A magneto-optical kerr microscope and a method for obtaining magnetic domain wall images

Abstract

The application relates to a magneto-optical Kerr measurement device and a method for acquiring a magnetic domain wall image. The magneto-optical Kerr measurement device comprises a magneto-optical Kerr microscope, wherein the magneto-optical Kerr microscope comprises an ocular lens and a CMOS camera; and an event camera, wherein the event camera comprises an underlying chip, the event camera is arranged on the ocular lens of the magneto-optical Kerr microscope, and the event camera is in a confocal plane with the CMOS camera. The method is to acquire a magnetic domain wall image by using the event camera in the magneto-optical Kerr measurement device. The application can improve the rapid detection of the magnetic material, has high resolution, is simple to operate, and has important significance for the research and development of the magnetic material.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of microscopy, in particular to a magneto-optical Kerr microscope and a method for acquiring magnetic domain wall images. BACKGROUND

[0002] When a linearly polarized light is reflected by a magnetic medium, the polarization plane of the reflected light is deflected by a small angle (Kerr rotation angle) relative to the polarization plane of the incident light, which is called the magneto-optical Kerr effect. This effect combined with microscopy technology forms a magneto-optical Kerr microscope, which is widely used in magnetic measurement of magnetic materials and magnetic domain observation.

[0003] All current magneto-optical Kerr microscope devices use ordinary CMOS cameras, with an upper limit of 100 frames, i.e. only 100 images can be collected per second. Considering the data transmission process, the test is generally 60 frames. Although a high-speed camera can increase the upper limit to 1000 frames, the amount of data generated is too large to be transmitted to the computer in real time for real-time imaging, and can only be stored in a data card for later processing and imaging. SUMMARY

[0004] In view of the problems in the prior art, the present application provides a magneto-optical Kerr microscope and a method for acquiring magnetic domain wall images. The technical solutions of the present application are as follows:

[0005] A magneto-optical Kerr measuring device, comprising:

[0006] A magneto-optical Kerr microscope, the magneto-optical Kerr microscope comprising an eyepiece and a CMOS camera.

[0007] An event camera, the event camera comprising a bottom chip, the event camera being arranged on the eyepiece of the magneto-optical Kerr microscope, and the event camera and the CMOS camera being in a common focal plane.

[0008] As a preferred technical solution, the number of eyepieces is 1.

[0009] As a preferred technical solution, a magneto-optical Kerr imaging light path is included, the magneto-optical Kerr imaging light path comprising an incident light path and an imaging light path, and the reflected light of the imaging light path forming a magnetic domain wall image at the common focal plane.

[0010] As a preferred technical solution, the incident light path is used to provide linearly polarized light, the imaging light path is used to collect reflected light by a magnetic material, and the polarization information of the reflected light is processed by a polarizing device to form an image.

[0011] As a preferred technical solution, the event camera can output event information according to the dynamic change of the light intensity of the imaging light path.

[0012] Preferably, the bottom chip comprises an amplification circuit, a difference circuit and a comparison circuit, and the event information is output after the light intensity dynamic change signal of the imaging light path is processed by the bottom chip.

[0013] Preferably, the event information comprises a motion path of the magnetic domain in space and time.

[0014] Preferably, the event camera can move in the vertical direction and record the motion process of the magnetic domain.

[0015] Preferably, the speed of the event camera in collecting the event information is 200 frames / s.

[0016] Preferably, the magneto-optical Kerr microscope further comprises an LED light source, a beam splitter, a sample holder, an electromagnet, a polarizer and an analyzer.

[0017] The application further provides a method for obtaining a magnetic domain wall image, comprising:

[0018] The event camera is arranged on an ocular lens of the magneto-optical Kerr microscope, and the event camera and the CMOS camera are adjusted to be in a confocal plane.

[0019] The measured magnetic sample is fixed on the sample holder of the magneto-optical Kerr microscope.

[0020] A magnetic field is applied.

[0021] The light emitted by the light source passes through the polarizer, and linearly polarized light is irradiated on the surface of the measured magnetic sample. The light reflected from the surface of the measured sample passes through the analyzer, and the light intensity dynamic change after the analyzer is detected by the event camera, so as to obtain the magnetic domain wall image of the measured magnetic sample.

[0022] Preferably, the direction of the magnetic field is perpendicular to the surface of the measured magnetic sample.

[0023] Preferably, the method further comprises the following processing performed by the event camera:

[0024] The light intensity dynamic change detected by the event camera is converted into an electrical signal.

[0025] The electrical signal is processed by the difference circuit, and a change amount is obtained.

[0026] The change amount is transmitted to the comparison circuit, and the change amount is compared with a preset threshold.

[0027] When the change amount exceeds the preset threshold, the event information is output.

[0028] Preferably, the change amount is a change amount from the beginning of the previous event information to now.

[0029] The technical scheme adopted by the application has the following beneficial effects:

[0030] The application provides a magneto-optical Kerr microscope device, realizes high resolution and increases measurement precision, can accurately and efficiently obtain magnetic information of a magnetic material, and can detect samples of any size without affecting the magnetization state of the sample and with high time resolution.

[0031] The application provides a method for obtaining a magnetic domain wall image based on the magneto-optical Kerr microscope device, which is simple to operate and low in cost, greatly improves the observation of the magnetic information of the magnetic material, and provides more possibilities for magnetic research. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the application, the drawings needed to be used in the embodiment description will be briefly introduced as follows, which form a part of the application. The illustrative embodiments of the application and the description and explanation thereof do not constitute an improper limitation on the application. In the drawings:

[0033] Figure 1 The display module structure schematic diagram disclosed by the application embodiments 1-2 is shown in the figure;

[0034] Figure 2 The display module structure schematic diagram disclosed by the application embodiments 1-2 is shown in the figure;

[0035] Figure 3 The display module structure schematic diagram disclosed by the application embodiments 1-2 is shown in the figure;

[0036] Figure 4 The display module structure schematic diagram disclosed by the application embodiments 1-2 is shown in the figure;

[0037] Figure 5 The display module structure schematic diagram disclosed by the application embodiments 1-2 is shown in the figure.

[0038] Explanation of reference signs:

[0039] CMOS camera 10, LED light source 101, polarizer 102, analyzer 103, beam splitter 104, sample holder 105, electromagnet 106;

[0040] Event camera 20, sensing circuit 201, differential circuit 202, comparison circuit 203. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solutions and advantages of the application more clear, the technical solutions of the application will be described clearly and completely in combination with the specific embodiments of the application and the corresponding drawings. In the description of the application, it should be noted that the term "or" is generally used in the sense of including "and / or", unless the context clearly indicates otherwise.

[0042] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connecting" should be understood in a broad sense, for example, can be fixedly connected, can be detachably connected, or integrally connected; can be mechanically connected, can be electrically connected; can be directly connected, can be indirectly connected through an intermediate medium, or can be internal communication of two elements. For those skilled in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances.

[0043] Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0044] Example 1

[0045] The present embodiment provides a magneto-optical Kerr measurement device, according to Figure 1 , comprising:

[0046] A magneto-optical Kerr microscope, the magneto-optical Kerr microscope comprising an eyepiece, a CMOS camera 10;

[0047] An event camera 20, the event camera 20 comprising a bottom chip, the event camera 20 being disposed on the eyepiece of the magneto-optical Kerr microscope, and the event camera 20 being in a confocal plane with the CMOS camera 10.

[0048] The main principle of magneto-optical Kerr technology is that when a linearly polarized light is reflected by a magnetic material, the polarization plane of the reflected light will have a small angle deflection relative to the polarization plane of the incident light, which is called magneto-optical Kerr effect. When the reflected light passes through the analyzer 103, a pattern will be formed on the camera, which is the pattern of magnetic domains.

[0049] The event camera 20 acquires information by sensing the dynamic changes of the light intensity of the scene. The event camera 20 is an "asynchronous" triggered camera, and the output is the pixel coordinates, trigger time and polarity of the event points. Each event point is independently photosensitive and transmitted, and the event camera 20 has the advantages of high time resolution and low delay, high dynamic range and extremely low power consumption.

[0050] Preferably, the number of eyepieces is 1. The magneto-optical Kerr microscope further comprises an LED light source 101, a beam splitter 104, a sample holder 105, an electromagnet 106, a polarizer 102 and an analyzer 103. The LED (Light-Emitting Diode) light source, the LED light source 101 is a light-emitting diode light source, which can obtain very strong contrast and has a relatively long service life.

[0051] The event camera 20 is arranged on one of the eyepieces of the magneto-optical Kerr microscope, and the other eyepiece is shielded or removed, or is reserved according to the requirement. The event camera 20 is arranged at an angle of 45 degrees with the CMOS camera 10, so that the confocal plane can be better determined, so that the event camera 20 obtains an image at the confocal plane, and the CMOS camera 10 can be removed after the confocal plane is determined.

[0052] Preferably, the magneto-optical Kerr imaging light path comprises an incident light path and an imaging light path, and the reflected light of the imaging light path forms a domain wall image at the confocal plane.

[0053] Preferably, the incident light path is used to provide linearly polarized light, and the imaging light path is used to collect light reflected by the magnetic material, and the polarization information of the reflected light is processed by a polarizing detector to form an image.

[0054] According to Figure 1 , the light emitted by the LED light source 101 passes through the polarizer 102 and is converted into linearly polarized light, and is irradiated onto the sample. Due to the existence of magnetic domains in the sample, the magnetization intensity and direction in each region of the sample are different, so the change of the polarization plane of the linearly polarized light by different regions is different. Therefore, when the reflected light passes through the polarizing detector 103, the intensity distribution of the light spot is different, and the domain wall image of the sample can be obtained by detecting the event camera 20.

[0055] The magnetic domain image collected by the CMOS camera 10 of the magneto-optical Kerr microscope is shown in Figure 2 , and the two kinds of contrasts correspond to magnetic domains in different directions, and the boundary between the two kinds of contrasts is the domain wall. The domain wall image collected by the event camera 20 is shown in Figure 3 , only the moving domain wall can be seen, which is determined by the characteristics of the event camera 20. Only when the light intensity changes, the event camera 20 will record data, so only the change of the position of the domain wall is recorded.

[0056] Preferably, the event camera 20 can output event information according to the dynamic change of the light intensity of the imaging light path. According to the working principle of the event camera 20, when the brightness change of the corresponding pixel point reaches a certain threshold value, the event camera 20 will trigger an event. Such events are discrete and asynchronous points.

[0057] Preferably, the bottom chip comprises an amplifying circuit, a differential circuit 202 and a comparison circuit 203, and the event information is output after the dynamic change signal of the light intensity of the imaging light path is processed by the bottom chip.

[0058] The event camera 20 adopts a completely different structure from the traditional camera from the design of the bottom chip. According to Figure 4The event camera 20 includes a light-sensing circuit 201 to sense dynamic changes in light intensity. It also features a pre-amplifier circuit for photoelectric conversion. Each pixel in the event camera 20 incorporates a time-difference circuit 202 and a comparator circuit 203. An event signal is only output when the light intensity change signal output by the difference circuit 202 exceeds a threshold. Conversely, when the light intensity change is small or slow, the pixel does not generate a signal. The light intensity change signal is converted into event data by special circuits in the event camera 20. Each event includes the pixel coordinates, polarity (increase or decrease in light intensity), and a timestamp. The timestamp can achieve a very high time resolution; currently commercially available models can reach microseconds. The magneto-optical Kerr measurement device of this embodiment plays an important role in the dynamic and static observation of magnetic materials and magnetic thin film domains.

[0059] Preferably, the event information includes the spatial and temporal movement paths of the magnetic domains.

[0060] Preferably, the event camera 20 is capable of moving vertically and recording the magnetic domain motion process.

[0061] Preferably, the event camera 20 acquires event information at a rate of 200 frames / s.

[0062] Example 2

[0063] This embodiment provides a method for acquiring magnetic domain wall images based on Embodiment 1. Figure 5 ,include:

[0064] The event camera 20 is mounted on the eyepiece of the magneto-optical Kerr microscope, and the event camera 20 and the CMOS camera 10 are adjusted to be in the same focal plane.

[0065] The magnetic sample to be tested is fixed on the sample holder 105 of the magneto-optical Kerr microscope;

[0066] Applying a magnetic field drives the movement of the magnetic domain walls;

[0067] The light emitted from the light source, after passing through polarizer 102, becomes linearly polarized and illuminates the surface of the magnetic sample under test. The dynamic changes in light intensity reflected from the sample surface, after passing through analyzer 103, are detected by event camera 20, thus obtaining an image of the magnetic domain walls of the sample. Figure 2 .

[0068] according to Figure 1 The event camera 20 is placed on the eyepiece of the magneto-optical Kerr microscope and adjusted to be confocal with the COMS camera. In actual operation, the event camera 20 needs to be at a 45-degree angle to the COMS camera.

[0069] The measured magnetic sample (such as iron, cobalt, nickel and alloys thereof) is fixed on the sample support 105 by double-sided tape, and the sample holder is placed in the hole in the center of the magnet holder. After the measured magnetic sample is placed, the screw of the sample holder is tightened, so that the measured magnetic sample is fixed, and the position of the sample is prevented from changing slightly when a magnetic field is applied, which affects the measurement of the magneto-optical Kerr signal.

[0070] After the optical path is adjusted, a magnetic field is applied. Different strengths and directions of the magnetic field can be set according to requirements, or can be set by a person skilled in the art according to requirements, which are not specifically limited in the embodiment. Preferably, the direction of the magnetic field is perpendicular to the surface of the measured magnetic sample. Linearly polarized light is irradiated on the surface of the measured magnetic sample. According to the Faraday effect, the reflected light becomes circularly polarized light, and the polarization plane changes by an angle. The change in the polarization plane can be detected by the polarizer 103. The change in the light intensity passing through the polarizer 103 can correspond to the change in the magnetic domain of the magnetic material, and the change in the light intensity is detected by the event camera 20.

[0071] The event camera 20 does not measure the absolute light intensity, but measures the change in the light intensity. Figure 4 Each pixel of the event camera 20 has an analog circuit that performs the following logical functions:

[0072] The light sensor of the event camera 20 converts the dynamic change in the detected light intensity into an electrical signal;

[0073] The electrical signal is processed by the differential circuit 202 and the comparator, calculates the change (difference) from the last event to the present, and compares it with the preset internal threshold to determine whether to trigger an event;

[0074] When the change exceeds the preset threshold, an event is triggered, and the event camera 20 marks the event with a microsecond resolution and outputs an asynchronous event stream;

[0075] After the event is triggered, the differential circuit 202 is reset and starts calculating the difference of the next event.

[0076] The above describes an embodiment of the magneto-optical Kerr microscope and a method for obtaining a magnetic domain wall image. The principles and implementation modes of the present application are described by applying specific examples. The above description of the embodiments is only used to help understand the method and its core idea; meanwhile, for those skilled in the art, the specific implementation modes and application ranges can be changed according to the idea of the present application. In view of the above, the content of the specification should not be understood as a limitation of the present application.

Claims

1. A magneto-optical Kerr measuring device, characterized in that, include: A magneto-optical Kerr microscope, comprising an eyepiece and a CMOS camera; An event camera, comprising an underlying chip, is mounted on the eyepiece of the magneto-optical Kerr microscope and shares a common focal plane with the CMOS camera; the event camera has a light-sensing circuit for sensing dynamic changes in light intensity. The magneto-optical Kerr measurement device includes a magneto-optical Kerr imaging optical path, which includes an incident optical path and an imaging optical path. The reflected light from the imaging optical path forms a magnetic domain wall image at the confocal plane. The event camera can output event information based on the dynamic changes in light intensity of the imaging optical path; The event information includes the spatial and temporal movement paths of the magnetic domains.

2. The magneto-optical Kerr measuring device according to claim 1, characterized in that, The number of eyepieces is 1.

3. The magneto-optical Kerr measurement device according to claim 1, wherein the incident optical path is used to provide linearly polarized light, the imaging optical path is used to collect light reflected by the magnetic material, and the polarization information of the reflected light is analyzed to form an image.

4. The magneto-optical Kerr measuring device according to claim 1, characterized in that, The underlying chip includes an amplifier circuit, a differential circuit, and a comparator circuit. The dynamic change signal of the imaging optical path intensity is processed by the underlying chip and then output as event information.

5. The magneto-optical Kerr measuring device according to any one of claims 1-4, characterized in that, The event camera is capable of moving vertically and recording the magnetic domain motion process.

6. The magneto-optical Kerr measuring device according to any one of claims 1-4, characterized in that, The event camera acquires event information at a rate of 200 frames per second.

7. The magneto-optical Kerr measuring device according to any one of claims 1-4, characterized in that, The magneto-optical Kerr microscope also includes an LED light source, a beam splitter, a sample holder, an electromagnet, a polarizer, and an analyzer.

8. A method for acquiring images of magnetic domain walls, characterized in that, include: The event camera is mounted on the eyepiece of the magneto-optical Kerr microscope, and the event camera is adjusted to be in a confocal plane with the CMOS camera. The event camera has a light-sensing circuit, which is used to sense dynamic changes in light intensity and output event information, including the movement path of magnetic domains in space and time. The magnetic sample to be tested is fixed on the sample holder of the magneto-optical Kerr microscope; Apply a magnetic field; The light emitted by the light source passes through the polarizer and is linearly polarized, illuminating the surface of the magnetic sample under test. The dynamic changes in the light intensity reflected from the surface of the magnetic sample under test after passing through the analyzer are detected by the event camera, thereby obtaining an image of the magnetic domain walls of the magnetic sample under test.

9. The method for acquiring magnetic domain wall images according to claim 8, characterized in that, The direction of the magnetic field is perpendicular to the surface of the magnetic sample being tested.

10. The method for acquiring magnetic domain wall images according to claim 8, characterized in that, The event camera also performs the following processing: The dynamic changes in light intensity detected by the event camera are converted into electrical signals. The electrical signal is processed by a differential circuit to obtain the change amount; The change is transmitted to the comparison circuit, and the change is compared with a preset threshold. When the change exceeds a preset threshold, event information is output.

11. The method for acquiring magnetic domain wall images according to claim 10, characterized in that, The change refers to the amount of change from the beginning of the previous event information to the present.

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