Weak magnetic detection sensor and system based on plane Hall effect and application

Abstract

The invention relates to the technical field of magnetic detection, in particular to a weak magnetic detection sensor and system based on a plane Hall effect and application. The detection sensor comprises a data acquisition board, a detection chip and a magnetic flux collector; the detection chip comprises a substrate and an elliptical Hall device arranged on the substrate, and the Hall device comprises a heavy metal layer Ta, a magnetic thin film layer and a heavy metal n layer Pt; ta and Pt on the upper side and the lower side of the magnetic thin film layer have high charge-spin conversion efficiency and spin Hall angles with opposite signs, a remarkable spin current can be generated in the structure by injecting the spin current in the same spin polarization direction, large spin Hall magnetoresistance is caused, and high-sensitivity magnetic field response is achieved through cooperative enhancement; the magnetic flux gathering piece on the short axis side of the Hall device can directionally amplify the magnetic field in the short axis direction of the Hall device, the sensitivity of the detection sensor is further improved on the premise that the signal-to-noise ratio is not sacrificed, and pT-magnitude detection precision is achieved.

Description

Technical Field

[0001] This invention relates to the field of magnetic detection technology, and in particular to a weak magnetic detection sensor, system, and application based on the planar Hall effect. Background Technology

[0002] Concrete structures dominate civil engineering projects due to their advantages in material sourcing, cost, and maintenance. However, magnetic particles inevitably mix into concrete. These particles may originate from extremely weak magnetic components in the raw materials or from weak magnetic particles introduced during the production process by metal tools such as mixers.

[0003] For places with strict requirements for magnetic field environment, such as precision instrument laboratories and special defense facilities, the magnetism of concrete can directly affect the functionality of the structure. Therefore, dynamic detection of weak magnetism in concrete and its raw materials is very important.

[0004] In practical applications, only qualitative judgments can be made regarding the extremely weak magnetism that may exist in concrete raw materials, as well as the weak magnetic particles that may be mixed in during the production process. Quantitative measurement of the magnitude of the magnetism is not possible. Because the magnetism of magnetic particles is as low as the pT level, it is extremely weak, and currently there is no method to accurately detect and quantitatively measure such weak magnetism.

[0005] Currently available planar Hall effect devices include two-layer, three-layer, and multi-layer thin-film structures. Two-layer structures consist of a magnetic thin-film layer and a protective layer on top of it. The magnetic thin-film layer is in direct contact with the substrate, which leads to a decrease in the growth quality of the magnetic thin-film material and a reduction in anisotropic magnetoresistance (AMR). Three-layer structures include a buffer layer, a magnetic thin-film layer, and a protective layer. The Ta / FeNi / Ta three-layer structure is the most widely studied, with the upper and lower Ta layers having the same thickness and symmetrically distributed on both sides of the FeNi layer. This symmetry... This results in the spin currents induced by the spin Hall effect (SHE) in the upper and lower Ta layers exhibiting characteristics of equal magnitude and opposite direction in the FeNi layer. That is, when a charge current is introduced along the in-plane direction of the film, the upper and lower Ta layers will inject spin currents in opposite directions at their interfaces with FeNi. These two spin currents superimpose and completely cancel each other in the FeNi layer, resulting in zero net spin current accumulation in the FeNi layer. The spin Hall magnetoresistance (SMR) effect and spin torque (SOT) effect associated with the spin current are strongly suppressed and cannot be observed in the system.

[0006] Therefore, developing a sensor capable of accurately detecting and quantitatively measuring weak magnetic fields in concrete is of great significance for improving the quality of concrete applications in precision engineering and ensuring the normal operation of special facilities. Summary of the Invention

[0007] To address one of the problems existing in the prior art, the present invention provides a low-magnetism detection sensor, system, and application based on the planar Hall effect, which features high precision, synergistic enhancement of anisotropic magnetoresistance and spin Hall magnetoresistance, and is capable of dynamically monitoring weak remanent magnetism in concrete.

[0008] On one hand, the present invention provides a weak magnetic field detection sensor based on the planar Hall effect, comprising: The data acquisition board has a current input port and a voltage output port; The detection chip includes a substrate disposed on the data acquisition board and an elliptical Hall device laid on the upper surface of the substrate; the Hall device is provided with a plurality of metal electrodes, which are respectively connected to the current input port and the voltage output port; A magnetic flux concentrator is disposed on the data acquisition board. The magnetic flux concentrator includes magnetic flux concentrating plates disposed on both sides of the Hall device with the major axis of the Hall device as the axis of symmetry. The magnetic flux concentrating plates are isosceles trapezoidal structures. The extension line of the minor axis of the Hall device passes through the midpoint of the upper and lower bases of the isosceles trapezoidal structure in sequence. The magnetic flux concentrating plates are used to directionally amplify the magnetic field in the direction of the minor axis of the Hall device.

[0009] The weak magnetic field detection sensor in this technical solution adopts an elliptical Hall device with shape anisotropy along the major axis. By placing the magnetic flux concentrator at both ends of the minor axis of the Hall device, the magnetic field in the minor axis direction can be amplified in a directional manner. This can effectively concentrate the weak magnetic field in space, enhance the magnetic flux density at both ends of the minor axis of the Hall device, and does not increase the detection noise. Without sacrificing the signal-to-noise ratio, the sensitivity of the detection sensor is further improved, achieving detection accuracy on the order of pT.

[0010] In some embodiments of this application, the ratio of the major axis to the minor axis of the Hall device is 6:1. This aspect ratio greatly enhances the Hall device's response to weak magnetic fields, enabling it to achieve ultra-high detection sensitivity. If the aspect ratio is too large, an excessively strong demagnetizing field will be generated, which will "lock" the magnetic moment too firmly in the direction of the major axis, resulting in a weakening of its response to weak magnetic fields in the direction of the minor axis, thus causing a decrease in detection sensitivity. If the aspect ratio is too small, the shape anisotropy equivalent field along the direction of the major axis will be significantly weakened, which may not only disrupt the single-domain state that maintains high sensitivity, but may even cause the magnetic anisotropy along the direction of the major axis to disappear, making it impossible for the sensor to effectively realize the function of detecting weak magnetic fields along the direction of the minor axis.

[0011] In some embodiments of this application, the Hall device comprises heavy metals sequentially along a direction perpendicular to the substrate. Layer, magnetic thin film layer, heavy metal П layer, wherein the heavy metal The layer material is Ta, the heavy metal П layer material is Pt, and the magnetic thin film layer is FeNi. Utilizing the high charge-spin conversion efficiency of Ta and Pt and their opposite-signed spin Hall angles, they are placed on the upper and lower sides of the magnetic thin film layer, respectively. Spin currents with the same spin polarization direction are injected into the magnetic thin film layer, generating a significant spin current in this three-layer film structure. This spin current can induce a large spin Hall magnetoresistance, and its magnetic field angle dependence is consistent with the anisotropic magnetoresistance in the magnetic thin film layer. Therefore, Ta and Pt can synergistically enhance the high-sensitivity magnetic field response.

[0012] In some embodiments of this application, the thickness of the buffer layer and the protective layer is 5 nm, and the thickness of the magnetic thin film layer is 50 nm.

[0013] In some embodiments of this application, the flux concentrator is made of permalloy, which has high permeability and can concentrate the magnetic field in the detection area while avoiding the introduction of additional circuit noise, thereby further improving the detection accuracy of the Hall device.

[0014] In some embodiments of this application, the metal electrode is a gold electrode.

[0015] In some embodiments of this application, the heavy metal The Hall device is fabricated by depositing the magnetic thin film layer, the heavy metal Π layer, and the magnetic thin film layer onto the substrate using a magnetron sputtering process. A gold thin film is grown on the protective layer by magnetron sputtering, and a gold electrode is fabricated using a lift-off process to make the detector chip. The detector chip was annealed in a vacuum at 200°C for 1 hour to crystallize each thin film layer, release interlayer stress, and further improve soft magnetic properties.

[0016] On the other hand, the present invention also provides a weak magnetic field detection system, including a current source, a nanovoltmeter, a host computer, and the aforementioned detection sensor; the current source is connected to the current input port of the detection sensor to provide current to the detection sensor; the nanovoltmeter is connected to the voltage output port of the detection sensor to collect the Hall voltage signal generated by the detection sensor; the host computer is connected to the nanovoltmeter, and the host computer reads the voltage data detected by the nanovoltmeter and analyzes and processes the voltage data to obtain magnetic field strength data.

[0017] In some embodiments of this application, a preamplifier is provided between the nanovoltmeter and the voltage output port. The preamplifier amplifies the Hall voltage generated by the detection sensor, and the nanovoltmeter collects the amplified Hall voltage data to further improve the detection accuracy.

[0018] On the other hand, the present invention also provides an application of the above-mentioned weak magnetic detection sensor in the magnetic detection of concrete and its raw materials, wherein the concrete raw material to be tested is placed above the above-mentioned detection sensor for the magnetic detection of the concrete raw material, or the detection sensor is pre-embedded in the concrete to measure the magnetic properties of the concrete.

[0019] Based on the above technical solution, the weak magnetic detection sensor of the present invention utilizes the high charge-spin conversion efficiency of Ta and Pt and their opposite spin Hall angles, placing them on the upper and lower sides of a magnetic thin film layer respectively, and injecting spin currents with the same spin polarization direction into the magnetic thin film layer, which can generate significant spin currents in the three-layer film structure; this spin current can induce a large spin Hall magnetoresistance, and its magnetic field angle dependence is consistent with the anisotropic magnetoresistance in the magnetic thin film layer. Therefore, Ta and Pt can synergistically enhance the high-sensitivity magnetic field response. By using an elliptical Hall device and placing the magnetic flux concentrator at both ends of the short axis of the Hall device, the magnetic field in the short axis direction can be amplified in a directional manner, enhancing the magnetic flux density at both ends of the short axis of the Hall device without increasing the detection noise. This further improves the sensitivity of the detection sensor without sacrificing the signal-to-noise ratio, achieving a detection accuracy on the order of pT. While amplifying the effective signal, the preamplifier can suppress the introduction of additional noise to the maximum extent, thereby improving the detection sensitivity and overall accuracy, and ultimately ensuring the system's high-precision dynamic detection capability of weak magnetic components in materials. Magnetic detection sensors are small in size, highly integrated, and portable, making them convenient for on-site operation and integration into large instruments. Attached Figure Description

[0020] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings: Figure 1 This is a schematic diagram of the structure of the detection sensor according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the thin-film structure of the Hall device according to an embodiment of the present invention; Figure 3 This is a schematic diagram showing the positional relationship between the Hall device and the metal electrode in an embodiment of the present invention; Figure 4 This is a top view of the Hall device and flux amplifier according to an embodiment of the present invention; Figure 5 This is a schematic diagram of the main structure of the Hall device and flux amplifier according to an embodiment of the present invention; Figure 6 This is a poloidal Kerr effect curve of the detection chip in the short axis direction according to an embodiment of the present invention; Figure 7 This is a poloidal Kerr effect curve of the detection chip in the long axis direction according to an embodiment of the present invention; Figure 8 This is a schematic diagram of the structure of a bare Hall device with a flux concentrator and a preamplifier in Embodiment 4 of the present invention; Figure 9 This is a schematic diagram of the structure of the bare Hall device and the data acquisition board in Embodiment 1 of the present invention; Figure 10 The above is a sensitivity curve of the bare Hall device according to Embodiment 1 of the present invention. Figure 11 This is a noise curve of the bare Hall device according to Embodiment 1 of the present invention; Figure 12 This is a schematic diagram of the structure of the bare Hall device with a magnetic flux concentrator in Embodiment 2 of the present invention; Figure 13 This is a sensitivity curve of the bare Hall device with a flux concentrator in Embodiment 2 of the present invention; Figure 14 This is a schematic diagram of the structure of the Hall device bare device plus preamplifier in Embodiment 3 of the present invention; Figure 15 This is a sensitivity curve of the preamplifier in Embodiment 3 of the present invention at the 100 level. Figure 16 This is a noise curve of the preamplifier in Embodiment 3 of the present invention at the 100 level. Figure 17 This is a sensitivity curve of the preamplifier in Embodiment 3 of the present invention at the 500 level; Figure 18 This is a noise curve of the preamplifier in Embodiment 3 of the present invention at the 500 level; Figure 19 This is a sensitivity curve of the preamplifier in Embodiment 4 of the present invention at the 500 level; Figure 20 This is a sensitivity curve of the bare Hall device of Comparative Example 1 of the present invention. Figure 21 This is a sensitivity curve of the bare Hall device of Comparative Example 2 of the present invention.

[0021] In the diagram, 10 is the data acquisition board; 20 is the detection chip; 30 is the magnetic flux concentrator; 40 is the current source; 50 is the nanovoltmeter; 60 is the host computer; and 70 is the preamplifier. 21. Substrate; 22. Hall effect device; 23. Metal electrode; 31. Flux focusing plate; 221. Heavy metal 222, Magnetic thin film layer; 223, Heavy metal П layer. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0023] In the description of this invention, it should be understood that the terms "center", "lateral", "longitudinal", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0024] The terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first," "second," or "third" may explicitly or implicitly include one or more of that feature.

[0025] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0026] This embodiment provides a weak magnetic field detection sensor based on the planar Hall effect, such as... Figure 1 As shown, it includes a data acquisition board 10 and a detection chip 20 and a magnetic flux concentrator 30 disposed on the data acquisition board 10.

[0027] The data acquisition board 10 has a current input port and a voltage output port.

[0028] like Figures 2-3As shown, the detection chip 20 includes a substrate 21 and an elliptical Hall effect device 22 laid on the upper surface of the substrate 21. In this embodiment, a thermally oxidized silicon wafer is used as the substrate. The substrate 21 is placed flat on the upper surface of the data acquisition board 10. The Hall effect device 22 is provided with multiple metal electrodes 23, which are respectively connected to the current input port and the voltage output port. The current input port is used to input the current signal to the Hall effect device 22, and the voltage output port is used to output the Hall voltage signal of the Hall effect device 22.

[0029] like Figure 2 As shown, the Hall device 22 comprises heavy metals sequentially along a direction perpendicular to the substrate 21. Layer 221, magnetic thin film layer 222, heavy metal П layer 223, wherein, heavy metal The material of layer 221 is Ta, the material of heavy metal layer 223 is Pt, and the material of magnetic thin film layer 222 is FeNi.

[0030] Ta has extremely low surface roughness, which can be used as a seed layer to improve the growth quality of FeNi layers; the Ta layer has excellent surface smoothness and substrate adhesion. Deposited as a seed layer on the substrate, it can effectively modify the substrate surface, providing a uniform, dense, and low-roughness growth template. This significantly improves the crystallization quality of the subsequent FeNi ferromagnetic layer, promoting the formation of a more complete crystal structure with fewer defects.

[0031] Secondly, a high-quality FeNi layer directly enhances its intrinsic anisotropic magnetoresistance (AMR) effect. The AMR amplitude is closely related to the crystal integrity, electron mean free path, and scattering anisotropy of the ferromagnetic material. After optimized growth using a Ta seed layer, the crystal defects in the FeNi layer are reduced, and grain boundary scattering is decreased, thereby enhancing the AMR response amplitude and making the magnetoresistance signal more significant.

[0032] Therefore, the introduction of a Ta seed layer not only improves the structural quality and reliability of the multilayer film, but also directly enhances the magnetic transport properties of the FeNi layer, providing an important foundation for obtaining high-performance magnetoelectric devices.

[0033] Pt has good chemical stability and can be used as a protective layer to prevent the FeNi layer from oxidizing in air.

[0034] It should be noted that in the Ta / FeNi / Pt three-layer film structure, the synergistic effect of anisotropic magnetoresistance (AMR) and spin Hall magnetoresistance (SMR) can be used to achieve high-sensitivity weak magnetic field detection based on the planar Hall effect (PHE). The sensor principle is mainly based on the following mechanism: First, in this three-layer film system, the top Pt and bottom Ta layers both have strong spin-orbit coupling, and their spin Hall angles have opposite signs. When a current is passed along the film plane, the Pt and Ta layers generate spin currents in the vertical direction through the spin Hall effect, which are injected into the middle FeNi magnetic film layer. The FeNi layer, as the sensitive unit, has its magnetization direction modulated by an external magnetic field. Due to the SMR effect, the reflection and absorption efficiency of the interface spin current strongly depends on the magnetization direction of the FeNi layer, thus modulating the longitudinal resistance of the entire stack. Simultaneously, the AMR effect of the FeNi layer itself also directly contributes to the anisotropic change in resistance with magnetization direction. Crucially, SMR and AMR have the same angle dependence on magnetization direction; therefore, their signals are superimposed in phase, achieving synergistic enhancement. This enhanced magnetoresistive response ultimately manifests as a significantly increased planar Hall voltage. When a weak external magnetic field alters the magnetization direction of the FeNi layer, the PHE voltage changes with high sensitivity. By detecting this voltage signal, the strength and direction of the external magnetic field can be accurately inverted. This sensor structure fully utilizes the spin injection capability of the heavy metal layer and the magnetosensitive properties of the magnetic thin film layer. Through synergistic amplification of AMR and SMR, a high signal-to-noise ratio output signal can be obtained without complex magnetic biasing, providing an effective device solution for applications such as low-frequency weak magnetic field detection, biomagnetic sensing, and high-density magnetic storage readout.

[0035] Furthermore, anisotropic magnetoresistance (AMR) refers to the phenomenon where the resistance of a magnetic conductor changes with the angle between its internal magnetization direction and the current direction. The resistance is highest when the magnetization direction is parallel to the current and lowest when it is perpendicular to the current. Its physical mechanism primarily stems from the fact that the probability of electron scattering caused by spin-orbit coupling depends on the magnetization direction, thus leading to anisotropy in resistance. The AMR effect is particularly pronounced in magnetic metals and alloys (such as permalloy NiFe) and has been a crucial foundation for magnetic sensing technology since its discovery in the 19th century. AMR-based sensors possess advantages such as simple structure, high sensitivity, and fast response, and are widely used in fields such as magnetic field measurement, position detection, current sensing, and hard disk read / write heads.

[0036] Spin Hall magnetoresistance (SMR) is a magnetoresistance effect observed in heterojunctions of magnetic insulators / heavy metals (or strongly spin-orbit coupled materials). Its core physical mechanism stems from the synergistic effect of the spin Hall effect and the inverse spin Hall effect. When current passes through the heavy metal layer, due to the spin Hall effect, electrons undergo spin-dependent deflection due to spin-orbit coupling, generating a pure spin current perpendicular to the current direction. This spin current is injected into the adjacent magnetic insulator interface. The fate of the spin current (whether it is reflected, absorbed, or converted) strongly depends on the direction of magnetization in the magnetic insulator. The spin current, modulated by the magnetic thin film layer and returning to the heavy metal layer, is converted back into charge current or voltage signal through the inverse spin Hall effect, ultimately manifesting as a change in the overall device resistance with the magnetization direction. A key characteristic of SMR is that the magnitude of the SMR resistance depends on the angle between the magnetization direction and the spin current polarization direction at the heavy metal / magnetic insulator interface, typically satisfying the following condition: The relationship.

[0037] Therefore, although their physical origins are completely different—AMR originates from the anisotropic scattering within the magnetic thin film layer, while SMR originates from the generation, modulation, and conversion of interfacial spin current—in conductive magnetic metal / heavy metal systems, the SMR effect often coexists with anisotropic magnetoresistance (AMR). Both have the same angle dependence, thus the signals can be linearly superimposed (synergistically enhanced) to achieve a high-sensitivity magnetic sensor.

[0038] The planar Hall effect (PHE) is a unique transverse magnetoresistance phenomenon in ferromagnetic materials. Unlike the conventional Hall effect (where the magnetic field is perpendicular to the current), in PHE, both the magnetic field and the current lie in the same plane. When an applied magnetic field causes the magnetization direction of the material to deviate from the current direction, the resistance changes with the angle between the magnetization direction and the current due to the presence of anisotropic magnetoresistance (AMR). This anisotropy of resistance generates an observable transverse voltage in the direction perpendicular to the current; this voltage is called the planar Hall voltage, and its magnitude is typically [missing information - likely a value]. Proportional (where (This is the angle between the magnetization direction and the current).

[0039] In conductive magnetic metal / heavy metal heterojunction systems, the physical picture of the planar Hall effect becomes richer. Its signal amplitude is no longer solely determined by the AMR effect within the magnetic metal layer, but is simultaneously influenced by both AMR and spin Hall magnetoresistance (SMR) mechanisms, and these two mechanisms can synergistically enhance each other. 1. Contribution of AMR: As a fundamental mechanism, it originates directly from the anisotropy of electron scattering within the magnetic thin film layer (FeNi), and is the direct physical source of the planar Hall voltage.

[0040] 2. Modulation and Enhancement of SMR: In the presence of a heavy metal layer (Pt, Ta), a spin current generated by the spin Hall effect is injected into the magnetic thin film layer. The magnetization direction of the magnetic thin film layer, by influencing the reflection or absorption efficiency of this spin current at the interface, in turn modulates the charge-spin conversion process in the heavy metal layer. This SMR mechanism alters the longitudinal resistance of the entire heterojunction and effectively modulates the effective magnetic state or spin accumulation of the magnetic thin film layer, thereby indirectly but significantly affecting the response efficiency of AMR.

[0041] 3. Synergistic Enhancement Mechanism: AMR and SMR exhibit the same angular function dependence on the magnetization direction. This means that when the magnetization direction changes due to an applied magnetic field, the resistance changes generated by the two effects are in phase. Therefore, SMR not only contributes to the resistance change itself, but more importantly, it amplifies the effective magnetic response of the magnetic thin film layer through spin-current interface interaction, resulting in an overall enhancement of the planar Hall voltage signal based on AMR. This synergistic effect enables heterojunction-based planar Hall sensors to achieve sensitivity far exceeding that of single magnetic metal materials.

[0042] In summary, the planar Hall effect in magnetic metal / heavy metal heterostructures is the result of the combined effects of AMR (direct source) and SMR (interface modulation and enhancement). This synergy not only enriches the physical implications of spin transport but also provides a key principle for designing high-performance, high-sensitivity magnetic sensors.

[0043] A typical experimental phenomenon based on this principle is observed within the plane of a magnetic metal / heavy metal heterojunction. The direction of the current flowing through the Hall device is fixed, while the direction of the in-plane magnetic field is rotated to change the direction of the magnetic moment. At this point, a voltage signal related to the angle of the magnetic field can be measured on the two electrodes perpendicular to the current direction; this is the planar Hall voltage. For the magnetic metal / heavy metal heterojunction system, the amplitude of this voltage is contributed by both AMR and SMR, and they are synergistically enhanced due to their identical angle dependence, exhibiting a double-angle sine (sin2θ) characteristic. θ Dependency relationship. That is, the plane Hall voltage V PHE This can be expressed as: V PHE = R AMR+SMR ×I0×sin2 θ Among them, R AMR+SMR The magnetoresistance of the magnetic thin film layer after synergistic enhancement by AMR and SMR can be expressed as R. AMR+SMR =R / / - R ⊥ , where R / / R represents the resistance when the magnetic moment in the magnetic thin film is parallel to the direction of the current. ⊥ I0 represents the resistance when the magnetic moment in the magnetic thin film is perpendicular to the direction of the current, and I0 represents the magnitude of the current. θ The angle between the current direction and the magnetic moment direction is denoted by . Therefore, this unique magnetoresistive effect, formed by the synergistic enhancement of AMR and SMR, can significantly increase the planar Hall voltage. By improving the signal-to-noise ratio and intensity of the output signal, it ultimately achieves high-sensitivity detection of weak magnetic fields, which is one of the reasons for its ultra-high detection sensitivity. The elliptical Hall device exhibits anisotropy along its major axis, and its elliptical structure can be uniformly magnetized, generating a uniform demagnetizing field inside. This promotes the formation of an ideal single-domain structure in the magnet. When a weak external magnetic field exists, the rotation of the magnetic moment manifests as a coordinated change of all magnetic moments, completely eliminating the resistance caused by the pinning of domain walls in multi-domain materials. Since the response of the magnetic moment no longer needs to overcome the energy barrier of domain wall movement, the sensor's response capability to weak magnetic fields is greatly enhanced, which is the second reason for its ultra-high detection sensitivity.

[0044] like Figures 4-5 As shown, the flux concentrator 30 is also placed flat on the data acquisition board 10, and is located on the upper surface of the data acquisition board 10 along with the Hall device 22. The flux concentrator 30 includes flux concentrating plates 31 arranged on both sides of the Hall device 22 with the major axis of the Hall device 22 as the axis of symmetry. The flux concentrating plates 31 are isosceles trapezoidal structures. The extension line of the minor axis of the Hall device 22 passes through the midpoint of the upper and lower bases of the isosceles trapezoidal structure in sequence. That is to say, the upper base of the flux concentrating plate 31 is close to the minor axis of the Hall device 22, and the upper and lower bases of the flux concentrating plate 31 are parallel to the major axis of the Hall device 22. The flux concentrating plate 31 is used to directionally amplify the magnetic field in the direction of the minor axis of the Hall device 22.

[0045] Due to the low magnetic permeability of air, the flux concentrator 30 can effectively concentrate weak magnetic fields in space, enhancing the magnetic flux density at both ends of the sensor. Placing the flux concentrator 30 at both ends of the short axis of the Hall device 22 enables directional amplification of the magnetic field in the short axis direction. It is worth emphasizing that the introduction of the flux concentrator 30 does not increase additional detection noise, thereby further improving the sensitivity of the device without sacrificing the signal-to-noise ratio. This is the third reason for its ultra-high detection sensitivity.

[0046] The weak magnetic field detection sensor in this technical solution adopts an elliptical Hall device with shape anisotropy along the major axis. By placing the magnetic flux concentrator at both ends of the minor axis of the Hall device, the magnetic field in the minor axis direction can be amplified in a directional manner. This can effectively concentrate the weak magnetic field in space, enhance the magnetic flux density at both ends of the minor axis of the Hall device, and does not increase the detection noise. Without sacrificing the signal-to-noise ratio, the sensitivity of the detection sensor is further improved, achieving detection accuracy on the order of pT.

[0047] In some embodiments, such as Figure 3 As shown, the length of the major axis of the Hall device 22 is a and the length of the minor axis is b, with a length ratio of a:b of 6:1. This aspect ratio greatly enhances the Hall device 22's response to weak magnetic fields, enabling it to achieve ultra-high detection sensitivity and achieving the best balance between sensitivity and practicality.

[0048] A suitable ratio of major to minor axis lengths is crucial for balancing the orientation stability of the magnetic moment and the sensitivity of the magnetic field response. When the ratio is too large, an excessively strong demagnetizing field is generated, which excessively "locks" the magnetic moment along the major axis, weakening its ability to respond to weak magnetic fields along the minor axis and thus reducing detection sensitivity. Conversely, if the ratio is too small, the shape anisotropy equivalent field along the major axis will be significantly weakened, potentially disrupting the single-domain state that maintains high sensitivity and even causing the magnetic anisotropy along the major axis to disappear, making the sensor unable to effectively detect weak magnetic fields along the minor axis.

[0049] In some embodiments, heavy metals The thickness of layer 221Ta and heavy metal layer 223Pt is 5nm, and the thickness of magnetic thin film layer 222FeNi is 50nm. When the magnetic thin film layer FeNi is too thin, the in-plane uniaxial anisotropy is large, the disturbance of the magnetic moment by the weak magnetic field may be reduced, and the detection sensitivity will decrease. When the magnetic thin film layer is too thick, the out-of-plane anisotropy gradually increases, which is not conducive to the application of planar Hall effect.

[0050] In some embodiments, the flux focusing plate 31 is made of permalloy, which has high permeability and can efficiently focus and guide ambient magnetic field lines to the sensitive area, thereby amplifying the local magnetic field by tens of times, thus directly amplifying the output signal, while avoiding the introduction of additional circuit noise, thereby further improving the detection accuracy of the Hall device.

[0051] The magnetic flux concentrator 31 combines the anisotropy of the elliptical Hall effect device 22 along its major axis with the magnetic field enhancement mechanism to achieve directional enhancement of the magnetic field along the minor axis, without introducing additional circuit noise. When the magnetic flux concentrator is used alone, the sensitivity is increased to ≥2627 Ω / T, the noise remains unchanged at 11 nV / √Hz, and the accuracy reaches ≥0.4 nT / √Hz.

[0052] In some embodiments, the metal electrode 23 is a gold electrode with a thickness of 100 nm. The gold electrode has high conductivity, corrosion resistance, and thermal stability, as well as low contact resistance and low loss characteristics, and is widely used in high-performance devices.

[0053] In some embodiments, as heavy metals The Ta layer 221, the FeNi magnetic thin film layer 222, and the Pt heavy metal layer 223 are deposited on a thermally oxidized silicon wafer substrate 21 using a magnetron sputtering process to fabricate a Hall device 22; specifically: at a depth of less than 5 × 10⁻⁶... 5 In a vacuum environment of 0.6 Pa, argon gas is introduced as the sputtering gas at a flow rate of 15 sccm and a sputtering pressure of 0.6 Pa. Heavy metals are then grown sequentially using magnetron sputtering. Layer 221Ta, magnetic thin film layer 222FeNi, and heavy metal П layer 223Pt; the thin film is fabricated into an elliptical shape using photolithography and ion beam etching. This fabrication produces a multilayer thin film device with a uniform structure and clear edges, which can reduce 1 / f noise and thermal noise caused by material defects at the source.

[0054] A 100 nm thick gold film was grown on a heavy metal П-layer 223Pt by magnetron sputtering in a vacuum environment below 5 × 10⁵ Pa. The shape of the gold electrode was obtained by overlay process, and then the gold electrode was fabricated by lift-off process. The lift-off process is as follows: after sputtering the 100 nm gold film, the sample was immersed in acetone and sonicated. The gold electrode was deposited on the heavy metal П-layer 223 by lift-off process to form the detector chip 20. The detector chip 20 was annealed in a vacuum at 200°C for 1 hour to remove heavy metals. The crystallization of the Ta layer, the magnetic thin film layer 222FeNi, and the heavy metal П layer 223Pt releases interlayer stress and further enhances soft magnetic properties. If the annealing temperature is too low, it is insufficient to crystallize the thin film layers and cannot release the stress present during the growth process; if the temperature is too high, it will damage the film and cause oxidative denaturation.

[0055] It should be noted that thermal annealing improves the crystallinity of thin films because nanofilms form amorphous or defective structures during deposition. Thermal annealing allows atoms to rearrange and crystallize more completely, which is helpful for conductivity or magnetism, such as more uniform magnetic domain movement and reduced coercivity.

[0056] The annealed detector chip 20 exhibits excellent soft magnetic properties, such as... Figures 6-7As shown, by testing the hysteresis loop of the sample using a magneto-optical Kerr microscope, the coercivity and anisotropic field of the detector chip 20 in the plane can be obtained. It can be seen from the figure that for the annealed sample, the results show extremely small coercivity (2 Oe) and anisotropic field (4 Oe).

[0057] Meanwhile, thermal annealing can also optimize the interface; the interface state between multilayer films is crucial, especially the diffusion and mixing between layers. Heat treatment can promote atomic diffusion, form a clearer interface, resulting in higher spin transparency, reduced spin memory loss, and improved SMR.

[0058] Thermal annealing can improve its magnetic properties. For soft magnetic materials such as FeNi, grain growth can reduce the number of grain boundaries that hinder the movement of magnetic domain walls, thereby reducing coercivity, increasing permeability, and reducing hysteresis loss. A more complete lattice is also conducive to improving saturation magnetization and enhancing AMR.

[0059] Thermal annealing can also release the internal stress of the film during the growth process. Releasing stress can make the film performance more stable and closer to the intrinsic value of the material. Stress will significantly affect the magnetostriction and magnetic anisotropy of FeNi. Stress release helps to obtain softer magnetic properties (low coercivity).

[0060] On the other hand, in some embodiments, a weak magnetic detection system is also provided, such as... Figure 8 As shown, the device includes a current source 40, the aforementioned detection sensor, and a nanovoltmeter 50. The current source 40 is connected to the current input port of the detection sensor to provide current to the sensor. The nanovoltmeter 50 is connected to the voltage output port of the detection sensor to collect the Hall voltage signal generated by the sensor. The nanovoltmeter 50 is also connected to a host computer 60, which reads the voltage data detected by the nanovoltmeter 50 and analyzes and processes the voltage data to obtain magnetic field strength data.

[0061] In some embodiments, a preamplifier 70 is provided between the nanovoltmeter 50 and the voltage output port. That is, the preamplifier 70 is connected in series in the detection circuit to perform low-noise primary amplification of the microvolt-level Hall voltage generated by the detection sensor. The nanovoltmeter 50 collects the amplified Hall voltage data and sends it to the host computer to further improve the detection accuracy.

[0062] The preamplifier 70 significantly enhances the overall response capability of the detection sensor to external magnetic fields. At the same time, thanks to the excellent low noise characteristics of the preamplifier 70, it suppresses the introduction of additional noise to the maximum extent while amplifying the effective signal, thereby simultaneously improving detection sensitivity and overall accuracy.

[0063] In some embodiments, the preamplifier 70 has two amplification levels: 100 levels and 500 levels. It improves detection accuracy by directly amplifying the electrical signal output by the sensor. When the sensor is in its bare device state, its detection sensitivity is ≥257Ω / T, noise is ≤9 nV / √Hz at 1Hz, and accuracy is ≥2.16 nT / √Hz. After connecting the 100-level preamplifier, the sensitivity is increased to ≥21359 Ω / T, noise is ≤84 nV / √Hz, and accuracy is improved to ≥81 pT / √Hz. When using the 500-level preamplifier, the sensitivity further reaches ≥124917 Ω / T, noise is ≤172 nV / √Hz, and accuracy is improved to ≥21 pT / √Hz.

[0064] On the other hand, in some embodiments, an application of the aforementioned weak magnetic detection sensor in the magnetic detection of concrete and its raw materials is also provided; the detection sensor is encapsulated and pre-embedded in concrete, which can quantitatively provide the remanent magnetism of concrete and monitor changes in the remanent magnetism of concrete; or it can be placed in concrete raw materials such as sand, gravel, and cement to quantitatively provide the remanent magnetism of the raw materials; the sensor is extremely small in size, has extremely high detection accuracy (pT level) and integration, and the device size is extremely small (15cm*15cm), which is convenient for on-site operation and integration with large instruments, and can meet the quantitative testing of the magnitude of weak magnetic remanent magnetism in concrete.

[0065] Example 1 I. Fabrication of the detector chip 20: 1) Cleaning the substrate: Using Si / SiO2 as the substrate 21 of the detector chip, the Si / SiO2 substrate was immersed in acetone and ultrasonically oscillated once, and then ultrasonically oscillated once in anhydrous ethanol. Each oscillation time was 20 min, and then it was stored in deionized water. 2) Heavy metals are deposited on the substrate obtained after cleaning in step 1). The layers consist of a Ta layer, a FeNi magnetic thin film layer 222, and a Pt heavy metal П layer 223; magnetron radio frequency sputtering is used to achieve a sputtering process with a density below 5 × 10⁻⁶. 5 In a vacuum environment of Pa, argon gas is introduced as the sputtering gas at a flow rate of 15 sccm and a sputtering pressure of 0.6 Pa to grow a Hall device thin film. The Hall device 22 structure is Ta 5nm / FeNi 50nm / Pt 5nm, as shown below. Figure 2 As shown; 3) Using photolithography, the core part of the Hall device is fabricated on the Hall device film: AZ601 photoresist is spin-coated onto the surface of the Hall device film at a speed of 4000 r / min, and then pre-baked on a 120℃ heating stage for 120s; after baking, an elliptical pattern is exposed onto the photoresist using a laser direct writing instrument, and then developed for 1 min. After development, it is rinsed with deionized water. 4) Using ion beam etching technology, the developed sample is placed in an ion beam etching instrument and etched with an ion beam to remove excess film, leaving an elliptical Hall device 22 part. Then, it is ultrasonically washed in acetone to remove the photoresist on the surface. At this time, the Hall device is fabricated. The length a of the major axis of the Hall device 22 is 1200μm and the width b is 200μm. 5) Secondary photolithography: Overlaying is performed around the Hall device. AZ601 photoresist is spin-coated onto the surface of the multilayer Hall device thin film at a speed of 4000 r / min. Then, pre-baking is performed on a 120℃ heating stage for 120s. After baking, the pattern is exposed onto the photoresist using a laser direct writing instrument. After exposure, development is performed for 1 min. After development, the image is rinsed with deionized water. 6) Gold electrodes were sputtered using magnetron sputtering to obtain the detector chip. Ta was sputtered for 2 min at 20W DC power to a thickness of 5 nm, followed by Au sputtering for 15 min at 50W to a thickness of 100 nm. After sputtering, a lift-off process was used, sequentially immersing the chip in acetone, anhydrous ethanol, and deionized water. A stripping technique was then used to remove the photoresist and excess Ta and Au, resulting in four patterned gold electrodes. Figure 3 As shown; 7) The prepared detector chip 20 is thermally annealed to improve the crystallinity of the magnetic nanofilm. The detector chip 20 sample to be annealed is placed in a vacuum annealing furnace, the sample to be annealed is evacuated, heated to 200°C and held for 1 hour, and then taken out after naturally cooling to room temperature.

[0066] 2. Place the detector chip 20 on the data acquisition board 10. In this embodiment, the data acquisition board 10 has two circuit input ports and two voltage output ports, which are respectively connected to the four gold electrodes of the detector chip 20. Figure 9 As shown; The sensitivity and noise of the detector chip 20 are key factors affecting its performance. This embodiment evaluates the sensitivity and noise of the detector chip 20, which is a bare device, by scanning a magnetic field near the zero magnetic field range. Figure 10As shown, by fitting the linear relationship between the Hall voltage and the external magnetic field, the sensitivity of the detector chip 20 in Example 1 is obtained as 233 Ω / T; the nanovoltmeter 50 is connected to the two voltage output ports on the data acquisition board 10 to acquire the Hall voltage, and the current source 40 is connected to the two current input ports on the data acquisition board 10 to input the current, as shown. Figure 11 As shown, the noise of the detection chip 20 is 11 nV / √Hz at @1Hz, and the accuracy is 2.38 nT / √Hz.

[0067] Example 2 A flux concentrator 30 is installed on the data acquisition board of Example 1; as shown Figure 12 As shown, isosceles trapezoidal magnetic flux concentrators 31 are respectively installed on both sides of the short axis of the Hall device 22 in Embodiment 1. The magnetic flux concentrators 31 are permalloy sheets with high magnetic permeability; due to the magnetic flux concentrators 30 concentrating the magnetic field in the short axis direction of the Hall device 22, such as Figure 13 As shown, the sensitivity of the detection chip 20 is increased to ≥ 2627 Ω / T at this time; since the magnetic flux concentrator 30 is attached to both ends of the short axis of the detection chip 20 and is not connected to the circuit, no additional noise will be generated. Therefore, the noise @1Hz ≤ 11 nV / √Hz remains unchanged, and the accuracy is improved to ≥ 0.4 nT / √Hz.

[0068] Example 3 Remove the flux concentrator 30 from Example 2 and connect it to the preamplifier 70, as follows: Figure 14 As shown, the sensitivity and noise are measured; the preamplifier 70 has two settings: 100 and 500. When the 100 setting is connected, as shown... Figure 15 As shown, its sensitivity is improved to ≥ 20087 Ω / T, such as Figure 16 As shown, the noise level at 1Hz ≤ 98 nV / √Hz, and the accuracy ≥ 97 pT / √Hz; when connected to the 500 setting, as... Figure 17 As shown, its sensitivity is improved to ≥ 114441 Ω / T, as Figure 18 As shown, the noise at this time is ≤ 191 nV / √Hz at 1Hz, and the accuracy is ≥ 33 pT / √Hz.

[0069] Example 4 When the flux concentrator 30 and the preamplifier 70 are used simultaneously, such as Figure 8 As shown, in this embodiment, after connecting the flux concentrator 30 and the 500-level switch of the preamplifier 70, as... Figure 19As shown, its detection sensitivity is ≥ 1445720 Ω / T, and its noise is the same as that of the preamplifier 70 in Example 3 at the 500 level, which is @1Hz ≤ 191 nV / √Hz. Its accuracy is ≥ 2.6 pT / √Hz, which can realize the detection of weak magnetic fields on the pT level.

[0070] Comparative Example 1 The difference from Example 1 is that the length a of the major axis of Hall device 22 is 800μm, the width b is 200μm, and the aspect ratio is 4:1.

[0071] like Figure 20 As shown, the bare device was tested and found to have a sensitivity of 98 Ω / T, a noise level of 11 nV / √Hz at 1Hz, and an accuracy of 6.09 nT / √Hz. When the ratio of the major axis to the minor axis is too large, although the shape anisotropy effect is stronger, the excessively strong demagnetizing field will bind the magnetic moment too tightly in the direction of the major axis, which will weaken the response to the weak magnetic field in the direction of the minor axis and lead to a decrease in sensitivity.

[0072] Comparative Example 2 The difference from Example 1 is that the length a of the major axis of Hall device 22 is 1600μm, the width b is 200μm, and the aspect ratio is 8:1.

[0073] like Figure 21 As shown, the bare device was tested and found to have a sensitivity of 171 Ω / T, a noise level of 11 nV / √Hz, and an accuracy of 3.24 nT / √Hz. If the ratio of the major axis to the minor axis is too small, the shape anisotropy equivalent field along the major axis will be significantly weakened. This may not only disrupt the single-domain states required to maintain high sensitivity, but could even lead to the complete disappearance of magnetic anisotropy along the major axis, causing the sensor to lose its basic function of detecting weak magnetic fields along the minor axis.

[0074] Choosing an appropriate aspect ratio is crucial for balancing the orientation stability of the magnetic moment and the sensitivity of the magnetic field response. Experiments have verified that an elliptical structure with a major axis to minor axis ratio of 6:1 can achieve the best detection accuracy for bare devices.

[0075] Based on the above technical solution, the weak magnetic detection sensor of the present invention utilizes the high charge-spin conversion efficiency of Ta and Pt and their opposite spin Hall angles, placing them on the upper and lower sides of a magnetic thin film layer respectively, and injecting spin currents with the same spin polarization direction into the magnetic thin film layer, which can generate significant spin currents in the three-layer film structure; this spin current can induce a large spin Hall magnetoresistance, and its magnetic field angle dependence is consistent with the anisotropic magnetoresistance in the magnetic thin film layer. Therefore, Ta and Pt can synergistically enhance the high-sensitivity magnetic field response. By using an elliptical Hall device and placing the magnetic flux concentrator at both ends of the short axis of the Hall device, the magnetic field in the short axis direction can be amplified in a directional manner, enhancing the magnetic flux density at both ends of the short axis of the Hall device without increasing the detection noise. This further improves the sensitivity of the detection sensor without sacrificing the signal-to-noise ratio, achieving a detection accuracy on the order of pT. While amplifying the effective signal, the preamplifier can suppress the introduction of additional noise to the maximum extent, thereby improving the detection sensitivity and overall accuracy, and ultimately ensuring the system's high-precision dynamic detection capability of weak magnetic components in materials. Magnetic detection sensors are small in size, highly integrated, and portable, making them convenient for on-site operation and integration into large instruments.

[0076] Finally, it should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0077] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A weak magnetic field detection sensor based on the planar Hall effect, characterized in that, include: The data acquisition board has a current input port and a voltage output port; The detection chip includes a substrate disposed on the data acquisition board and an elliptical Hall effect device laid on the upper surface of the substrate; The Hall device is provided with a plurality of metal electrodes, which are respectively connected to the current input port and the voltage output port; A magnetic flux concentrator is disposed on the data acquisition board. The magnetic flux concentrator includes magnetic flux concentrating plates disposed on both sides of the Hall device with the major axis of the Hall device as the axis of symmetry. The magnetic flux concentrating plates are isosceles trapezoidal structures. The extension line of the minor axis of the Hall device passes through the midpoint of the upper and lower bases of the isosceles trapezoidal structure in sequence. The magnetic flux concentrating plates are used to directionally amplify the magnetic field in the direction of the minor axis of the Hall device.

2. The weak magnetic field detection sensor based on the planar Hall effect according to claim 1, characterized in that, The ratio of the length of the major axis to the length of the minor axis of the Hall device is 6:

1.

3. The weak magnetic field detection sensor based on the planar Hall effect according to claim 1, characterized in that, The Hall device comprises heavy metals sequentially along a direction perpendicular to the substrate. Layer, magnetic thin film layer, heavy metal П layer, wherein the heavy metal The layer material is Ta, the heavy metal П layer material is Pt, and the magnetic thin film layer is FeNi.

4. The weak magnetic field detection sensor based on the planar Hall effect according to claim 1, characterized in that, The heavy metal The thickness of the layer and the heavy metal П layer is 5 nm, and the thickness of the magnetic thin film layer is 50 nm.

5. The weak magnetic field detection sensor based on the planar Hall effect according to claim 1, characterized in that, The flux-collecting sheet is made of permalloy.

6. The weak magnetic field detection sensor based on the planar Hall effect according to claim 1, characterized in that, The metal electrode is a gold electrode.

7. The weak magnetic field detection sensor based on the planar Hall effect according to claim 3, characterized in that, The heavy metal The Hall device is fabricated by depositing the magnetic thin film layer, the heavy metal Π layer, and the magnetic thin film layer onto the substrate using a magnetron sputtering process. A gold thin film is grown on the protective layer by magnetron sputtering, and a gold electrode is fabricated using a lift-off process to make the detector chip. The probe chip was annealed in a vacuum at 200°C for 1 hour.

8. A weak magnetic field detection system, characterized in that, The device includes a current source, a nanovoltmeter, a host computer, and a detection sensor as described in any one of claims 1-7; wherein the current source is connected to the current input port of the detection sensor to provide current to the detection sensor; the nanovoltmeter is connected to the voltage output port of the detection sensor to collect the Hall voltage signal generated by the detection sensor; the host computer is connected to the nanovoltmeter, and the host computer reads the voltage data detected by the nanovoltmeter and analyzes and processes the voltage data to obtain magnetic field strength data.

9. The weak magnetic field detection system according to claim 8, characterized in that, A preamplifier is provided between the nanovoltmeter and the voltage output port. The preamplifier amplifies the Hall voltage generated by the detection sensor, and the nanovoltmeter collects the amplified Hall voltage data.

10. The application of the detection sensor according to any one of claims 1-7 in the magnetic detection of concrete and its raw materials.

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