis loop measurement.

[0022] 2. It can simultaneously measure the magnetic domain structure imaging pattern and the local hysteresis loop information, and realize the characterization of the local magnetic domain structure and the magnetic hysteresis Kerr loop signal of the magnetic material based on the dual light sources. It solves the problem that the magnetic domain structure imaging pattern and the local hysteresis loop cannot be measured simultaneously.

[0023] 3. Before the local hysteresis loop measurement, based on the selection of specific parameters of the dichroic mirror, it can realize the visual observation of the sample magnetic domain structure to select the measurement area of the local hysteresis loop, and the size of the measurement area can be flexibly adjusted by switching the lens with a rotating wheel. It solves the problems that the local hysteresis loop cannot be visually selected and the size of the measurement area is difficult to adjust.

[0024] 4. The present invention uses a method for measuring the Kerr rotation angle by applying an optical balance bridge and a phase-locked amplification technique. This method has a high detection sensitivity, can greatly suppress the influence of noise, and increase the signal-to-noise ratio of the detection result. It improves the signal-to-noise ratio of the local loop Kerr signal and enhances the measurement accuracy.

[0025] 5. The present invention proposes a computer processing method for optimizing the imaging pattern of magnetic domains. This method improves the contrast of the magnetic domain structure imaging pattern and realizes super-resolution restoration. It improves the contrast of the magnetic domain imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be further described with reference to the accompanying drawings. However, the embodiments in the drawings do not constitute any limitation to the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the following drawings.

[0027] Figure 1 It is a schematic diagram of a dynamic magnetic domain imaging and local hysteresis loop synchronous measurement system provided by the present invention;

[0028] Figure 2 It is a schematic diagram of a magnetic thin film sample holder provided by the present invention;

[0029] Figure 3 It is a flowchart of a processing program for optimizing the magnetic domain image provided by the present invention;

[0030] Figure 4 It is a magnetic domain structure image collected on the surface of an FePt thin film by the present invention;

[0031] Figure 5 It is the magnetic domain reversal process observed on an FePt thin film by the present invention;

[0032] Figure 6 It is a local hysteresis loop measured on an FePt thin film by the present invention;

[0033] Reference numerals in the figure: 1, optical fiber; 2, optical fiber output end; 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; 12, dichroic mirror II; 13, filter II; 14, quarter-wave plate; 15, analyzer; 16, tube lens; 17, CMOS camera; 18, laser; 19, attenuation sheet I; 20, aperture III; 21, polarizer II; 22, aperture IV; 23, chopper; 24, attenuation sheet 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 stage; 42, glass plate; 43, linear Hall detector group; 44, long-focus concave lens; 45, electronically controlled roller-type switching seat I; 46, electronically controlled roller-type switching seat II. Detailed implementation manners

[0034] The following further describes in detail a dynamic magnetic domain imaging and local hysteresis loop synchronous measurement system in conjunction with specific embodiments. These embodiments are only for purposes of comparison and explanation, and the present invention is not limited to these embodiments.

[0035] 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. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0036] As Figure 1 shown, it includes a magneto-optical Kerr microscopy imaging optical path, a local Kerr loop measurement optical path, a sample and magnetic field control system, and an electronically controlled translation and switching control system;

[0037] The magneto-optical Kerr microscopy imaging optical path includes an optical fiber (1), an optical fiber output end (2), a lens I (3), an aperture I (4), a polarizer I (5), a lens II (6), an aperture II (7), a lens III (8), a polarization-maintaining beam splitter (10), and an infinity system microscope objective (11) that are sequentially placed and horizontally placed on the same horizontal line. The magneto-optical Kerr microscopy imaging optical path further includes a filter II (13), a quarter-wave plate (14), an analyzer (15), and a tube lens (16) that are sequentially placed directly to the left of the polarization-maintaining beam splitter (10);

[0038] The local Kerr loop measurement optical path includes a laser (18), an attenuation sheet I (19), a diaphragm III (20), a polarizer II (21), a diaphragm IV (22), a long focal length concave lens (44), a dichroic mirror I (9), and a dichroic mirror II (12) that are sequentially placed perpendicular to the magneto-optical Kerr microscopy imaging optical path. The dichroic mirror I (9) is located between the lens III (8) and the polarization-maintaining beam splitter (10), and the dichroic mirror II (12) is located between the polarization-maintaining beam splitter (10) and the filter II (13). The local Kerr loop measurement optical path further includes a chopper (23), an attenuation sheet II (24), a diaphragm V (25), a half-wave plate (26), a filter I (27), a lens IV (28), a diaphragm VI (29), a Glan prism (30), and a mirror (31) that are sequentially placed in parallel.

[0039] Among them, the chopper (23) performs chopping modulation on the light entering the balanced photodetector (32). In this embodiment, the chopper (23) is placed directly below the dichroic mirror II (12).

[0040] Explanation of the magneto-optical Kerr microscopy imaging optical path: Monochromatic light is transmitted through the optical fiber (1) to the optical fiber output end (2) and exits with a low divergence angle. Then it passes through the lens I (3) and is focused onto the diaphragm I (4) to filter out stray light and limit the aperture. Then it passes through the polarizer I (5) to become linearly polarized light, and then forms a quasi-parallel light beam through the lens II (6) and is limited in field of view by the diaphragm II (7). The quasi-parallel light passes through the lens III (8), is focused and transmitted through the polarization-maintaining beam splitter prism (10) to the front focal plane of the infinity system microscope objective (11). A thin light beam is formed behind the infinity system microscope objective (11) and is focused on the sample (35). After being reflected by the sample, it is magnified by the infinity system microscope objective (11) again, and then is reflected by the polarization-maintaining beam splitter prism (10) to the filter II (13). Optional narrowband filtering is performed through the electric control roller type switching seat (46). Then the 1 / 4 wave plate (14) is used to improve the contrast of the magnetic domain structure imaging pattern, the analyzer (15) is used for polarization analysis, and finally the tube lens (16) images the magnetic domain into 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 thin film can be observed, and as the external magnetic field changes, the magnetic domain inversion process on the ferromagnetic thin film can also be observed. Figure 4 The magnetic domain structure image on the surface of the ferromagnetic thin film, and as the external magnetic field changes, the magnetic domain inversion process on the ferromagnetic thin film can also be observed. Figure 5 The magnetic domain inversion process on the ferromagnetic thin film.

[0041] The optical fiber output end (2) can control the two-dimensional off-axis distance of the optical fiber beam through the electric control two-dimensional translation stage I (37), so that the light beam emitted from the optical fiber output end (2) is not on the main optical axis of the system, so as to adjust the angle of the imaging incident light at the sample (35) (such as Figure 1The dotted line emitted from the output end of the medium optical fiber (2) indicates the change in the optical path after moving the light source, enabling the adjustment of the angle of the incident light for sample imaging), and further adjusting the polar Kerr and longitudinal Kerr signal components of the magnetic domain imaging, achieving the purpose of flexibly switching between out-of-plane and in-plane magnetization component imaging.

[0042] Explanation of the optical path for local Kerr loop measurement: The laser emitted by the laser (18) passes through the attenuation sheet I (19) for attenuation and then enters the aperture III (20). It then passes through the polarizer (21) to become linearly polarized light and enters the aperture IV (22). After that, it undergoes fine adjustment of the spot size through the long focal length concave lens (44) and the electronically controlled roller type switching seat (45). The linearly polarized light is reflected by the dichroic mirror I (9) and focused on the sample (35) by the infinity system microscope objective (11). After passing through the sample, it is reflected. The reflected light becomes elliptically polarized light due to the magneto-optical Kerr effect and enters the infinity system microscope objective (11). Then it is reflected by the polarization-maintaining beam splitter prism (10) and the dichroic mirror II (12). The light sequentially passes through the chopper (23), attenuation sheet II (24), aperture V (25), half-wave plate (26), filter (27), lens IV (28), aperture VI (29), and after passing through the Glan prism (30), it is decomposed into two beams of light, horizontally polarized light and vertically polarized light, which respectively enter the balanced photodetector (32). The chopper (23) and the lock-in amplifier (33) cooperate to measure the Kerr signal, and the measurement data is recorded through data acquisition by the computer (34). After data processing, the magnetic hysteresis phenomenon observed on the ferromagnetic thin film can be obtained as Figure 6 the magnetic hysteresis phenomenon observed on the ferromagnetic thin film.

[0043] 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, in order to adjust the angle of the incident laser light at the sample (35) (such as Figure 1 The dotted line emitted by the laser (18) in the figure indicates the change in the optical path after moving the light source, enabling the adjustment of the angle of the incident light for imaging), and further adjusting the polar Kerr and longitudinal Kerr signal components of the local magnetic hysteresis loop measurement, achieving the purpose of flexibly 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 accurately receive light after the laser is off-axis, an electronically controlled two-dimensional translation stage III (39) is added to the balanced photodetector (32) to make corresponding compensatory off-axis movements.

[0044] When the laser moves left in the light-emitting direction, the balanced photodetector moves left in the light-receiving direction accordingly.

[0045] When the laser moves right in the light-emitting direction, the balanced photodetector moves right in the light-receiving direction accordingly.

[0046] When the laser moves up in the light-emitting direction, the balanced photodetector moves down in the light-receiving direction accordingly.

[0047] When the laser moves downward in the light-emitting direction, the balanced photodetector correspondingly moves upward in the light-receiving direction.

[0048] This method can adjust the polar Kerr and longitudinal Kerr signal components of the local hysteresis loop.

[0049] The magneto-optical Kerr microscopy optical path and the local Kerr loop measurement optical path are connected by a dichroic mirror I (9), a polarization-maintaining beam splitter (10), an infinity system microscope objective (11) and a dichroic mirror II (12). Based on the wavelength selection of the dichroic mirror and the concise optical path design, the coupling of the magneto-optical Kerr microscopy optical path and the local Kerr loop measurement optical path is realized, and then the local hysteresis loop can be accurately measured simultaneously while observing the magnetic domain structure; in addition, the measurement area of the local hysteresis loop can be visually selected assistively based on the imaging of the sample magnetic domain structure.

[0050] When the magneto-optical Kerr microscopy optical path and the local Kerr loop measurement optical path work simultaneously, it can accurately measure information such as the local hysteresis loop while observing the magnetic domain structure to characterize the magnetic properties of magnetic materials.

[0051] The magneto-optical Kerr microscopy optical path and the local Kerr loop measurement optical path are associated through dichroic mirror I (9) and dichroic mirror II (12). The reflection bands of the above-mentioned dichroic mirror I (9) and dichroic mirror II (12) should include the wavelength of the laser light source, and the transmission band includes the wavelength of the fiber light source.

[0052] When the magneto-optical Kerr microscopy optical path and the local Kerr loop measurement optical path work simultaneously, the spot sizes formed on the surface of the magnetic material sample are different.

[0053] The diameter of the detection spot (i.e., the magnetic domain imaging area) formed by the magneto-optical Kerr microscopy optical path on the magnetic material is typically on the order of hundreds of micrometers. (By switching objectives with different magnifications, the spot size can be adjusted within the order of hundreds of micrometers according to requirements).

[0054] The diameter of the detection spot (i.e., the hysteresis loop detection area) of the local Kerr loop measurement optical path on the magnetic material is typically on the order of micrometers to tens of micrometers. The typical value of the focused spot of the laser beam after passing through the objective is on the order of micrometers. By adding long-focus concave lenses with different focal lengths in front of the objective, the laser beam diverges slightly after passing through the long-focus concave lens (44), and the spot diameter when it is focused on the sample will also be enlarged, so that the laser spot size can be adjusted between the order of micrometers to tens of micrometers according to requirements.

[0055] The adjustment of the laser spot size can be achieved by selectively placing the above-mentioned long-focus concave lens (44) with different focal lengths in the optical path system through the electrically controlled roller-type switching base I (45). After passing through long-focus concave lenses with different focal lengths, the divergence degree of the light beam is inconsistent, enabling the spot size on the sample to be adjusted between the micrometer and ten-micrometer magnitude according to requirements to meet the local testing needs of different scales. Since the divergence angle of the laser beam passing through the long-focus concave lens (44) is very small, it does not affect its transmission in the optical path system.

[0056] The detection spot of the local Kerr loop measurement optical path is much smaller than that of the magneto-optical Kerr microscopy imaging optical path. Therefore, while observing the magnetic domain structure in the magneto-optical Kerr microscopy imaging optical path, the local Kerr loop measurement optical path can perform local point selection measurement on the local hysteresis loop of the region of interest according to the imaged magnetic domain structure, and study the magnetic properties by simultaneously measuring the magnetic domain structure and the local hysteresis loop.

[0057] This method can accurately measure information such as the local hysteresis loop while observing the magnetic domain structure, which is a method for characterizing the magnetic properties of magnetic materials.

[0058] The dichroic mirror II (12) has a low transmittance and a high reflectance for the laser light source band. It has an extremely high transmittance and an extremely low reflectance for the light in the fiber light source band. Therefore, when the laser passes through the dichroic mirror II (12), a small part of the laser can pass through the dichroic mirror II (12) to be imaged by the CMOS camera (17).

[0059] According to the selection of specific parameters of the dichroic mirror II (12), while observing the magnetic domain structure in the magneto-optical Kerr microscopy imaging optical path, the CMOS camera (17) can be used to observe the region of the local hysteresis loop measurement during the local hysteresis loop measurement. By moving the sample to perform the local point selection function, the measurement region of the magnetic hysteresis loop of the magnetic material can be visually selected to study the magnetic properties of a specific magnetic domain region.

[0060] The filter II (13) can filter out the light in the laser light source band in the local Kerr loop measurement optical path and pass the light in the fiber light source band to prevent the light of the laser light source from being imaged on the CMOS camera (17). The above filter II (13) can be withdrawn and inserted into the optical path system through the electrically controlled roller-type switching base II (46).

[0061] The local point selection function of the local Kerr loop measurement optical path can be turned on or off through the electrically controlled roller-type switching base II (46) on the filter II (13). Figure 1When the medium laser passes through the filter II (13) and becomes a dotted line, it indicates that this function is optional. In the measurement of local hysteresis loops, the point selection function can be enabled to assist in selecting the magnetic domain regions of interest for measuring hysteresis loops through magnetic domain imaging, while in the pure magnetic domain imaging detection, the point selection function can be disabled to obtain a pure magnetic domain structure imaging pattern.

[0062] Based on the selection of specific parameters of the dichroic mirror, it is possible to visually observe the magnetic domain structure of the sample before measuring the local hysteresis loop and select the region for measuring the local hysteresis loop.

[0063] The electronically controlled roller type switching seat I (45) and the electronically controlled roller type switching seat II (46) are a mirror frame in the shape of a Ferris wheel. There are 6 holes on the wheel disc for installing 1.0 lenses. During use, only by rotating the wheel can different positions be switched, so as to switch different focal length long focal concave lenses in the optical path system, or withdraw and insert the filter II (13) in the optical path system.

[0064] Preferably, the sample and magnetic field control system includes a sample holder system and a magnetic field control system.

[0065] More preferably, the sample holder system includes a sample holder (40) and a sample (35), and the sample holder (40) includes a glass plate (42).

[0066] Wherein the sample (35) is placed on the sample holder (40), and the sample holder (40) is as Figure 2 shown. The linear Hall detector group (43) is placed inside the thin glass plate (42) and is used to detect the magnitude of the three-dimensional magnetic field intensity applied by the electromagnet group (36) on the sample (35).

[0067] More preferably, the magnetic field control system includes an electromagnet group (36) and a linear Hall detector group (43).

[0068] 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 intensities applied by the electromagnet group (36) on the sample (35) to give control feedback.

[0069] Preferably, the electronically controlled translation switching control system includes a translation switching system and a measurement optical measurement system.

[0070] More preferably, the measurement optical measurement system includes a CMOS camera (17) located to the left of the tube lens (16), a balanced photodetector (32) placed in parallel below the Glan prism (30) and the mirror (31), as well as a lock-in amplifier (33) and a computer (34) for measurement.

[0071] Preferably, the translation and 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 II (38) for carrying and controlling the displacement of the laser (18), an electronically controlled two-dimensional translation stage III (39) for carrying and controlling the displacement of the balanced photodetector (32), a five-dimensional adjustment stage (41) for carrying and controlling the displacement of the sample holder (40), an electronically controlled roller-type switching seat I (45) for carrying and switching the long-focus concave lens (44), and an electronically controlled roller-type switching seat II (46) for carrying and switching the filter II (13).

[0072] Preferably, the dichroic mirror II (12) has an extremely high transmittance for the optical fiber light source band and a relatively low transmittance for the laser light source band, and is used to achieve an auxiliary visual selection of the measurement area of the local hysteresis loop based on the sample magnetic domain structure imaging.

[0073] Preferably, the electronically controlled two-dimensional translation stage I (37) and the electronically controlled two-dimensional translation stage II (38) of the translation and switching control system can control the position of the carried light source according to the usage requirements, so as to change the angle of the incident light on the sample surface, and further adjust the polar Kerr and longitudinal Kerr signal components measured by the magnetic domain imaging and the local hysteresis loop, so as to achieve the purpose of flexibly switching the measured magnetization vector components.

[0074] The CMOS camera (17) receives the output light of the magneto-optical Kerr microscopy imaging optical path 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 the measurement data through the data acquisition of the computer (34).

[0075] Among them, the CMOS camera (17), the lock-in amplifier (33), the electromagnet group (36), the electronically controlled two-dimensional translation stage I (37), the electronically controlled two-dimensional translation stage II (38), the electronically controlled two-dimensional translation stage III (39), the five-dimensional adjustment stage (41), the linear Hall detector group (43), the electronically controlled roller-type switching seat I (45), and the electronically controlled roller-type switching seat II (46) are all connected to the computer (34) and can be controlled by the computer (34).

[0076] The balanced photodetector (32) and the chopper (23) are connected to the lock-in amplifier (33). The reflected light of the sample sequentially passes through the chopper (23), the attenuation sheet II (24), the aperture V (25), the half-wave plate (26), the filter I (27), the lens IV (28), the aperture VI (29), and is decomposed into two beams of light, horizontally polarized light and vertically polarized light, by the Glan prism (30). These two beams of polarized light respectively enter the balanced photodetector (32) to obtain two signals I1 and I2. In the small-angle approximation, the change amount of the Kerr rotation angle △θk can be expressed as:

[0077]

[0078] This method has a high detection sensitivity, can greatly suppress the influence of noise, and increase the signal-to-noise ratio of the detection result.

[0079] The present 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, a magnetic field-dependent gray-scale change image is obtained; through histogram equalization and histogram normalization for gray-scale transformation to enhance the contrast; through Gaussian filtering and bilateral filtering for smoothing filtering to eliminate noise; through Otsu threshold segmentation and adaptive threshold segmentation algorithms, the separation of magnetic domains and saturated magnetic domains is realized; for the problem of insufficient resolution, the super-resolution restoration method is used to obtain high-resolution image reconstruction.

[0080] The software of the present invention, such as Figure 3 A flowchart of a processing program for optimizing magnetic domain images divides the application program into three major functional modules according to different functions: 1. Image enhancement module; 2. Smoothing and noise reduction module; 3. Image segmentation module. After the application program runs, 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 associated with the slot function of the image processing. The original image and the processed image are displayed respectively.

[0081] The image enhancement module includes two sub-modules: histogram normalization and histogram equalization. Histogram normalization can retain the gray-scale linear relationship of the original magnetic domain image, while histogram equalization can show more details of the magnetic domain and provide a higher contrast of the magnetic domain structure imaging pattern.

[0082] The smoothing and noise reduction module includes two sub-modules: Gaussian filtering and bilateral filtering. As a basic smoothing and noise reduction algorithm, Gaussian filtering can effectively eliminate noise and smooth the gray-scale change of the domain wall. For strip-shaped magnetic domains with clear edges, bilateral filtering can well ensure the clarity of the edges.

[0083] The image segmentation module includes Otsu threshold segmentation and adaptive threshold segmentation. Otsu threshold segmentation is based on the fact that the image gray-scale distribution consists of two types of domains with different magnetizations, and in principle, it is more in line with magnetic domain imaging. Adaptive threshold segmentation is based on the change trend of the edge gray-scale for segmentation, can present more edge details, and does not process the gray-scale change of non-magnetic domains.

[0084] This software method improves the contrast of the magnetic domain structure imaging pattern and realizes super-resolution restoration.

[0085] The following uses the method steps of an embodiment to explain the present invention:

[0086] Step 1: Stick the sample onto the glass sheet (40) and place it under the infinity system microscope objective (11). Measure the external magnetic field applied to the sample (35) through the linear Hall detector array (43).

[0087] Step 2: Control the electronically controlled two-dimensional translation stage I (37) to adjust the fiber optic output end (2) onto the principal optical axis of the optical path system. Adjust the polarizer (15) to the high light transmission angle. Use the CMOS camera (17) to take a picture. Control the five-dimensional adjustment stage (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 infinity conjugate long working distance microscope objective (11). At this time, the imaging of the CMOS camera (17) is clear. At the same time, observe whether there is partial defocus in the picture. Control the five-dimensional adjustment stage (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.

[0088] Step 3: Adjust the polarization angle of the polarizer (15). At the same time, increase the exposure time and gain of the CMOS camera (17) to keep the field of view clear. When the imaging is darkest with the polarizer (15), shift it by another 5 - 10°.

[0089] Step 4: Control the electromagnet (36) to change the magnitude of the external magnetic field applied to the sample (35). First, increase the external magnetic field far greater than the coercive force of the ferromagnetic sample to fully saturate the magnetization of the sample (35).

[0090] Step 5: After the sample (35) is fully saturated magnetized, reverse the external 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 and magnetic domains appear, stop increasing the magnetic field. At this time, place a quarter-wave plate (14) in the optical path and rotate the optical axis of the wave plate to make the contrast of the magnetic domain structure imaging pattern the highest. Saturate the magnetization of the sample (35) again and collect the magnetically saturated image. The preparatory work for the magneto-optical Kerr microscopy imaging optical path is completed.

[0091] Step 6: Reverse the external magnetic field again. During the process of gradually increasing the magnetic field from 0, magnetic domain patterns will appear. Continuously reversing the external magnetic field can repeatedly collect magnetic domain patterns, and the collected magnetic domain images can be processed by software.

[0092] Step 7: Turn on the laser (18). Control the electronically controlled two-dimensional translation stage I (37) to adjust the laser (18) onto the principal optical axis of the optical path system. Connect the balanced photodetector (32) and the chopper (23) to the lock-in amplifier (33) at the same time and place the chopper (23) in the optical path. Adjust the lock-in amplifier (33) to the appropriate range position and rotate the half-wave plate (26) to make the differential signal of the lock-in amplifier (33) as close to zero as possible. The preparatory work for the local Kerr loop measurement optical path is completed.

[0093] Step 8: Control the electrically controlled roller-type switching base (46) to withdraw the filter II (13) from the optical path, so that the laser spot can be imaged and observed in the CMOS camera (17), and select the area to be measured.

[0094] Step 9: Optionally, for local test requirements of different scales during the measurement of the local hysteresis loop, the electrically controlled roller-type switching base (46) can be controlled to selectively add telephoto lenses (44) with different focal lengths to adjust the diameter of the focused laser spot on the sample, so that the spot size can be adjusted between the micrometer and ten-micrometer levels according to requirements, in order to measure the hysteresis loops of different local scales.

[0095] Step 10: Synchronously measure the magnetic domain imaging and the local hysteresis loop through the measurement control software, or measure the two separately.

[0096] 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 that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A dynamic magnetic domain imaging and local hysteresis loop synchronous measurement system, characterized in that, It includes a magneto-optical Kerr microscopy optical path, a local Kerr loop measurement optical path, a sample and magnetic field control system, and an electronically controlled translation and switching control system; The magneto-optical Kerr microscopy optical path includes a fiber optic (1), a fiber optic output end (2), a lens I (3), a diaphragm I (4), a polarizer I (5), a lens II (6), a diaphragm II (7), a lens III (8), a polarization-maintaining beam splitter (10), and an infinity system microscope objective (11) that are placed in sequence and horizontally on the same horizontal line. The magneto-optical Kerr microscopy optical path also includes a filter II (13), a quarter-wave plate (14), an analyzer (15), and a tube lens (16) that are placed in sequence directly to the left of the polarization-maintaining beam splitter (10); The local Kerr loop measurement optical path includes a laser (18), an attenuation sheet I (19), a diaphragm III (20), a polarizer II (21), a diaphragm IV (22), a long-focus concave lens (44), a dichroic mirror I (9), and a dichroic mirror II (12) that are placed perpendicular to the magneto-optical Kerr microscopy optical path. The dichroic mirror I (9) is located between the lens III (8) and the polarization-maintaining beam splitter (10), and the dichroic mirror II (12) is located between the polarization-maintaining beam splitter (10) and the filter II (13). The local Kerr loop measurement optical path also includes a chopper (23), an attenuation sheet II (24), a diaphragm V (25), a half-wave plate (26), a filter I (27), a lens IV (28), a diaphragm VI (29), a Glan prism (30), and a mirror (31) that are placed in parallel in sequence; The electronically controlled translation and switching control system includes a translation and switching system and a measurement optical measurement system; The measurement optical measurement system includes a CMOS camera (17) located to the left 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; The translation and switching system includes an electronically controlled two-dimensional translation stage I (37) for carrying and controlling the displacement of the fiber optic (1) and the fiber optic output end (2), 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 III (39) for carrying and controlling the displacement of the balanced photodetector (32), a five-dimensional adjustment stage (41) for carrying and controlling the displacement of the sample holder (40), an electronically controlled roller-type switching seat I (45) for carrying and switching the long-focus concave lens (44), and an electronically controlled roller-type switching seat II (46) for carrying and switching the filter II (13).

2. The 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. The dynamic magnetic domain imaging and local hysteresis loop synchronous measurement system according to claim 2, wherein The sample holder system includes a sample holder (40) and a sample (35), and the sample holder (40) includes a glass plate (42).

4. A dynamic magnetic domain imaging and local hysteresis loop synchronous measurement system according to claim 2, characterized in that, The magnetic field control system includes an electromagnet group (36) and a linear Hall detector group (43).

5. A dynamic magnetic domain imaging and local hysteresis loop synchronous measurement system according to claim 1, characterized in that, The dichroic mirror II (12) has an extremely high transmittance for the fiber light source band and a relatively low transmittance for the laser light source band, and is used to visually select the measurement area of the local hysteresis loop for the sample magnetic domain structure imaging in an auxiliary manner.

6. The dynamic magnetic domain imaging and local hysteresis loop synchronous measurement system according to claim 1, wherein The electronically controlled two-dimensional translation stage I (37) and the electronically controlled two-dimensional translation stage II (38) of the electronically controlled translation and switching control system can control the position of the carried light source according to the usage requirements, and are used to change the angle of the incident light on the sample surface, so as to adjust the polar Kerr and longitudinal Kerr signal components measured by the magnetic domain imaging and the local hysteresis loop, and achieve the purpose of flexibly switching the measured magnetization vector components.

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