A gain resonant cavity weak magnetic sub-mode detection device based on an external feedback loop and a working method thereof

Abstract

This invention relates to a gain resonant cavity weak magneton mode detection device and its operating method based on an external feedback loop, comprising: a cavity magneton system, an external feedback loop, and a signal readout system; the cavity magneton system includes a resonant cavity and magnetic materials; the external feedback loop includes a low-noise amplifier, a directional coupler, an adjustable phase shifter, and a coaxial transmission line, forming a closed-loop structure with the input and output ports of the resonant cavity. By adjusting the operating voltage of the low-noise amplifier, the gain is controlled, thereby achieving dynamic regulation of the resonant cavity characteristics and overcoming the loss limitations of passive resonant cavities; the signal readout system utilizes various devices with microwave signal analysis capabilities. This invention, by constructing a gain resonant cavity with adjustable gain, achieves precise control of the resonant cavity system dissipation rate, thereby effectively reducing the resonant linewidth and improving spectral resolution.

Description

Technical Field

[0001] This invention relates to a gain resonant cavity weak magneton mode detection device based on an external feedback loop and its working method, belonging to the field of magnetic field detection technology. Background Technology

[0002] In recent years, two-dimensional van der Waals (vdW) magnetic materials have attracted widespread attention in spintronics, microwave devices, and quantum information processing due to their atomic-level thickness, tunable interlayer coupling, and good compatibility with heterostructures. Magnetons, as collective spin excitations in these materials, possess characteristics such as low transmission loss and long coherence time, and are considered important carriers for realizing low-power information transmission and magnetic signal processing. In two-dimensional vdW magnets, magnetons not only provide a new physical platform for studying low-dimensional magnetism and magnetization dynamics, but also lay the foundation for the development of novel magnetoelectronic devices. However, due to the generally small size and weak magnetic moment of two-dimensional magnets, and the fact that their magneton modes are mostly distributed in the microwave frequency band with low signal intensity, traditional ferromagnetic resonance and electrical detection methods (such as spin pumping and spin rectification) are significantly limited in terms of detection sensitivity and spectral line resolution. Especially under low-temperature conditions, different magneton modes may exhibit similar frequencies and large differences in damping, and some weak magneton modes are easily masked by the dominant resonance peak, making direct observation difficult.

[0003] To improve magnetic particle detection capabilities, existing technologies typically employ microwave resonant cavities coupled with magnetic particles to construct cavity magnetic particle systems. Utilizing the localization and enhancement of the microwave field by the resonant cavity can effectively improve the measurability of magnetic particle signals and achieve indirect readout of magnetic particle modes through a strong coupling mechanism. However, existing research has also pointed out that passive resonant cavities are limited in practical operation by intrinsic losses and linewidth issues caused by mode hybridization. When magnetic particle mode damping is strong or significant spectral line overlap occurs after coupling with cavity modes, the system's spectral resolution will significantly decrease. For ultra-weak magnetic particle signals, simply improving the quality factor of the passive cavity cannot fundamentally solve the problems of spectral line broadening and weak magnetic particle mode masking. Therefore, there is an urgent need to develop a detection device capable of operating at low temperatures and improving the resonant cavity response through the introduction of controllable gain, in order to enhance the identification capability of weak magnetic particle modes and achieve high-sensitivity, high-resolution detection of multiple magnetic particle modes in two-dimensional vdW magnets. Summary of the Invention

[0004] To address the limitations of existing weak magneton mode detection techniques, such as low signal intensity, limited spectral resolution, and the masking of weak magneton modes by dominant resonance peaks, this invention proposes and develops a highly sensitive weak magneton mode detection technique that can operate at low temperatures. This technique utilizes an active resonant cavity system with an external feedback loop to introduce gain, enabling precise control of the system's dissipation rate, thereby effectively reducing the resonance linewidth and improving spectral resolution. The main technical problem this invention aims to solve is: how to achieve stable construction and gain control of the gain resonant cavity at low temperatures, improving the system's sensitivity and resolution for low-damped, weak-signal magneton modes, while simultaneously maintaining stability and controllability under multimode coupling conditions.

[0005] The present invention also provides a method for operating the above-mentioned gain resonant cavity weak magneton mode detection device based on an external feedback loop.

[0006] Terminology Explanation: Room temperature usually refers to a temperature of 25 degrees Celsius or 300 Kelvin.

[0007] The technical solution of this invention is as follows: A gain resonant cavity weak magneton mode detection device based on an external feedback loop, comprising: Cavity magnetic subsystem, external feedback loop and signal readout system; The cavity magnetosystem includes a resonant cavity and a magnetic material. The resonant cavity is any one of a complementary open-loop resonant cavity, an open-loop resonant cavity, a microstrip cross resonant cavity, a Fabry-Perot resonant cavity, and a dielectric resonant cavity. The magnetic material is a material that generates magnetic resonance under microwave driving. The external feedback loop includes a low-noise amplifier, a directional coupler, an adjustable phase shifter, and a coaxial transmission line. The external feedback loop forms a closed-loop structure with the input and output ports of the resonant cavity. By adjusting the operating voltage of the low-noise amplifier to control the gain, the dynamic control of the resonant cavity characteristics can be achieved, thereby overcoming the loss limitation of the passive resonant cavity. The signal readout system uses a variety of devices with microwave signal analysis capabilities.

[0008] More preferably, the signal readout system is a vector network analyzer, a spectrum analyzer, or an oscilloscope.

[0009] More preferably, the directional coupler is replaced by a circulator or a power divider.

[0010] More preferably, the resonant cavity is a planar microwave resonant cavity based on a coplanar waveguide structure. In the central region of the resonant cavity, the current density is locally increased by narrowing the signal line width, so that the microwave magnetic field is locally enhanced at the signal line and the gap between the signal line and the ground line. The magnetic material is a two-dimensional van der Waals antiferromagnetic material, chromium chloride. The magnetic material is placed in the form of a thin sheet above the locally enhanced microwave magnetic field distribution area of ​​the resonant cavity signal line to achieve efficient magnetic excitation and coupling. An external static magnetic field is applied along the direction of the resonant cavity signal line to precisely control the resonance conditions of the magnetic mode. The resonant cavity is connected to a low-noise amplifier via two directional couplers, forming a closed external feedback loop. This external feedback loop is placed at room temperature and continuously provides adjustable gain to the resonant cavity in a low-temperature environment. By adjusting the operating voltage of the low-noise amplifier, partial or complete compensation of the cavity loss can be achieved, enabling the detection device to controllably switch between a high-quality factor state and a self-sustaining state, thereby significantly changing the equivalent linewidth of the resonant cavity and its response characteristics to magnetic signals. In addition, the detection device is connected to an external vector network analyzer as a detection unit, which inputs a weak detection signal through the coupling port of the directional coupler and collects the transmission parameter S. 21 It is used to characterize the spectral response of the resonant cavity-magnetic ion coupling system; by measuring and analyzing the transmission spectrum under different external magnetic field conditions and different operating states, it can achieve highly sensitive detection and accurate resolution of multiple magnetic ion modes.

[0011] More preferably, in the central region of the resonant cavity, by narrowing the width of the signal line from 1.14 mm to 0.4 mm, the local current density is increased by 2-3 times, thereby increasing the magnetic field energy density of the microwave magnetic field in the signal line and the gap between the signal line and the ground line by 5-6 times.

[0012] The operation of the aforementioned gain resonant cavity weak magneton mode detection device based on an external feedback loop includes: Step 1: Detection device construction and operating condition setting: Place the magnetic material at the narrowing point of the signal line in the central region of the resonant cavity signal line to fully couple the magnetic material with the microwave magnetic field inside the resonant cavity; at the same time, apply an external static magnetic field along the direction of the resonant cavity signal line to ensure that the resonant frequency of the magnon mode in the magnetic material is within the frequency range of the vector network analyzer under the control of the external static magnetic field, and operate in an environment below the magnetic ordering temperature of the magnetic material, so as to control the resonance condition of the magnon mode and ensure measurement stability; Step 2: Establishment and State Control of Active Resonant Cavity: A closed external feedback loop is constructed through two directional couplers and a low-noise amplifier to provide adjustable gain for the resonant cavity; the low-noise amplifier is supplied with operating voltage by a voltage source, and adjusting the operating voltage of the low-noise amplifier changes the amplifier's amplification factor, realizing incomplete and complete compensation of the gain for the cavity loss, so that the resonant cavity switches between a high-quality factor state and a self-sustaining state. The cavity in the self-sustaining state is a resonant cavity that spontaneously radiates microwave signals outward. Step 3: Magneton Excitation and Signal Enhancement Process: A weak microwave signal with a power below -40dB is input to the detection device using a vector network analyzer to form an enhanced microwave magnetic field in the resonant cavity, which excites the magneton mode in the magnetic material; the coupling system includes the resonant cavity and the magnetic material, so that the weak magneton mode can be observed; Step 4: Signal Detection and Pattern Analysis The first port of the vector network analyzer inputs microwaves into the detection device, and the second port of the vector network analyzer receives the transmitted microwaves after some of the microwave energy has been absorbed by the detection device. The ratio of the power of the transmitted microwaves to the power of the output microwaves is the transmission parameter S. 21 ; Under a fixed external magnetic field, the transmission parameter S 21 The change in microwave frequency is plotted as a transmission spectral line. By analyzing the frequency shift and linewidth information of the resonance peaks in the transmission spectra measured under different magnetic fields, the characteristics of the coupling mode of the coupled system as a function of the magnetic field are obtained. Based on the dynamic equations of the resonant cavity and magnon coupling system, the resonance characteristics and coupling behavior of different magnon modes are extracted.

[0013] According to a preferred embodiment of the present invention, in step 2, adjusting the operating voltage of the low-noise amplifier to change the amplifier's amplification factor means that the low-noise amplifier's turn-on voltage is 3.93V and its rated operating voltage is 8V; within the operating voltage adjustment range of 3.93V to 8V, the device gain is increased from 13.2dB to 26.6dB.

[0014] According to a preferred embodiment of the present invention, step 4 involves analyzing the frequency shift and linewidth information of the resonance peaks in the transmission spectra measured under different magnetic fields to obtain the characteristics of the coupling mode of the coupled system changing with the magnetic field; this includes: performing Lorentz fitting on the transmission spectra to extract the evolution law of the resonance frequency and the full width at half maximum (FWHM) of the resonance peak with the applied magnetic field; based on this evolution law, further analyzing the coupling strength, dispersion relation, and linewidth modulation characteristics of the photon-magneton coupling system, thereby accurately characterizing the dynamic evolution behavior of the intrinsic modes of the coupled system with the magnetic field.

[0015] The beneficial effects of this invention are as follows: This invention proposes a gain resonant cavity weak magneton mode detection device based on an external feedback loop. Compared with existing technologies, this invention achieves high-sensitivity detection of weak magneton signals by introducing an external feedback gain mechanism to construct a gain resonant cavity, significantly improving the observability and identifiability of complex magneton modes in two-dimensional magnetic materials. Specifically, this invention has the following beneficial effects: 1. Effectively suppressing spectral line broadening and improving spectral resolution: In passive cavities, the photon-magneton hybridization effect usually introduces significant linewidth broadening, leading to the masking of weak magneton modes. This invention utilizes a gain compensation mechanism to significantly narrow the equivalent linewidth of the resonant cavity, even achieving extremely narrow spectral lines (on the order of kHz) in a self-sustaining state, fundamentally improving the system's spectral resolution and thus achieving fine resolution of magneton modes.

[0016] 2. It possesses a highly adjustable working mechanism: By adjusting the amplifier gain (such as the bias voltage) in the feedback loop, the system can flexibly control the transition from the high-quality factor state to the self-sustaining state, achieving continuous adjustment of the cavity mode linewidth, gain intensity, and coupling state. This controllability enables the device to adapt to the detection requirements of different material systems and different signal strength ranges.

[0017] 3. High-precision measurement suitable for low-temperature environments: The gain resonant cavity structure of this invention can operate stably under low-temperature conditions, making it suitable for studying the magneton dynamics of two-dimensional vdW magnets near the low-temperature phase transition. Weak magneton modes are more pronounced at low temperatures, but traditional methods struggle to distinguish them. This invention, however, maintains high sensitivity and high resolution under these conditions, expanding the boundaries of measurement capabilities.

[0018] 4. Simple structure and easy integration and expansion: The present invention adopts a structural design based on planar coplanar waveguide and external feedback circuit. The overall structure is compact and the implementation is relatively simple. It is easy to integrate with other microwave circuits, spintronic devices or quantum devices and has good engineering application prospects.

[0019] 5. Expanding the application scenarios of two-dimensional magnetic material devices: This invention provides a general technical means for high-precision detection of magnetic modes in two-dimensional vdW magnets, which can promote its application in fields such as spintronics, microwave communication and quantum information processing, and provide key technical support for the development of new low-power magnetic information devices. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a detection device for a gain resonant cavity-CrCl3 coupling system based on an external feedback loop.

[0021] Figure 2The transmission spectra of the high-quality factor state and self-excited oscillation state resonator achieved under voltage regulation, as well as the transmission spectra of the CrCl3 magnon mode coupled with the active resonator at 2K temperature, are shown as variations with the magnetic field. Detailed Implementation

[0022] The present invention will be further defined below with reference to the accompanying drawings and embodiments, but is not limited thereto. Example 1

[0023] A gain resonant cavity weak magneton mode detection device based on an external feedback loop, comprising: Cavity magnetic subsystem, external feedback loop and signal readout system; The cavity magnetosystem includes a resonant cavity and a magnetic material. The resonant cavity is any one of a complementary split-ring resonator, a split-ring resonator, a microstrip-cross-junction cavity, a Fabry-Perot-like cavity, and a dielectric resonator. The magnetic material is a material that generates magnetic resonance under microwave drive. The external feedback loop includes a low-noise amplifier, a directional coupler, an adjustable phase shifter, and a coaxial transmission line. The external feedback loop forms a closed-loop structure with the input and output ports of the resonant cavity. By adjusting the operating voltage of the low-noise amplifier to control the gain, the dynamic control of the resonant cavity characteristics can be achieved, thereby overcoming the loss limitation of the passive resonant cavity. The signal readout system uses a variety of devices with microwave signal analysis capabilities. Example 2

[0024] The difference between the gain resonant cavity weak magneton mode detection device based on an external feedback loop described in Embodiment 1 and the device described in Embodiment 1 is as follows: The signal readout system is a vector network analyzer, spectrum analyzer, or oscilloscope.

[0025] The directional coupler is replaced with a circulator or power divider.

[0026] A feasible configuration of the present invention is as follows: Figure 1As shown, the resonant cavity is a planar microwave resonant cavity based on a coplanar waveguide structure. In the central region of the resonant cavity, the current density is locally increased by narrowing the signal line width, which locally enhances the microwave magnetic field at the signal line and the gap between the signal line and the ground line, thereby significantly improving the excitation efficiency of the magnetic sample. The magnetic material is a two-dimensional van der Waals antiferromagnetic material, chromium chloride (CrCl3). The magnetic material is placed in the form of a thin sheet above the locally enhanced microwave magnetic field distribution region of the resonant cavity signal line to achieve efficient magnetic excitation and coupling. An external static magnetic field is applied along the direction of the resonant cavity signal line to precisely control the resonance conditions of the magnetic mode. In terms of circuit configuration, the resonant cavity is connected to a low-noise amplifier through two directional couplers, forming a closed external feedback loop. This external feedback loop is placed in a room temperature environment and can continuously provide adjustable gain to the resonant cavity in a low-temperature environment. By adjusting the operating voltage of the low-noise amplifier, partial or complete compensation of the cavity loss can be achieved, enabling the detection device to controllably switch between a high-quality factor state and a self-sustaining state, thereby significantly changing the equivalent linewidth of the resonant cavity and its response characteristics to magnetic signals. In addition, the detection device is connected to an external vector network analyzer as a detection unit, which inputs a weak detection signal through the coupling port of the directional coupler and collects the transmission parameter S. 21 It is used to characterize the spectral response of the resonant cavity-magnetic ion coupling system; by measuring and analyzing the transmission spectrum under different external magnetic field conditions and different operating states, it can achieve highly sensitive detection and accurate resolution of multiple magnetic ion modes. Example 3

[0027] The difference between the gain resonant cavity weak magneton mode detection device based on an external feedback loop described in Embodiment 2 and the one described in Embodiment 2 is as follows: In the central region of the resonant cavity, by narrowing the width of the signal line from 1.14 mm to 0.4 mm, the local current density is increased by 2-3 times, which in turn increases the magnetic field energy density of the microwave magnetic field in the signal line and the gap between the signal line and the ground line by 5-6 times. Example 4

[0028] The difference between the gain resonant cavity weak magneton mode detection device based on an external feedback loop described in Embodiment 2 and the one described in Embodiment 2 is as follows: The 2.85-fold increase in local current density resulted in a 5.7-fold increase in the magnetic field energy density of the microwave magnetic field at the signal line and the gap between the signal line and the ground line. Theoretically, the higher the local current density, the better the detection effect. Example 5

[0029] The operation process of the gain resonant cavity weak magneton mode detection device based on an external feedback loop as described in any of Examples 1-4 includes: Step 1: Detection device construction and operating condition setting: Place the magnetic material at the narrowing point of the signal line in the central region of the resonant cavity signal line to fully couple the magnetic material with the microwave magnetic field inside the resonant cavity; at the same time, apply an external static magnetic field along the direction of the resonant cavity signal line to ensure that the resonant frequency of the magnon mode in the magnetic material is within the frequency range of the vector network analyzer under the control of the external static magnetic field, and operate in an environment below the magnetic ordering temperature of the magnetic material (for example, the antiferromagnetic ordering temperature of CrCl3 is about 14K) to control the resonance conditions of the magnon mode and ensure measurement stability; Step 2: Establishment and State Control of the Active Resonant Cavity: A closed external feedback loop is constructed using two directional couplers and a low-noise amplifier to provide adjustable gain for the resonant cavity. The low-noise amplifier is supplied with operating voltage by a voltage source. Adjusting the operating voltage of the low-noise amplifier changes the amplifier's amplification factor, achieving incomplete and complete compensation of the gain for intracavity losses, thus enabling the resonant cavity to operate in a high-quality factor state (e.g., ...). Figure 2 (as shown in (a)) and self-sustaining state (as shown in (a)) Figure 2 The system switches between the two types of resonant cavities (as shown in (b)). The high-quality factor cavity is a low-dissipation resonant cavity. When the applied voltage is 4.27V, the dissipation rate of the high-quality factor cavity can reach 4.8MHz. The self-sustaining cavity is a resonant cavity that spontaneously radiates microwave signals outward. This significantly compresses the equivalent linewidth and enhances the system's response to weak signals.

[0030] Step 3: Magneton Excitation and Signal Enhancement Process: A weak microwave signal with a power below -40 dB is input to the detection device using a vector network analyzer, forming an enhanced microwave magnetic field within the resonant cavity and exciting the magneton mode in the magnetic material. Under the control of feedback gain, the photon-magneton coupling effect is significantly enhanced. Throughout the entire magnetic field scanning range, the transmission spectral line maintains an extremely narrow linewidth of approximately 10 kHz, indicating that the system possesses an ultra-high spectral resolution better than 10 kHz. The coupling system, including the resonant cavity and the magnetic material, enables the observation of weak magneton modes that were previously difficult to distinguish; such as Figure 2 As shown in (c), near magnetic fields of 60mT and 90mT, the two low-damped magnon modes are cavity coupled with the resonant cavity, and appear as two bistable loops in the spectrum.

[0031] Step 4: Signal Detection and Pattern Analysis The first port of the vector network analyzer inputs microwaves into the detection device, and the second port of the vector network analyzer receives the transmitted microwaves after some of the microwave energy has been absorbed by the detection device. The ratio of the power of the transmitted microwaves to the power of the output microwaves is the transmission parameter S. 21 ; Under a fixed external magnetic field, the transmission parameter S 21 The change in microwave frequency is plotted as a transmission spectral line. By analyzing the frequency shift and linewidth information of the resonance peaks in the transmission spectra measured under different magnetic fields, the characteristics of the coupling mode of the coupled system as a function of the magnetic field are obtained. Based on the dynamic equations of the cavity-magnon coupling system, the resonance characteristics and coupling behavior of different magnon modes are extracted. Within the strong coupling region, the coherent coupling strength between the magnon and the cavity is significantly greater than their respective intrinsic dissipation rates, satisfying the strong coupling criterion. Specifically, the coupling system formed by the magnon and the high-quality factor cavity exhibits an anti-crossover characteristic in its resonance peak frequency as tuned by the applied magnetic field; while the coupling system formed by the magnon and the self-sustaining resonant cavity shows a bistable loop behavior in its resonance peak frequency evolution with the magnetic field. Utilizing this differentiated spectral line evolution characteristic, high-sensitivity detection and high-precision mode identification of multiple magnon eigenmodes can be achieved. Example 6

[0032] The difference between the working process of the gain resonant cavity weak magneton mode detection device based on an external feedback loop described in Example 5 is as follows: In step 2, adjusting the operating voltage of the low-noise amplifier to change the amplifier's gain means that the low-noise amplifier's turn-on voltage is 3.93V and its rated operating voltage is 8V. Within the operating voltage adjustment range of 3.93V to 8V, the device gain increases from 13.2dB to 26.6dB.

[0033] In step 4, the frequency shift and linewidth information of the resonance peaks in the transmission spectra measured under different magnetic fields are analyzed to obtain the characteristics of the coupling mode of the coupled system as a function of the magnetic field. This includes: performing Lorentz fitting on the transmission spectra to extract the evolution law of the resonance frequency and the full width at half maximum (FWHM) of the resonance peak as a function of the applied magnetic field; based on this evolution law, the coupling strength, dispersion relation and linewidth modulation characteristics of the photon-magneton coupling system are further analyzed to accurately characterize the dynamic evolution behavior of the intrinsic modes of the coupled system as a function of the magnetic field. Example 7

[0034] The operation process of the gain resonant cavity weak magneton mode detection device based on an external feedback loop as described in any of Examples 1-4 includes: System construction and operating condition settings: A two-dimensional van der Waals magnetic material chromium chloride sheet is placed in the local magnetic field enhancement region of the signal line of the coplanar waveguide resonant cavity to fully couple it with the microwave magnetic field inside the cavity; at the same time, an external static magnetic field is applied to the system along the direction of the signal line, and the system is operated in a low-temperature environment to control the resonance conditions of the magnetic mode and ensure measurement stability.

[0035] Establishment and State Control of the Active Resonant Cavity: A closed external feedback loop is constructed using two directional couplers and a linear low-noise amplifier to provide adjustable gain for the resonant cavity. By adjusting the amplifier bias voltage, compensation for intracavity losses is achieved, enabling the resonant cavity to operate in a high-quality factor state (e.g., ...). Figure 2 (as shown in (a)) and self-sustaining state (as shown in (a)) Figure 2 Switching between (b) and (as shown in the middle) significantly compresses the equivalent linewidth and enhances the system's response to weak signals. Figure 2 Achieved under voltage regulation ( Figure 2 (a) High-quality factor status and ( Figure 2 (b) Transmission spectra of the self-excited oscillating resonator and the transmission spectra of the CrCl3 magnon mode coupled with the active resonator at 2K temperature as a function of magnetic field. Figure 2 (c) In this figure, the horizontal axis represents the applied magnetic field, the vertical axis represents the microwave frequency, and the coloring represents the transmission parameter S. 21 .

[0036] Magneton excitation and signal enhancement process: A weak microwave signal is input to the system using a vector network analyzer, forming an enhanced microwave magnetic field within the resonant cavity, which excites the magneton mode in chromium chloride. Under the action of feedback gain, the photon-magneton coupling process is strengthened. The stable and extremely narrow linewidth ensures the high resolution of the cavity magneton coupling system in the spectrum, enabling the observation of weak magneton modes that were originally difficult to resolve, such as... Figure 2 As shown in (c), near magnetic fields of 60mT and 90mT, the two low-damped magnon modes are cavity coupled with the resonant cavity, and appear as two bistable loops in the spectrum.

[0037] Signal detection and mode analysis: Transmission parameters (S) of the system are acquired using a vector network analyzer. 21 By analyzing the response spectrum as a function of frequency and applied magnetic field, the resonance characteristics and coupling behavior of different magneton modes can be extracted, enabling highly sensitive detection and accurate identification of various magneton modes.

[0038] This invention introduces an external feedback gain mechanism to extend a traditional passive microwave resonator into a gain resonator system with tunable active characteristics, thereby significantly improving the detection capability of weak magneton modes. Unlike existing technologies that rely on high quality factor or cryogenic environments to improve signal resolution, this invention uses a closed feedback loop consisting of a directional coupler and a low-noise amplifier at room temperature to dynamically compensate for the cavity losses in cryogenic environments. This allows the system to be continuously adjustable between a high quality factor state and a self-sustaining state, thereby altering the equivalent damping and spectral characteristics of the resonator. Based on this, the active feedback drastically compresses the resonant linewidth and improves the signal-to-noise ratio, enabling the clear differentiation and identification of weak magneton modes that were previously masked by spectral broadening or strong magneton modes.

Claims

1. A gain resonant cavity weak magneton mode detection device based on an external feedback loop, characterized in that, include: Cavity magnetic subsystem, external feedback loop and signal readout system; The cavity magnetosystem includes a resonant cavity and a magnetic material. The resonant cavity is any one of a complementary open-loop resonant cavity, an open-loop resonant cavity, a microstrip cross resonant cavity, a Fabry-Perot resonant cavity, and a dielectric resonant cavity. The magnetic material is a material that generates magnetic resonance under microwave driving. The external feedback loop includes a low-noise amplifier, a directional coupler, an adjustable phase shifter, and a coaxial transmission line. The external feedback loop forms a closed-loop structure with the input and output ports of the resonant cavity. By adjusting the operating voltage of the low-noise amplifier to control the gain, the dynamic control of the resonant cavity characteristics can be achieved, thereby overcoming the loss limitation of the passive resonant cavity. The signal readout system uses a variety of devices with microwave signal analysis capabilities.

2. The gain resonant cavity weak magneton mode detection device based on an external feedback loop according to claim 1, characterized in that, The signal readout system is a vector network analyzer, spectrum analyzer, or oscilloscope.

3. The gain resonant cavity weak magneton mode detection device based on an external feedback loop according to claim 1, characterized in that, The directional coupler is replaced by a circulator or a power divider.

4. The gain resonant cavity weak magneton mode detection device based on an external feedback loop according to claim 1, characterized in that, The resonant cavity is a planar microwave resonant cavity based on a coplanar waveguide structure. In the central region of the resonant cavity, the current density is locally increased by narrowing the signal line width, so that the microwave magnetic field is locally enhanced in the signal line and the gap between the signal line and the ground line. The magnetic material is a two-dimensional van der Waals antiferromagnetic material chromium chloride. The magnetic material is placed in the form of a thin sheet above the distribution area of ​​the locally enhanced microwave magnetic field of the signal line in the resonant cavity to achieve efficient magnetic excitation and coupling. An external static magnetic field is applied along the signal line of the resonant cavity to precisely control the resonance conditions of the magnetic mode; The resonant cavity is connected to a low-noise amplifier via two directional couplers, forming a closed external feedback loop. This external feedback loop is placed at room temperature and continuously provides adjustable gain to the resonant cavity in a low-temperature environment. By adjusting the operating voltage of the low-noise amplifier, partial or complete compensation of the cavity loss can be achieved, enabling the detection device to controllably switch between a high-quality factor state and a self-sustaining state, thereby significantly changing the equivalent linewidth of the resonant cavity and its response characteristics to magnetic signals. In addition, the detection device is connected to an external vector network analyzer as a detection unit, which inputs a weak detection signal through the coupling port of the directional coupler and collects the transmission parameter S. 21 It is used to characterize the spectral response of the resonant cavity-magnetic spectral coupling system; by measuring and analyzing the transmission spectrum under different external magnetic field conditions and different operating states, it can achieve highly sensitive detection and accurate resolution of multiple magnetic spectral modes.

5. The gain resonant cavity weak magneton mode detection device based on an external feedback loop according to claim 4, characterized in that, In the central region of the resonant cavity, by narrowing the width of the signal line from 1.14 mm to 0.4 mm, the local current density is increased by 2-3 times, which in turn increases the magnetic field energy density of the microwave magnetic field in the signal line and the gap between the signal line and the ground line by 5-6 times.

6. The working process of the gain resonant cavity weak magneton mode detection device based on an external feedback loop according to any one of claims 1-5, characterized in that, include: Step 1: Detection device construction and operating condition setting: Place the magnetic material at the narrowing point of the signal line in the central region of the resonant cavity signal line to fully couple the magnetic material with the microwave magnetic field inside the resonant cavity; at the same time, apply an external static magnetic field along the direction of the resonant cavity signal line to ensure that the resonant frequency of the magnon mode in the magnetic material is within the frequency range of the vector network analyzer under the control of the external static magnetic field, and operate in an environment below the magnetic ordering temperature of the magnetic material, so as to control the resonance condition of the magnon mode and ensure measurement stability; Step 2: Establishment and State Control of Active Resonant Cavity: A closed external feedback loop is constructed through two directional couplers and a low-noise amplifier to provide adjustable gain for the resonant cavity; the low-noise amplifier is supplied with operating voltage by a voltage source, and adjusting the operating voltage of the low-noise amplifier changes the amplifier's amplification factor, realizing incomplete and complete compensation of the gain for the cavity loss, so that the resonant cavity switches between a high-quality factor state and a self-sustaining state. The cavity in the self-sustaining state is a resonant cavity that spontaneously radiates microwave signals outward. Step 3: Magneton Excitation and Signal Enhancement Process: A weak microwave signal with a power below -40dB is input to the detection device using a vector network analyzer to form an enhanced microwave magnetic field in the resonant cavity, which excites the magneton mode in the magnetic material; the coupling system includes the resonant cavity and the magnetic material, so that the weak magneton mode can be observed; Step 4: Signal Detection and Pattern Analysis The first port of the vector network analyzer inputs microwaves into the detection device, and the second port of the vector network analyzer receives the transmitted microwaves after some of the microwave energy has been absorbed by the detection device. The ratio of the power of the transmitted microwaves to the power of the output microwaves is the transmission parameter S. 21 ; In a fixed external magnetic field, the transmission parameter S 21 The transmission spectrum is plotted as a function of the microwave frequency; By analyzing the frequency shift and linewidth information of the resonance peaks in the transmission spectra measured under different magnetic fields, the characteristics of the coupling mode of the coupled system as a function of the magnetic field are obtained. Based on the dynamic equations of the resonant cavity and magnon coupling system, the resonance characteristics and coupling behavior of different magnon modes are extracted.

7. The working process of the gain resonant cavity weak magneton mode detection device based on an external feedback loop according to claim 6, characterized in that, In step 2, adjusting the operating voltage of the low-noise amplifier to change the amplifier's gain means that the low-noise amplifier's turn-on voltage is 3.93V and its rated operating voltage is 8V. Within the operating voltage adjustment range of 3.93V to 8V, the device gain increases from 13.2dB to 26.6dB.

8. The working process of the gain resonant cavity weak magneton mode detection device based on an external feedback loop according to claim 6 or 7, characterized in that, In step 4, the frequency shift and linewidth information of the resonance peaks in the transmission spectra measured under different magnetic fields are analyzed to obtain the characteristics of the coupling mode of the coupled system as a function of the magnetic field. This includes: performing Lorentz fitting on the transmission spectra to extract the evolution law of the resonance frequency and the full width at half maximum (FWHM) of the resonance peak as a function of the applied magnetic field; based on this evolution law, the coupling strength, dispersion relation and linewidth modulation characteristics of the photon-magneton coupling system are further analyzed to characterize the dynamic evolution behavior of the intrinsic modes of the coupled system as a function of the magnetic field.

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