An NV color center scanning probe, scanning microscope, and magnetic moment measurement method

Abstract

This invention provides an NV center scanning probe, a scanning microscope, and a magnetic moment measurement method. The NV center scanning probe includes a diamond micropillar, an NV center, and a magnetic field shielding layer. The diamond micropillar includes a detection surface and a side surface surrounding the detection surface, with the NV center disposed on the detection surface. The detection surface is oriented in a first direction. The magnetic field shielding layer completely covers the side surface and is used to shield stray magnetic fields from directions other than the first direction. This invention solves the problem in existing scanning NV magnetic microscopes where the NV center senses the global magnetic field, making it difficult to decouple the local magnetic moment distribution of the sample. This significantly improves the accuracy of scanning NV magnetic microscopes in measuring minute magnetic signals on sample surfaces in complex magnetic environments.

Description

Technical Field

[0001] This invention relates to the field of atomic force microscopy, and in particular to an NV color center scanning probe, a scanning microscope, and a method for measuring magnetic moment. Background Technology

[0002] Scanning nitrogen-vacancy (NV) magnetic force microscopy is an advanced magnetic imaging tool based on diamond NV center quantum sensing technology. Its basic principle is to scan a diamond probe containing NV centers to the vicinity of the sample surface, and by detecting the frequency shift of the optically probed magnetic resonance (ODMR) spectrum of the NV centers, the static magnetic field or microwave magnetic field at their location can be sensed, thereby achieving nanometer-resolution imaging of the magnetic field of the sample surface.

[0003] However, existing scanning NV magnetic force microscopy techniques have a fundamental limitation: the NV color center, acting as a point magnetometer, senses the magnetic field as the vector sum of the magnetic fields generated by all magnetic sources on the sample surface. When the sample possesses a highly non-uniform magnetic structure (e.g., the extremely strong magnetic fields of some magnetic nanoparticles or domain walls), "stray" magnetic fields from these strong magnetic regions can significantly contribute to or even dominate the NV color center's signal, even if the NV color center is not directly above these regions. This results in the final magnetic field distribution map being a convolution of the global magnetic field of the sample, rather than a true "local" magnetic field. Inverting the intrinsic magnetic moment distribution (i.e., magnetization distribution) at each point of the sample based on this globally disturbed magnetic field map is a severely ill-posed inverse problem, extremely difficult and inaccurate to solve, severely limiting the application of this technique in quantitative magnetic analysis. Summary of the Invention

[0004] This invention provides an NV center scanning probe, a scanning microscope, and a magnetic moment measurement method. By setting a high permeability thin film shielding structure on the side of the NV center scanning probe, the external transverse interference magnetic field is shielded by the magnetic shunting effect, which effectively suppresses the interference of stray magnetic fields in the non-probe direction on the spin state of the NV center. This solves the problem that existing scanning NV magnetic microscopes are difficult to decouple the local magnetic moment distribution of the sample because the NV center senses the global magnetic field.

[0005] In a first aspect, embodiments of the present invention provide an NV color center scanning probe, comprising a diamond micropillar, an NV color center, and a magnetic field shielding layer; The diamond micropillar includes a probe surface and a side surface surrounding the probe surface, with NV color centers disposed on the probe surface; wherein, the probe surface is oriented in a first direction; The magnetic field shielding layer completely covers the side surface and is used to shield stray magnetic fields from directions other than the first direction.

[0006] Optionally, the magnetic field shielding layer extends beyond the end face of the detection surface along the first direction at one end of the detection surface.

[0007] Optionally, the end of the magnetic field shielding layer closest to the detection surface is flush with the detection surface.

[0008] Optionally, the material of the magnetic field shielding layer is a magnetically conductive material.

[0009] Optionally, the magnetic material can be permalloy, iron-silicon-aluminum alloy or cobalt-based amorphous alloy.

[0010] Optionally, the thickness of the magnetic field shielding layer is from 10 nm to 200 nm.

[0011] In a second aspect, embodiments of the present invention also provide a scanning probe microscope, including an atomic force microscopy system for detecting sample surface morphology information and a photodetector magnetic resonance system for detecting sample surface magnetic field distribution information, wherein the atomic force microscopy system includes the NV color center scanning probe of any one of the first aspects.

[0012] Thirdly, embodiments of the present invention also provide a magnetic moment measurement method, applied to the NV color center scanning probe of any one of the first aspects or the scanning probe microscope of the second aspect, the magnetic moment measurement method comprising: The magnetic field measurements of the sample under test at at least three different detection heights at the target test point are obtained sequentially. Based on a preset magnetic field model, the equivalent magnetic moment of the target test point is calculated using the measured magnetic field value and the corresponding detection height.

[0013] Optionally, the magnetic field measurements of the sample under test at at least three different detection heights at the target test point are obtained sequentially, including: The detection surface is positioned at the first detection height, and the sample to be tested is scanned point by point to obtain the first local magnetic field distribution map. The detection surface is positioned at at least two second detection heights different from the first detection height. At each second detection height, the sample to be tested is scanned point by point to obtain at least two second local magnetic field distribution maps. Extract at least three magnetic field measurements corresponding to the target test point from the first local magnetic field distribution map and at least two second local magnetic field distribution maps.

[0014] Optionally, the preset magnetic field model is a magnetic dipole model, and the magnetic field measurement value B and the detection height h satisfy the formula Where B is the measured magnetic field value, m is the equivalent magnetic moment, and h is the detection height; Based on a preset magnetic field model, the equivalent magnetic moment of the target test point is calculated using magnetic field measurements and the corresponding detection height, including: Based on formula The linear relationship is derived. ;in, These are the linearization characteristics of the magnetic field; Calculate the linearized characteristic quantity K of the magnetic field along the first direction at each detection height; Substitute the linearized magnetic field characteristic quantity K corresponding to at least three different detection heights into the linear relationship, fit it using the least squares method, and solve for the equivalent magnetic moment m of the target test point along the first direction.

[0015] Optionally, the detection height can be selected in the range of 5nm to 100nm.

[0016] Optionally, at least three different detection heights can form an arithmetic sequence.

[0017] This invention provides an NV color center scanning probe, a scanning microscope, and a magnetic moment measurement method. By setting a high-permeability thin-film shielding structure on the side of the NV color center scanning probe, the external transverse interference magnetic field is shielded using the magnetic shunting effect, allowing only the effective local magnetic field signal of the sample to be acquired. By scanning and measuring this local magnetic field at different heights, and using a physical model of magnetic dipole field decay with distance for fitting and inversion, the magnetic moment vector and even the magnetic susceptibility of this local region on the sample surface can be accurately calculated. This solves the core problems of traditional nanomagnetic probes, such as weak anti-interference, poor accuracy, and signal distortion, and greatly improves the measurement accuracy of small magnetic signals on the sample surface by scanning NV magnetic force microscopy in complex magnetic environments. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of an NV color center scanning probe provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of another NV color center scanning probe provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of a diamond micropillar provided in an embodiment of the present invention; Figure 4 This is a flowchart illustrating a magnetic moment measurement method provided in an embodiment of the present invention. Figure 5 A flowchart illustrating another magnetic moment measurement method provided in an embodiment of the present invention; Figure 6 This is a flowchart illustrating another magnetic moment measurement method provided in an embodiment of the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be fully described below with reference to the accompanying drawings in the embodiments of this invention, through specific implementation methods. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort fall within the protection scope of this invention.

[0020] Figure 1 This is a schematic diagram of an NV color center scanning probe provided in an embodiment of the present invention. The NV color center scanning probe provided in this embodiment can be specifically applied in scenarios such as nanoscale magnetic imaging, quantum sensing, and material magnetic domain detection. It is used to achieve high-sensitivity, high spatial resolution fixed-point or fixed-region magnetic field detection, and is particularly suitable for the precise measurement of minute magnetic signals on the sample surface in complex magnetic environments (e.g., characterizing the micro-area magnetic moment distribution, magnetic domain structure, interface and defect magnetic distortion of materials such as CoFeB soft magnetic films and NdFeB permanent magnet particles, and tracking the evolution of micro-area magnetization reversal under external fields). Reference Figure 1 An NV color center scanning probe provided in this embodiment of the invention includes a diamond micropillar 10, an NV color center 11, and a magnetic field shielding layer 20; The diamond micropillar 10 includes a detection surface 12 and a side surface 13 surrounding the detection surface, and an NV color center 11 is disposed on the detection surface 12. The magnetic field shielding layer 20 completely covers the side surface 13 and is used to shield stray magnetic fields from directions other than the first direction.

[0021] Among them, the detection surface 12 faces the first direction y, which can be understood as the direction in which the detection surface faces, usually pointing to the sample to be tested 1, that is, the main axis direction of the NV color center for magnetic field detection.

[0022] Specifically, when the NV center scanning probe scans the surface of the sample 1, the target magnetic field (along the first direction y) from the sample 1 acts on the NV center 11 on the detection surface 12. Meanwhile, stray magnetic fields from the sides are attracted by the high-permeability magnetic field shielding layer 20. Because the magnetic field shielding layer 20 has high permeability, magnetic field lines preferentially pass through the interior of the magnetic field shielding layer 20, thereby significantly reducing the transverse magnetic field component reaching the NV center 11 on the detection surface 12.

[0023] This invention, through the provision of a high-permeability thin-film shielding structure on the side of the NV color center scanning probe, utilizes the magnetic shunting effect to shield external transverse interference magnetic fields. This effectively suppresses the interference of stray magnetic fields from non-detection directions on the spin state of the NV color center, improves the signal-to-noise ratio and directional selectivity of magnetic field detection, and effectively solves the core problems of traditional nanomagnetic detection such as weak anti-interference, poor accuracy, and signal distortion. It greatly improves the spatial magnetic field resolution and quantitative analysis capability of magnetic moment in scanning NV magnetic force microscopes.

[0024] Figure 2 This is a schematic diagram of another NV color center scanning probe provided in an embodiment of the present invention. Figure 3 This is a schematic diagram of a diamond micropillar provided in an embodiment of the present invention, with reference to... Figure 2 and Figure 3In an optional embodiment, the magnetic field shielding layer 20 extends beyond the end face of the detector surface 12 along the first direction y at one end near the detector surface 12.

[0025] For example, refer to Figure 2 and Figure 3 At the top of the diamond micropillar 10, the magnetic field shielding layer 20 does not terminate at the plane where the probe surface 12 is located, but extends further beyond the side surface 13 by a first preset distance L. During actual scanning, the NV center scanning probe may need to be raised to different detection heights for multi-height magnetic field measurements. When the probe surface 12 is far from the sample surface, the detection range of the NV center 11 expands conically with increasing height. If the magnetic field shielding layer 20 is only flush with the side surface 13, its lateral shielding effect on the NV center will weaken with increasing detection height. Extending the magnetic field shielding layer 20 beyond the side surface 13 by a distance L towards the probe surface 12 is equivalent to forming a shielding barrier above the side of the NV center 11. Even if the probe surface is raised to a certain height, the NV center 11 remains within the effective shielding range of the magnetic field shielding layer 20, thus effectively intercepting magnetic field lines from directions other than the first direction y and reducing stray magnetic field interference. The specific value of the first preset distance L can be determined by comprehensive optimization based on the probe's working height range, the magnetic permeability of the shielding layer material, and the micro / nano fabrication precision.

[0026] Furthermore, this application does not limit the extension direction of the magnetic field shielding layer 20. For example, it can extend along the side surface 13 of the diamond micropillar 10, or along the first direction y. Regardless of the extension direction, the purpose is to form an effective magnetic shielding structure around the NV color center 11 to suppress the interference of stray magnetic fields from non-detection directions on quantum sensing. The specific choice of extension direction can be optimized based on the convenience of micro / nano fabrication technology, the mechanical stability of the probe, the spatial distribution of the required shielding effect, and the actual application scenario. Those skilled in the art can reasonably design the extension direction and coverage of the magnetic field shielding layer 20 according to specific needs, and these variations all fall within the protection scope of this application.

[0027] Continue to refer to Figure 1 In an optional embodiment, the magnetic field shielding layer 20 is flush with the end of the detector surface 12 near the detector surface 12.

[0028] Specifically, the magnetic field shielding layer 20 is flush with the detector surface 12 at one end. That is, the shielding layer 20 completely covers the side surface 13, shielding it from stray magnetic fields from the side and preventing magnetic field lines from diffracting from the side surface 13 into the region where the NV color center 11 is located. Furthermore, the magnetic field shielding layer 20 does not extend beyond the detector surface 12, avoiding physical obstruction or near-field magnetic interference of the shielding material on the detector surface 12 itself (i.e., the region where the NV color center 11 is located), ensuring that the probe can approach the sample surface as close as possible and maintain nanometer-level spatial resolution. Simultaneously, the flush design simplifies micro / nano fabrication processes. Compared to the previous embodiment, the flush design focuses more on achieving basic lateral magnetic shielding functionality while minimizing probe size and process complexity.

[0029] It should be noted that in actual measurements, the closer the NV color center 11 is to the surface of the sample 1, the higher its detection sensitivity. Furthermore, due to the extremely small distance between the NV color center 11 and the sample 1, the relative proportion of stray magnetic fields from the sides decreases, and the requirement for magnetic shielding is correspondingly lower. However, as the detection distance increases (e.g., to perform multi-height magnetic field measurements or to avoid probe collisions with rough samples, the probe is raised to 50nm-100nm), the interference of stray magnetic fields from the sides on the NV color center 11 gradually increases. As the probe moves away from the sample surface, the angle change and spatial attenuation rate between the laterally incident magnetic field lines and the NV color center 11 differ, leading to a relative increase in the contribution of magnetic noise from non-detection directions. Therefore, in applications requiring a large dynamic range detection height (e.g., 50nm-100nm), a longer magnetic field shielding layer 20 is recommended to ensure that the edge of the shielding layer can still effectively intercept stray magnetic fields from the sides at the highest detection height. Conversely, if the probe primarily operates in very close-range contact or quasi-contact mode and has a small scanning range, a design flush with the detection surface 12 can be used to simplify the manufacturing process and reduce probe weight. Those skilled in the art can flexibly select the shielding layer's coverage length based on the actual detection height range, environmental magnetic noise level, and microfabrication capabilities.

[0030] Optionally, the material of the magnetic field shielding layer 20 is a magnetically conductive material.

[0031] Specifically, the magnetically conductive material has high permeability and low coercivity, which can effectively absorb stray magnetic fields from directions other than the first direction y and make the magnetic field lines preferentially pass through the inside of the magnetic field shielding layer 20, rather than passing through the magnetic field shielding layer 20 to reach the NV color center 11 on the detection surface 12.

[0032] In one specific embodiment, the magnetic material is permalloy, iron-silicon-aluminum alloy, or cobalt-based amorphous alloy. Permalloy has extremely high initial permeability and extremely low coercivity, making it particularly suitable as a magnetic field shielding layer 20 in weak magnetic field environments, enabling efficient magnetic flux shunting with minimal external magnetic field drive. Iron-silicon-aluminum alloy has high saturation magnetization and resistivity, making it suitable for applications with strong external magnetic fields or high frequencies. Cobalt-based amorphous alloy has a near-zero magnetostriction coefficient, maintaining excellent soft magnetic properties under mechanical stress, making it suitable for fabricating conformal magnetic field shielding layers 20 in complex microfabrication processes, especially for uniform coating of the side surface 13 of diamond micropillars 10.

[0033] Optionally, the thickness of the magnetic field shielding layer 20 is from 10 nm to 200 nm.

[0034] Specifically, when the thickness is less than 10 nm, the magnetic field shielding layer 20 may have discontinuities, island-like growth, or pinhole defects due to its thinness, resulting in a significant decrease in magnetic permeability and an inability to effectively divert lateral stray magnetic fields. When the thickness is greater than 200 nm, on the one hand, the deposition stress increases, which may lead to a decrease in the adhesion between the magnetic field shielding layer 20 and the side surface 13 of the diamond micropillar 10 or even peeling off. On the other hand, an excessively thick magnetic field shielding layer 20 will increase the overall mass of the probe, which may affect the mechanical resonant frequency of the micropillar. At the same time, it may increase the remanence and hysteresis effect of the magnetic field shielding layer 20 itself, causing additional interference to the NV color center 11.

[0035] This invention also provides a scanning probe microscope, comprising an atomic force microscopy system for detecting sample surface morphology information and a photodetector magnetic resonance system for detecting sample surface magnetic field distribution information. The atomic force microscopy system includes an NV color center scanning probe as described in the first aspect. Therefore, this scanning probe microscope also possesses all the beneficial effects of the aforementioned NV color center scanning probe.

[0036] Figure 4 This is a flowchart illustrating a magnetic moment measurement method provided in an embodiment of the present invention. (Refer to...) Figure 4 The present invention also provides a magnetic moment measurement method, applied to the NV color center scanning probe or scanning probe microscope of any of the above embodiments, the magnetic moment measurement method comprising: S110. Sequentially acquire the magnetic field measurement values ​​of the sample to be tested at at least three different detection heights at the target test point.

[0037] Wherein, the detection height h can be understood as the vertical distance between the detection surface 12 of the NV color center scanning probe and the surface of the sample 1 to be tested; the magnetic field measurement value can be understood as the magnetic field strength value Bz at the target test point on the surface of the sample 1 to be tested at the corresponding detection height, which is measured by NV color center optically detected magnetic resonance (ODMR).

[0038] Specifically, the detection surface 12 of the NV center scanning probe is aligned with a target test point of the sample 1 to be tested, and the NV center scanning probe is sequentially positioned at at least three different detection heights (e.g., h1, h2, h3, such as 10nm, 20nm, 50nm). At each height, the resonant frequency shift of the NV center 11 is obtained by ODMR measurement, and the magnetic field measurement value Bi (i=1,2,3) at that height is calculated and recorded.

[0039] S120. Based on a preset magnetic field model, the equivalent magnetic moment of the target test point is calculated using the measured magnetic field value and the corresponding detection height.

[0040] Among them, the preset magnetic field model can be understood as a mathematical model describing the attenuation of the magnetic field generated by a point or tiny magnetic source in space with distance, such as a magnetic dipole or a higher-order magnetic multipole magnetic field model; the equivalent magnetic moment can be understood as the magnitude of the magnetic moment of a point magnetic dipole located on the surface of the sample 1, which is equivalent to the local magnetism of the sample 1 at the target test point.

[0041] Specifically, the measured magnetic field values ​​(Bi, hi) at at least three different heights are substituted into a pre-defined magnetic field model. By fitting or solving the system of equations, the equivalent magnetic moment m at the target test point is obtained.

[0042] It should be noted that in actual measurements, the total distance h between the NV color center 11 and the sample 1 under test consists of three parts: the depth h of the NV color center 11 below the detection surface 12. 01 Feedback height error h of atomic force microscope 02 And the detection height hi. Therefore, the total distance can be expressed as h = h 01 +h 02 +hi = h0 + hi, where h0 = h 01 +h 02It is impossible to measure directly and accurately. Due to the existence of h0, if the magnetic moment is calculated directly using only the magnetic field measurement value at a single detection height, a significant systematic error will occur. In addition, there will also be corresponding operational errors and equipment accuracy errors during equipment operation. The embodiments of the present invention use at least three magnetic field measurement values ​​(h1, B1), (h2, B2), and (h3, B3) at different detection heights, and substitute them into a preset magnetic field model for fitting or solving equations. The unknown constant h0 can be eliminated during the fitting process, thereby eliminating the systematic error caused by the uncertainty of the absolute distance between the probe and the sample 1. Furthermore, multi-point measurement is used to improve the accuracy and robustness of magnetic moment inversion.

[0043] Figure 5 This is a flowchart illustrating another magnetic moment measurement method provided in an embodiment of the present invention. Regarding the above embodiment, "S110, sequentially acquiring the magnetic field measurement values ​​of the sample to be tested at at least three different detection heights at the target test point" can be further refined as follows: The detection surface is positioned at the first detection height, and the sample to be tested is scanned point by point to obtain the first local magnetic field distribution map. The detection surface is positioned at at least two second detection heights different from the first detection height. At each second detection height, the sample to be tested is scanned point by point to obtain at least two second local magnetic field distribution maps. Extract at least three magnetic field measurements corresponding to the target test point from the first local magnetic field distribution map and at least two second local magnetic field distribution maps.

[0044] like Figure 5 As shown, another magnetic moment measurement method provided by this embodiment of the invention may include the following specific steps: S211. Position the detection surface at the first detection height, scan the sample to be tested point by point, and obtain the first local magnetic field distribution map.

[0045] The first detection height can be understood as the initially set distance between the probe and the sample 1 to be tested; the first local magnetic field distribution map can be understood as a two-dimensional magnetic field image measured at the first detection height.

[0046] Specifically, the detection surface 12 of the NV color center scanning probe is positioned at the first detection height, and then the test area of ​​the test sample 1 (the projection area of ​​the detection surface 12 on the test sample 1 along the first direction y) is scanned point by point. ODMR signals are collected at each pixel and the magnetic field value is calculated, and finally the first local magnetic field distribution map is generated.

[0047] S212. Position the detection surface at at least two second detection heights different from the first detection height, and scan the sample to be tested point by point at each second detection height to obtain at least two second local magnetic field distribution maps.

[0048] The second detection height can be understood as a different height than the first detection height, either raised or lowered.

[0049] Specifically, the detection surface 12 is raised to at least two different second detection heights in sequence, and the test area of ​​the sample 1 is scanned point by point at each height to obtain the corresponding second local magnetic field distribution map.

[0050] S213. Extract at least three magnetic field measurement values ​​corresponding to the target test point from the first local magnetic field distribution map and at least two second local magnetic field distribution maps.

[0051] The target test point can be understood as a specific coordinate point selected in the first local magnetic field distribution map.

[0052] Specifically, firstly, one or more target test points are selected from the first local magnetic field distribution map. Then, in the corresponding second local magnetic field distribution map, the magnetic field measurement values ​​B1, B2, and B3 of that point, as well as the corresponding detection heights h1, h2, and h3, are extracted respectively.

[0053] S220. Based on a preset magnetic field model, the equivalent magnetic moment of the target test point is calculated using the measured magnetic field value and the corresponding detection height.

[0054] Figure 6 This is a flowchart illustrating another magnetic moment measurement method provided in an embodiment of the present invention. In the above embodiment, the preset magnetic field model is a magnetic dipole model, and the measured magnetic field value B and the detection height h satisfy the formula... Where B is the measured magnetic field value, m is the equivalent magnetic moment, and h is the detection height; "S120. Based on a preset magnetic field model, calculate the equivalent magnetic moment of the target test point using the measured magnetic field value and the corresponding detection height" can be further refined as follows: Based on formula The linear relationship is derived. ;in, These are the linearization characteristics of the magnetic field; Calculate the linearized characteristic quantity K of the magnetic field along the first direction at each detection height; Substitute the linearized magnetic field characteristic quantity K corresponding to at least three different detection heights into the linear relationship, fit it using the least squares method, and solve for the equivalent magnetic moment m of the target test point along the first direction.

[0055] like Figure 6 As shown, another magnetic moment measurement method provided by this embodiment of the invention may include the following specific steps: S310. Sequentially acquire the magnetic field measurement values ​​of the sample to be tested at at least three different detection heights at the target test point.

[0056] S321, Based on Formula The linear relationship is derived. .

[0057] in, This is a characteristic quantity for linearizing the magnetic field.

[0058] Specifically, assuming the particle can be considered as a point magnetic dipole, and the preset magnetic field model is a magnetic dipole model, it is assumed that the local magnetic source of the sample at the target test point can be equivalent to a vertically magnetized point magnetic dipole, and the vertical magnetic field component B (i.e., the magnetic field measurement value) generated by it satisfies the formula with the detection height h. μ0 is the free permeability (4π×10⁻⁶). -7 N / A 2 m is the equivalent magnetic moment, and h is the distance between the probe surface 12 and the sample 1 to be tested. The linearization characteristic quantity K of the magnetic field is linearly related to h. The intercept and slope can be obtained by linear fitting, and then m and h can be calculated.

[0059] S322. Calculate the linearized characteristic quantity K of the magnetic field along the first direction at each detection height.

[0060] Specifically, for each detection height hi (i=1,2,3), the magnetic field linearization characteristic Ki corresponding to the magnetic field measurement value Bi is calculated.

[0061] S323. Substitute the linearized magnetic field characteristic quantity K corresponding to at least three different detection heights into the linear relationship, fit it using the least squares method, and solve for the equivalent magnetic moment m of the target test point along the first direction y.

[0062] Specifically, substitute at least three data points (hi, Ki) into the linearized relation. By fitting the data using the nonlinear least squares method, the parameters h and m that minimize the sum of squared residuals are solved, thereby obtaining the equivalent magnetic moment m of the target test point.

[0063] Optionally, the detection height can be selected in the range of 5nm to 100nm.

[0064] Specifically, the detection height can be selected within the range of 5nm to 100nm, such as 80nm, 90nm, 100nm or 30nm, 40nm, 50nm, etc. Furthermore, in actual measurements, the probe tip should be adjusted to be as close as possible to the surface of the sample 1 under test. Therefore, a scheme where the detection height is consistently within 50nm (e.g., 10nm, 20nm, 30nm) is preferred. When the detection height is too small (<5nm), the probe may be at risk of collision due to surface adsorption layers, particulate contamination, or the surface roughness of the sample 1 under test, and the NV color center signal may saturate due to near-field effects, affecting the linear response of the magnetic field. When the detection height is too large (>100nm), the magnetic field signal attenuates with the cube of the distance, the signal-to-noise ratio decreases significantly, and the accuracy of the equivalent magnetic moment inversion is affected. Controlling the detection height within 50nm allows for a sufficiently strong magnetic field signal while ensuring the probe safely approaches the surface of the sample 1 under test, and the magnetic dipole model can still describe the field distribution of the point magnetic source well within this distance range.

[0065] Optionally, at least three different detection heights can form an arithmetic sequence.

[0066] Specifically, at least three different detection heights are preferably arranged in an arithmetic sequence, for example, h1=10nm, h2=20nm, h3=30nm (tolerance Δh=10nm), or h1=20nm, h2=40nm, h3=60nm (tolerance Δh=20nm). Using an arithmetic sequence for the detection heights allows for more uniform coverage of the target height range in subsequent nonlinear fitting based on the magnetic dipole model (such as the least squares method), avoiding overfitting or extrapolation errors caused by sampling points clustering in a certain interval. Furthermore, after linearizing the model using variable substitution, the arithmetic sequence of detection heights facilitates rapid calculation of the magnetic moment m through simple linear regression (such as calculating the intercept and slope), simplifying the calculation process. In addition, the arithmetic sequence also facilitates direct estimation of the magnetic field attenuation gradient through the differences in the arithmetic sequence, aiding in verifying the self-consistency of the measurement data.

[0067] In an optional embodiment, after calculating the equivalent magnetic moment of the target test point based on a preset magnetic field model, using the magnetic field measurement value and the corresponding detection height, the method further includes: calculating the magnetic susceptibility of the region corresponding to the target test point based on the equivalent magnetic moment and the external magnetic field acting on the sample to be tested.

[0068] The external magnetic field can be understood as a known constant or alternating magnetic field H applied to the sample 1 to be measured by an external coil during the measurement process.

[0069] Specifically, after obtaining the equivalent magnetic moment m of the target test point through the aforementioned magnetic moment measurement method, given the applied magnetic field H and the effective volume V of the magnetic nanoparticles or magnetic materials in the region corresponding to the target test point, the magnetic susceptibility χ = m / (V×H) can be obtained by back-deriving the relationship m = V×χ×H and then calculated.

[0070] The above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, combinations, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. An NV color center scanning probe, characterized in that, Includes diamond micropillars, NV color centers, and magnetic field shielding layers; The diamond micropillar includes a detection surface and a side surface surrounding the detection surface, and the NV color center is disposed on the detection surface; wherein the orientation of the detection surface is a first direction; The magnetic field shielding layer completely covers the side surface and is used to shield stray magnetic fields from directions other than the first direction.

2. The NV color center scanning probe according to claim 1, characterized in that, The magnetic field shielding layer extends beyond the end face of the detection surface along the first direction, near one end of the detection surface.

3. The NV color center scanning probe according to claim 1, characterized in that, The magnetic field shielding layer is flush with the end of the detection surface near the detection surface.

4. The NV color center scanning probe according to claim 1, characterized in that, The material of the magnetic field shielding layer is a magnetically conductive material.

5. The NV color center scanning probe according to claim 4, characterized in that, The magnetically conductive material is permalloy, iron-silicon-aluminum alloy, or cobalt-based amorphous alloy.

6. The NV color center scanning probe according to claim 1, characterized in that, The thickness of the magnetic field shielding layer is 10 nm to 200 nm.

7. A scanning probe microscope, characterized in that, It includes an atomic force microscopy system for detecting sample surface morphology information and a photodetector magnetic resonance system for detecting sample surface magnetic field distribution information, wherein the atomic force microscopy system includes the NV color center scanning probe according to any one of claims 1-6.

8. A method for measuring magnetic moment, characterized in that, The magnetic moment measurement method, applied to the NV color center scanning probe of any one of claims 1 to 6 or the scanning probe microscope of claim 7, comprises: The magnetic field measurements of the sample under test at at least three different detection heights at the target test point are obtained sequentially. Based on a preset magnetic field model, the equivalent magnetic moment of the target test point is calculated using the measured magnetic field value and the corresponding detection height.

9. The magnetic moment measurement method according to claim 8, characterized in that, The magnetic field measurements of the sample under test at at least three different detection heights at the target test point are obtained sequentially, including: The detection surface is positioned at the first detection height, and the sample to be tested is scanned point by point to obtain the first local magnetic field distribution map; The detection surface is positioned at at least two second detection heights different from the first detection height, and the sample to be tested is scanned point by point at each second detection height to obtain at least two second local magnetic field distribution maps. From the first local magnetic field distribution map and at least two of the second local magnetic field distribution maps, extract at least three magnetic field measurement values ​​corresponding to the target test point.

10. The magnetic moment measurement method according to claim 8, characterized in that, The preset magnetic field model is a magnetic dipole model, and the measured magnetic field value and the detection height satisfy the formula. Where B is the measured magnetic field value, m is the equivalent magnetic moment, and h is the detection height; Based on a preset magnetic field model, the equivalent magnetic moment of the target test point is calculated using the measured magnetic field value and the corresponding detection height, including: Based on formula The linear relationship is derived. ;in, These are the linearization characteristics of the magnetic field; Calculate the linearized characteristic quantity K of the magnetic field along the first direction at each of the aforementioned detection heights; Substitute the linearized magnetic field characteristic quantity K corresponding to at least three different detection heights into the linear relationship, fit it using the least squares method, and solve for the equivalent magnetic moment m of the target test point along the first direction.

11. The magnetic moment measurement method according to claim 8, characterized in that, The detection height is selected within the range of 5nm to 100nm.

12. The magnetic moment measurement method according to claim 8, characterized in that, The at least three different detection heights form an arithmetic sequence.

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