A magnetic domain detection method using photoinduced anomalous Nernst effect

Abstract

The present invention discloses a magnetic domain detection method utilizing the photoinduced anomalous Nernst effect. The method uses visible light as the detection light, focusing it vertically to irradiate a nanosheet of the material being tested to form a light spot, generating a temperature gradient. This causes carriers around the light spot to diffuse along the temperature gradient, generating a net current locally. Based on the photoinduced anomalous Nernst effect, a photocurrent signal is generated when the light spot irradiates the magnetic domain boundary. The photocurrent signal is collected through source and drain electrodes and transmitted to an external signal processing circuit for amplification. The net current corresponding to the photocurrent is extracted to obtain the photocurrent, and the distribution of the magnetic domains is determined based on the spatial distribution of the photocurrent. The method does not require any special optical path or device structure, and the experimental setup is simple. The method can be used in fields such as material characterization, microscopic detection, and magnetic research, and has broad application prospects in microscopic detection.

Description

Technical Field

[0001] The present invention relates to a magnetic domain detection technology, and in particular to a magnetic domain detection method utilizing a photoinduced anomalous Nernst effect. Background Art

[0002] With the development of various microscopic imaging technologies, our understanding of the microscopic structure of matter has become increasingly clear. Magnetism is one of the fundamental properties of matter, and its microscopic imaging is an important research direction in experimental physics. The rise of fields such as magnetic storage and spin electronics has put forward technical requirements for the microscopic study of magnetism. Currently, the more mature magnetic imaging technologies include magneto-optical Kerr microscopy (MOKE), reflection magnetic circular dichroism (RMCD), Lorentz transmission electron microscopy (L-TEM), magnetic force microscopy (MFM), photoemission electron microscopy (PEEM), and scanning superconducting quantum interference microscopy (SSM). These technologies have their own advantages and limitations due to their different principles.

[0003] For example, the magneto-optical Kerr microscope is based on the magneto-optical Kerr effect, which uses the interaction between light and the magnetic field in magnetic materials and is suitable for magnetic thin film samples; reflection magnetic circular dichroism requires additional polarization modulation means, and the test structure is relatively complex; the Lorentz electron microscope is based on the transmission electron microscope, which is expensive and complicated to operate, and cannot be widely used in the study of magnetic domain structures; magnetic force microscopy measurements are affected by the shape of the needle tip, the properties of the sample, and the distance between the probe and the sample. At the same time, the magnetic needle tip will affect the original magnetic field distribution of the weak magnetic sample, resulting in measurement limitations; the scanning superconducting quantum interference device microscope can be used for quantitative image analysis of the magnetic field distribution in micro-areas on the sample surface and can perform micro-area magnetization performance curve measurements, but it needs to work in a low-temperature environment. Summary of the Invention

[0004] In view of the above problems existing in the prior art, the present invention proposes a magnetic domain detection method using the photoinduced anomalous Nernst effect, which directly detects the magnetic domain of the material using the photoinduced anomalous Nernst effect.

[0005] The magnetic domain detection method using the photoinduced anomalous Nernst effect of the present invention comprises the following steps:

[0006] 1) Preparation for testing:

[0007] The nanosheet of the material to be tested is in the form of a sheet and has a thickness of nanometers. The upper surface of the substrate is non-conductive, and the nanosheet of the material to be tested is disposed on the upper surface of the substrate. A source electrode and a drain electrode are disposed on the substrate and at both ends of the nanosheet of the material to be tested, respectively. The two ends of the nanosheet of the material to be tested are electrically connected to the source electrode and the drain electrode, respectively, and the source electrode and the drain electrode are connected to an external signal processing circuit.

[0008] 2) The detection light is focused onto the nanosheet of the material being tested, forming a light spot on the nanosheet of the material being tested;

[0009] 3) The focused light beam is vertically irradiated onto the nanosheet of the material being tested, and the irradiated area is heated, generating a temperature gradient around the light spot. According to the Seebeck effect, the temperature gradient causes the carriers around the light spot to diffuse along the temperature gradient direction, thereby generating a net current locally in the nanosheet of the material being tested. According to the photoinduced anomalous Nernst effect, the carriers affected by the magnetization of the magnetic domains in the material diffuse laterally along the direction perpendicular to the temperature gradient under the set magnetization. When the light spot is irradiated inside the magnetic domain, the photocurrents generated are symmetrical with the light spot as the center and cancel each other out. When the light spot is irradiated on the boundary of the magnetic domain, the magnetization is reversed, and the same direction current is generated locally. Therefore, when the light spot is irradiated inside the magnetic domain, the photocurrents are mutually canceled out, and when the light spot is irradiated on the boundary of the magnetic domain, the photocurrents are superimposed on each other, thereby generating a photocurrent signal when the light spot is irradiated on the boundary of the magnetic domain.

[0010] 4) The source electrode and the drain electrode collect the photocurrent signal generated by the magnetic domain boundary and convert the photocurrent signal into an electrical signal to be transmitted to the external signal processing circuit; the external signal processing circuit amplifies the electrical signal and extracts the net current corresponding to the photocurrent to obtain the photocurrent;

[0011] 5) Changing the position where the light spot is irradiated onto the material under test, and collecting the generated photocurrent signal by an external signal processing circuit until all positions of the nanosheet of the material under test are two-dimensionally scanned to obtain the spatial distribution of the photocurrent, and then obtaining the distribution of the magnetic domains based on the spatial distribution of the photocurrent.

[0012] Wherein, in step 1), the thickness of the nanosheet of the material to be tested is less than 100 nm.

[0013] The external signal processing circuit includes: a preamplifier, a lock-in amplifier, a data collector, an optical chopper and a computer; the source electrode is connected to the input of the preamplifier, the drain electrode is grounded, the output of the preamplifier is connected to the input of the lock-in amplifier, and the modulation signal end of the optical chopper is connected to the reference signal end of the lock-in amplifier; the output of the lock-in amplifier is connected to the data collector, and the data collector is connected to the computer.

[0014] In step 2), the frequency of the probe light is determined based on the specific material. The frequency of the probe light is greater than the energy gap of the material being measured; the probe light is visible light. The higher the probe light frequency, the smaller the radius of the focused spot. The spot radius is 1-5 μm. The spot radius determines the detection resolution; the smaller the spot radius, the higher the detection resolution. The spot area is smaller than the area of ​​the magnetic domain.

[0015] In step 3), the temperature gradient is related to the power of the probe light, the radius of the spot, and the thermal conductivity of the material: A higher power leads to a larger temperature gradient, a larger spot radius leads to a smaller temperature gradient, and a higher thermal conductivity leads to a smaller temperature gradient. Setting the magnetization means magnetizing the nanosheet perpendicular to the plane of the nanosheet along the direction of the set external magnetic field.

[0016] In step 4), the source electrode and the drain electrode collect the photocurrent signal generated by the magnetic domain boundary, and convert the photocurrent signal into an electrical signal and transmit it to the preamplifier; the preamplifier amplifies the electrical signal; the detection light first passes through the optical chopper and then focuses on the nanosheet of the material to be tested; the optical chopper modulates the light beam passing through the optical chopper at a set frequency, and transmits the modulation frequency to the phase-locked amplifier; the phase-locked amplifier separates the corresponding part of the photocurrent in the electrical signal from the electrical noise according to the modulation frequency provided by the optical chopper, removes the electrical noise in the electrical signal, and thus extracts the net current corresponding to the photocurrent; the phase-locked amplifier transmits the net current corresponding to the photocurrent to the data acquisition device; the data acquisition device converts the electrical signal into a digital signal and transmits it to the computer to obtain the photocurrent.

[0017] In step 5), the position of the light spot on the material being tested is changed by using a motorized translation stage or a galvanometer. A substrate with nanosheets of the material being tested is placed on the motorized translation stage, and the nanosheets are moved using the motorized translation stage. Alternatively, the probe light passes through a galvanometer and is incident on the nanosheets, and the galvanometer controls the propagation direction of the light beam to change the position of the light spot on the material being tested. Each change in the position of the light spot on the material being tested is smaller than the radius of the light spot.

[0018] The center position of the light spot when the photocurrent signal is measured is the position of the photocurrent, and the spatial distribution of the photocurrent is obtained. The position of the photocurrent is the position of the magnetic domain boundary, and the distribution of the magnetic domain is obtained according to the spatial distribution of the photocurrent.

[0019] Advantages of the present invention:

[0020] The present invention detects the magnetic domains of materials based on the photoinduced anomalous Nernst effect; the present invention uses visible light as a light source, does not require a special optical path structure or device structure, and the experimental setup is simple; the method of the present invention can be used in fields such as material characterization, microscopic detection and magnetic research, and has broad application prospects in microscopic detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A schematic diagram of the connection of detection equipment in an embodiment of a method for detecting magnetic domains using the photoinduced anomalous Nernst effect of the present invention;

[0022] Figure 2FIG1 is a connection diagram of an external signal processing circuit of an embodiment of a method for detecting magnetic domains using a photoinduced anomalous Nernst effect according to the present invention;

[0023] Figure 3 A schematic diagram of the distribution of local current density generated by irradiating a light spot onto a nanosheet of a material to be tested according to an embodiment of a magnetic domain detection method using the photoinduced anomalous Nernst effect of the present invention;

[0024] Figure 4 FIG. 1 is a schematic diagram of a net current according to an embodiment of a magnetic domain detection method using the photoinduced anomalous Nernst effect of the present invention. DETAILED DESCRIPTION

[0025] The present invention will be further described below through specific embodiments in conjunction with the accompanying drawings.

[0026] The magnetic domain detection method using the photoinduced anomalous Nernst effect of this embodiment includes the following steps:

[0027] 1) Detection preparation:

[0028] a) Preparation of tested materials:

[0029] The nanosheet 1 of the material to be tested is in sheet shape and made of cobalt tin sulfur Co3Sn2S2 with a thickness of 80nm. The substrate is 500μm thick aluminum oxide Al2O3, and the nanosheet of the material to be tested is set on the upper surface of the substrate. The source electrode 2 and the drain electrode 3 are respectively set on the substrate and at the two ends of the nanosheet of the material to be tested. The source electrode 2 and the drain electrode 3 each include two layers, the lower transition metal layer is Ti with a thickness of 5-10nm, and the upper conductive metal layer is Au with a thickness of 50-100nm.

[0030] nm; the two ends of the nanosheet of the material being tested are electrically connected to the source electrode and the drain electrode respectively, the source electrode is connected to the external signal processing circuit A, and the drain electrode is grounded, such as Figure 1 As shown;

[0031] b) External signal processing circuit connection;

[0032] The external signal processing circuit includes: a preamplifier, a lock-in amplifier, a data collector, an optical chopper and a computer; the drain electrode is grounded, the source electrode is connected to the input of the preamplifier, the output of the preamplifier is connected to the input of the lock-in amplifier, the modulation signal terminal of the optical chopper is connected to the reference signal terminal of the lock-in amplifier; the output of the lock-in amplifier is connected to the data collector, and the data collector is connected to the computer, such as Figure 2 As shown;

[0033] 2) The frequency of the probe light is 532nm, which is larger than the energy gap of cobalt tin sulfur Co3Sn2S2; the probe light first passes through an optical chopper, which modulates the probe light passing through the optical chopper at a set frequency and then focuses it onto the nanosheet of the material being tested, forming a light spot on the nanosheet of the material being tested. The radius of the light spot is 1μm, and the lateral size of the magnetic domain is 10-30μm, which is much larger than the diameter of the light spot. Figure 3 As shown;

[0034] 3) The focused light beam is vertically irradiated onto the nanosheet of the material to be tested, and the irradiated area is heated, generating a set temperature gradient around the light spot; according to the Seebeck effect, the temperature gradient causes the carriers around the light spot to diffuse along the temperature gradient direction, thereby generating a net current density locally in the nanosheet of the material to be tested; according to the photoinduced anomalous Nernst effect, the carriers affected by the magnetization in the material diffuse laterally along the direction perpendicular to the temperature gradient under the set magnetization; when the light spot is irradiated inside the magnetic domain, photocurrents are generated that are centrally symmetric about the center of the light spot and cancel each other out; when the light spot is irradiated at the boundary of the magnetic domain, the magnetization is reversed, and currents in the same direction are generated locally, so that when the light spot is irradiated inside the magnetic domain, the photocurrents are mutually canceled out, and when the light spot is irradiated at the boundary of the magnetic domain, the photocurrents are superimposed on each other, thereby generating a photocurrent signal at the boundary of the magnetic domain; no photocurrent is generated at a location without a magnetic domain;

[0035] 4) The source electrode and the drain electrode collect the photocurrent signal generated by the magnetic domain boundary, and convert the photocurrent signal into an electrical signal and transmit it to the preamplifier; the preamplifier amplifies the electrical signal; the optical chopper transmits the modulation frequency of the detection light to the phase-locked amplifier; the phase-locked amplifier separates the photocurrent corresponding part of the electrical signal from the electrical noise according to the modulation frequency provided by the optical chopper, removes the electrical noise in the electrical signal, and thus extracts the net current corresponding to the photocurrent; the phase-locked amplifier transmits the net current corresponding to the photocurrent to the data acquisition device; the data acquisition device converts the electrical signal into a digital signal and transmits it to the computer to obtain the photocurrent;

[0036] 5) Using an electric translation stage or a galvanometer to control the change of the position of the light spot irradiated onto the material under test, the external signal processing circuit collects the generated photocurrent signal until all positions of the nanosheets of the material under test are two-dimensionally scanned, so that the center position of the light spot when there is a photocurrent signal is measured as the position of the photocurrent, and the spatial distribution of the photocurrent is obtained. The distribution of the magnetic domains is obtained based on the spatial distribution of the photocurrent, and the position of the photocurrent is the position of the magnetic domain boundary.

[0037] Figure 4 The photocurrent response diagram of the cobalt tin sulfur nanosheet is shown. Figure 4As shown, after zero-field cooling, the cobalt-tin-sulfur nanosheets randomly magnetize to produce magnetic domains of varying shapes. Detection of these domains produces distinct photocurrent responses at their boundaries, corresponding to distinct domain distributions. This demonstrates that magnetic domain detection according to the present invention can be used in fields such as material characterization, microscopic probing, and magnetic research, and holds broad application prospects in microscopic measurement.

[0038] Finally, it should be noted that the purpose of disclosing the embodiments is to facilitate a further understanding of the present invention. However, those skilled in the art will appreciate that various substitutions and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the contents disclosed in the embodiments; the scope of protection claimed by the present invention shall be determined by the scope defined in the claims.

Claims

1. A magnetic domain detection method using a photoinduced anomalous Nernst effect, characterized in that: The magnetic domain detection method comprises the following steps: 1) Detection preparation: The nanosheet of the material to be tested is in the form of a sheet and has a thickness of nanometers. The upper surface of the substrate is non-conductive, and the nanosheet of the material to be tested is disposed on the upper surface of the substrate. A source electrode and a drain electrode are disposed on the substrate and at both ends of the nanosheet of the material to be tested, respectively. The two ends of the nanosheet of the material to be tested are electrically connected to the source electrode and the drain electrode, respectively, and the source electrode and the drain electrode are connected to an external signal processing circuit. 2) The detection light is focused onto the nanosheet of the material being tested, forming a light spot on the nanosheet of the material being tested; 3) The focused light beam is vertically irradiated onto the nanosheet of the material being tested, and the irradiated area is heated, generating a temperature gradient around the light spot. According to the Seebeck effect, the temperature gradient causes the carriers around the light spot to diffuse along the temperature gradient direction, thereby generating a net current locally in the nanosheet of the material being tested. According to the photoinduced anomalous Nernst effect, the carriers affected by the magnetization of the magnetic domains in the material diffuse laterally along the direction perpendicular to the temperature gradient under the set magnetization. When the light spot is irradiated inside the magnetic domain, the photocurrents generated are symmetrical with the light spot as the center and cancel each other out. When the light spot is irradiated on the boundary of the magnetic domain, the magnetization is reversed, and the same direction current is generated locally. Therefore, when the light spot is irradiated on the magnetic domain, the photocurrents inside the magnetic domain are mutually canceled out, and when the light spot is irradiated on the boundary of the magnetic domain, the photocurrents are superimposed on each other, thereby generating a photocurrent signal when the light spot is irradiated on the boundary of the magnetic domain. 4) The source electrode and the drain electrode collect the photocurrent signal generated by the magnetic domain boundary and convert the photocurrent signal into an electrical signal to be transmitted to the external signal processing circuit; the external signal processing circuit amplifies the electrical signal and extracts the net current corresponding to the photocurrent to obtain the photocurrent; 5) Changing the position where the light spot is irradiated onto the material under test, and collecting the generated photocurrent signal by an external signal processing circuit until all positions of the nanosheet of the material under test are two-dimensionally scanned to obtain the spatial distribution of the photocurrent, and then obtaining the distribution of the magnetic domains based on the spatial distribution of the photocurrent.

2. The magnetic domain detection method according to claim 1, wherein: In step 1), the thickness of the nanosheet of the material to be tested is less than 100 nm.

3. The magnetic domain detection method according to claim 1, wherein: In step 1), the external signal processing circuit includes: a preamplifier, a phase-locked amplifier, a data collector, an optical chopper and a computer; the source electrode is connected to the input of the preamplifier, the drain electrode is grounded, the output of the preamplifier is connected to the input of the phase-locked amplifier, and the modulation signal terminal of the optical chopper is connected to the reference signal terminal of the phase-locked amplifier; the output of the phase-locked amplifier is connected to the data collector, and the data collector is connected to the computer.

4. The magnetic domain detection method according to claim 1, wherein: In step 2), the greater the frequency of the detection light, the smaller the radius of the light spot formed after focusing.

5. The magnetic domain detection method according to claim 1, wherein: In step 2), the area of ​​the light spot is smaller than the area of ​​the magnetic domain.

6. The magnetic domain detection method according to claim 1, wherein: In step 3), the temperature gradient is related to the frequency and power of the detection light, the radius of the light spot, and the thermal conductivity of the material: the greater the frequency of the detection light, the greater the temperature gradient; the greater the power of the detection light, the greater the temperature gradient; the greater the radius of the light spot, the smaller the temperature gradient; the greater the thermal conductivity of the material, the smaller the temperature gradient.

7. The magnetic domain detection method according to claim 1, wherein: In step 3), setting the magnetization means that the magnetization is along the direction of the set external magnetic field and perpendicular to the plane of the nanosheet.

8. The magnetic domain detection method according to claim 1, wherein: In step 4), the source electrode and the drain electrode collect the photocurrent signal generated by the magnetic domain boundary, and convert the photocurrent signal into an electrical signal and transmit it to the preamplifier; the preamplifier amplifies the electrical signal; the detection light first passes through the optical chopper and then focuses on the nanosheet of the material to be tested; the optical chopper modulates the light beam passing through the optical chopper at a set frequency, and transmits the modulation frequency to the phase-locked amplifier; the phase-locked amplifier separates the corresponding part of the photocurrent in the electrical signal from the electrical noise according to the modulation frequency provided by the optical chopper, removes the electrical noise in the electrical signal, and thus extracts the net current corresponding to the photocurrent; the phase-locked amplifier transmits the net current corresponding to the photocurrent to the data acquisition device; The data collector converts the electrical signal into a digital signal and transmits it to the computer to obtain the photocurrent.

9. The magnetic domain detection method according to claim 1, wherein: In step 5), the substrate prepared with the nanosheets of the material to be tested is placed on an electric translation stage, and the position of the nanosheets of the material to be tested is moved by the electric translation stage, or the detection light is incident on the nanosheets of the material to be tested after passing through a galvanometer, and the propagation direction of the light beam is controlled by the galvanometer to change the position where the light spot irradiates the material to be tested.

10. The magnetic domain detection method according to claim 1, wherein: In step 5), the center position of the light spot with a photocurrent signal is measured as the position of the photocurrent, and the spatial distribution of the photocurrent is obtained. The position of the photocurrent is the position of the magnetic domain boundary, and the distribution of the magnetic domain is obtained according to the spatial distribution of the photocurrent.

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