X-ray magnetic circular dichroism measurement system and measurement method

Abstract

The application discloses an X-ray magnetic circular dichroism (XMCD) measurement system and a measurement method thereof. The XMCD measurement system comprises a signal generation module, a power amplifier module, an electromagnet module, a signal acquisition module and a lock-in amplifier module. The XMCD signal is modulated by an alternating magnetic field, and the lock-in amplifier technology is combined, so that the weak XMCD signal is effectively avoided from being submerged in a high absorption spectrum background, high-precision measurement of the weak XMCD signal is realized, and the measurement system and the measurement method have the advantages of simple structure, low construction cost and low debugging difficulty.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of synchrotron radiation soft X-ray magnetic circular dichroism measurement, and particularly relates to an X-ray magnetic circular dichroism measurement system and an X-ray magnetic circular dichroism measurement method. BACKGROUND

[0002] Synchrotron radiation soft X-ray spectroscopy mainly includes X-ray absorption spectroscopy (XAS), synchrotron radiation photoelectron emission spectroscopy (SRPES) and X-ray emission spectroscopy (XES), which is a powerful means for studying atomic / electronic structure and chemical properties of functional materials. Synchrotron radiation soft X-ray spectroscopy has a wide range of applications in the study of atomic / electronic structure of many functional materials, such as two-dimensional ferromagnetic materials, spintronics materials, oxide heterojunctions, lithium ion battery electrode materials, etc.

[0003] Synchrotron radiation soft X-ray magnetic circular dichroism (XMCD) spectroscopy is an important magnetic characterization technology. XMCD method has element resolution and can distinguish the contribution of spin magnetic moment and orbital magnetic moment of a single element to the macroscopic magnetic moment. It plays an irreplaceable role in the study of magnetic materials and spintronics. In synchrotron XMCD spectroscopy measurement, the XMCD signal is obtained by subtracting two X-ray absorption spectra under different test conditions. Currently, there are two physically equivalent XMCD measurement methods: (1) magnetize the sample using a fixed direction magnetic field, and then measure the absorption spectrum using left-handed and right-handed circular polarization directions of soft X-ray respectively. The difference spectrum of the two absorption spectra is the absorption spectrum contribution related to the magnetic moment, i.e. the XMCD signal; (2) magnetize the sample using magnetic fields in opposite directions twice, and then measure the absorption spectrum using a fixed circular polarization direction of soft X-ray after each magnetization. The difference spectrum of the two absorption spectra is the XMCD signal.

[0004] However, the amplitude of the XMCD signal of many important magnetic material systems accounts for a very low proportion (less than 1%) in the total X-ray absorption spectrum signal. The extraction of the XMCD signal has a low signal-to-background ratio. Especially for thin film / interface systems with low proportion of elements to be measured, the weak XMCD signal is often submerged in the high absorption spectrum signal background, making it difficult to accurately measure. Japan's Spring-8 synchrotron developed a phase-locked amplification XMCD experimental method based on X-ray circular polarization direction modulation. This method uses two undulators to generate left-handed and right-handed circular polarization direction soft X-ray incident on the sample, and uses phase-locked amplification method to extract the XMCD signal. However, this experimental method needs to run on a specially designed double-undulator beamline. Due to the complex structure, high construction cost and high debugging difficulty, such double-undulator beamlines are rarely used on synchrotron devices around the world. In addition, the circular polarization direction modulation frequency of the double-undulator beamline is limited by the working frequency of the kick magnet, which is generally not higher than 100 Hz. SUMMARY

[0005] In view of this, the present invention needs to provide an X-ray magnetic circular dichroism (XMCD) measurement system. This system uses an alternating magnetic field to modulate the sample XMCD signal and performs lock-in amplification measurement. It does not require upgrading the light source and beamline system. High-precision measurement of weak XMCD signals can be achieved by combining a data acquisition system with lock-in amplification.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention first provides an X-ray magnetic circular dichroism measurement system, which includes:

[0008] The signal generation module receives control commands and emits a low-power signal, which is divided into two paths: one as a reference signal and the other as a modulation signal.

[0009] A power amplifier module, wherein the power amplifier module receives a modulation signal and amplifies the modulation signal into a high-power alternating excitation current of the same frequency;

[0010] An electromagnet module, which generates an alternating magnetic field under the action of a high-power alternating excitation current and acts on the sample to be tested;

[0011] The signal acquisition module is used to acquire the X-ray absorption spectrum signal of the sample to be tested;

[0012] And a lock-in amplifier module, which receives a reference signal and an X-ray absorption spectrum signal respectively, and separates the AC XMCD signal from the background signal.

[0013] In a further embodiment, the parameters of the low-power signal include waveform and frequency, wherein the waveform is one of square wave, sine wave, triangle wave and pulse wave.

[0014] In a further embodiment, the signal acquisition module is a current detection module, a fluorescence detection module, or a light emission detection module.

[0015] A further embodiment also includes a control and reading module, which issues control commands to control the signal generation module and reads the XMCD signal from the lock-in amplifier module.

[0016] This invention further provides an X-ray magnetic circular dichroism measurement method, comprising the following steps:

[0017] Acquire a low-power signal and split it into two paths: one as a reference signal and the other as a modulation signal.

[0018] The modulation signal is amplified into a high-power alternating excitation current of the same frequency, and an alternating magnetic field is generated based on the alternating excitation current and applied to the sample under test.

[0019] Synchrotron radiation X-rays are directed onto the sample to be tested, and the X-ray absorption spectrum signal of the sample is acquired.

[0020] Based on the reference signal and the X-ray absorption spectrum signal, a lock-in amplification operation is performed to separate the AC XMCD signal from the background signal;

[0021] Read the XMCD signal.

[0022] In a further embodiment, the parameters of the low-power signal include waveform and frequency, wherein the waveform is one of square wave, sine wave, triangle wave and pulse wave.

[0023] In a further embodiment, the acquisition of the X-ray absorption spectrum signal can be achieved by acquiring the current, fluorescence, or luminescence signals of the sample to be tested.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] This invention utilizes alternating magnetic field modulation combined with lock-in amplification technology. First, the alternating magnetic field is used to modulate the XMCD signal into an AC signal with characteristic frequency and phase. Then, the phase-sensitive detection and low-pass filtering of the lock-in amplification technology are used to separate the AC XMCD signal from the DC absorption spectrum background signal, thereby realizing the measurement of weak XMCD signals.

[0026] The X-ray magnetic circular dichroism chromatograph measurement system of this invention can measure weak XMCD signals without upgrading the light source and beamline system. It features a simple structure, low construction cost, and easy debugging. Furthermore, the modulation frequency of existing measurement systems is limited by the operating frequency of the kicker magnet, with the highest reported modulation frequency being only 10Hz. The measurement system of this invention, utilizing an alternating magnetic field for modulation, can achieve a modulation frequency greater than 1kHz, and the higher the modulation frequency, the better the lock-in amplification effect. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the X-ray magnetic circular dichroism measurement system in a preferred embodiment of the present invention;

[0028] Figure 2 The image shows the XMCD spectrum of the iron-iron oxide composite film measured in this embodiment of the invention.

[0029] In the diagram: 101-Control computer, 102-Signal generator, 103-Power amplifier, 104-Detector, 105-Lock-in amplifier, 106-Electromagnet, 107-Sample to be tested. Detailed Implementation

[0030] The embodiments of the present invention are described in detail below. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0032] A preferred embodiment of the present invention discloses an X-ray magnetic circular dichroism measurement system, such as... Figure 1 The system includes a control computer 101, a signal generator 102, a power amplifier 103, a detector 104, a lock-in amplifier 105, and an electromagnet 106. This measurement system modulates the sample XMCD signal with an alternating magnetic field and performs lock-in amplification measurement. By using alternating magnetic field modulation combined with lock-in amplification technology, the AC XMCD signal is separated from the DC absorption spectrum background signal, thus realizing the measurement of weak XMCD signals. This measurement system does not require upgrading the light source and beamline. Since it uses an alternating magnetic field for modulation, the modulation frequency (i.e., the frequency of the AC XMCD signal) can be greater than 1kHz, and the higher the modulation frequency, the better the lock-in amplification effect.

[0033] The control computer 101 serves as the control and reading module of the measurement system. On one hand, it sends control commands to the signal generator 102 to control the signal generator 102; on the other hand, it reads the XMCD signal from the lock-in amplifier 105. It is understood that the control computer 101 also includes some software that matches its functions, which will not be described in detail here.

[0034] Signal generator 102, connected to control computer 101, receives control commands from control computer 101 and emits a low-power signal with a specific waveform and frequency. The low-power signal is split into two paths: one is sent as a reference signal to lock-in amplifier 105, and the other is sent as a modulation signal to power amplifier 103. The waveform and frequency of the emitted low-power signal can be selected or adjusted according to specific experimental and sample conditions (such as the magnitude of the applied magnetic field, the signal strength of the sample, and the magnetic properties of the sample), and therefore are not particularly limited. The waveform described herein can be one of a square wave, sine wave, triangle wave, or pulse wave.

[0035] The power amplifier 103 is connected to the signal generator 102 and is used to receive the modulation signal from the signal generator 102. The modulation signal entering the power amplifier 103 is amplified into a high-power alternating excitation current of the same frequency and then fed into the electromagnet 106.

[0036] Furthermore, the electromagnet 106 generates an alternating magnetic field under the action of a high-power alternating excitation current. This alternating magnetic field acts on the sample 107 to be tested, and simultaneously synchrotron X-rays are radiated onto the sample 107 to be tested.

[0037] Detector 104 is used to acquire the X-ray absorption spectrum signal of the sample 107 under test and sends the X-ray absorption spectrum signal to lock-in amplifier 105. Depending on the X-ray absorption spectrum signal testing method, the type of detector 104 can be adjusted. Specifically, detector 104 can be a current detector, a fluorescence detector, or a luminescence detector; any instrument capable of testing the X-ray absorption spectrum signal of the sample 107 under test can be used in this invention. It is understood that detector 104 integrates a readout system to read out the X-ray absorption spectrum signal based on the tested signal.

[0038] An alternating magnetic field is applied to the sample 107, and the intensity of the X-ray absorption spectrum signal of the sample 107 changes with time (i.e., it has an AC component). The net value of this change is the intensity of the XMCD signal. Furthermore, since the above change has a specific frequency, lock-in amplification technology can be used for precise measurement.

[0039] Furthermore, the lock-in amplifier 105 is connected to the control computer 101, the signal generator 102, and the detector 104, respectively. It receives the reference signal from the signal generator 102 and the X-ray absorption spectrum signal from the detector 104. Phase-sensitive detection and low-pass filtering are used to separate the AC XMCD signal from the DC absorption spectrum background signal, achieving the separation of the weak XMCD signal. The control computer 101 then reads the XMCD signal from the lock-in amplifier 105.

[0040] The above measurement system does not require a specially designed dual-undulator beamline. By utilizing an alternating magnetic field combined with lock-in amplification technology, the alternating magnetic field acting on the sample 107 modulates the XMCD signal of the sample 107 into an alternating signal with a specific frequency, separating the XMCD signal from the absorption spectrum background signal in the spectrum. This allows for precise extraction and measurement of the XMCD signal through lock-in amplification. Lock-in amplification technology has excellent weak signal detection capabilities, and the higher the modulation frequency, the greater the separation between the measured signal and the background signal in the spectrum, resulting in better measurement performance. This measurement system employs an alternating magnetic field modulation method, achieving modulation frequencies above 1 kHz, thus enabling accurate separation of the weak XMCD signal from the background signal and achieving precise measurement of the weak XMCD signal.

[0041] This invention further provides an X-ray magnetic circular dichroism measurement method, the main steps of which are as follows:

[0042] A low-power signal is acquired and split into two paths: one path is used as a reference signal and the other path is used as a modulation signal. The low-power signal has a specific waveform and frequency, and the waveform can be any one of square wave, sine wave, triangle wave and pulse wave.

[0043] The modulation signal is amplified into a high-power alternating excitation current of the same frequency, and an alternating magnetic field is generated based on this alternating excitation current and applied to the sample under test.

[0044] Synchrotron radiation X-rays are directed onto the sample to be tested and the X-ray absorption spectrum signal of the sample to be tested is acquired. The acquisition of the X-ray absorption spectrum signal is not particularly limited and can be acquired by conventional methods in the art. Specific methods include, but are not limited to, detecting the current, fluorescence or luminescence signal of the sample to be tested.

[0045] Lock-in amplification is performed based on the reference signal and the X-ray absorption spectrum signal to separate the AC XMCD signal from the background signal;

[0046] Read the XMCD signal.

[0047] The X-ray magnetic circular dichroism (XMCD) measurement method uses an alternating magnetic field to modulate the XMCD signal of the sample. The highest modulation frequency is greater than 1 kHz, and the higher the modulation frequency, the better the lock-in amplification effect, thereby realizing the precise measurement of weak XMCD signals.

[0048] The technical solution of the present invention will be further described below with reference to specific embodiments. It should be noted that the specific embodiments below are only for illustrative purposes and do not limit the scope of the present invention in any way. In addition, unless otherwise specified, methods without specific conditions or steps are conventional methods, and the reagents and materials used can be obtained from commercial sources.

[0049] Embodiments

[0050] This embodiment discloses an X-ray magnetic circular dichroism measurement method, which is based on Figure 1 The X-ray magnetic circular dichroism spectroscopy measurement system shown is used, and the sample to be tested, 107, is an iron-iron oxide composite film.

[0051] The specific process is as follows:

[0052] The control computer 101 issues a control command, and the signal generator 102 emits a low-power signal with a square wave waveform and a frequency of 1kHz. The low-power signal is then split into two paths, one of which is used as a reference signal and enters the lock-in amplifier 105, and the other is used as a modulation signal and enters the power amplifier 103.

[0053] The power amplifier 103 amplifies the modulation signal into a high-power alternating excitation current with an amplitude of 7.5A, and feeds the alternating excitation current into the electromagnet 106;

[0054] Electromagnet 106 generates an alternating magnetic field with a frequency of 1kHz and an intensity of 1500Oe under the action of alternating excitation current, and acts on the sample to be tested 107, while synchrotron X-rays are radiated onto the sample to be tested 107.

[0055] The detector 104 measures the X-ray absorption spectrum signal of the sample in the form of sample current and sends it to the lock-in amplifier 105.

[0056] The lock-in amplifier 105 performs lock-in amplification on the reference signal and the X-ray absorption spectrum signal to separate the AC XMCD signal from the background signal.

[0057] The control computer 101 reads the XMCD signal from the lock-in amplifier 105.

[0058] The XMCD signal read is as follows Figure 2 As shown in the figure, it can be seen that in this embodiment, by using AC magnetic field modulation and lock-in amplification, the weak XMCD signal is effectively avoided from being buried in the background of the high absorption spectrum. The weak XMCD signal, which accounts for about 2.5% of the absorption spectrum intensity, can be accurately detected, and the XMCD spectrum has a high signal-to-noise ratio.

[0059] The above embodiments further illustrate that the X-ray magnetic circular dichroism chromatograph measurement system and method of the present invention can achieve high-precision measurement of weak XMCD signals.

[0060] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0061] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. An X-ray magnetic circular dichroism measurement system, characterized in that, include: The signal generation module receives control commands and emits a low-power signal, which is divided into two paths: one as a reference signal and the other as a modulation signal. A power amplifier module, wherein the power amplifier module receives a modulation signal and amplifies the modulation signal into a high-power alternating excitation current of the same frequency; An electromagnet module, which generates an alternating magnetic field with a frequency ≥1kHz under the action of a high-power alternating excitation current and applies it to the sample to be tested; The signal acquisition module is used to acquire the X-ray absorption spectrum signal of the sample to be tested; And a lock-in amplifier module, which receives a reference signal and an X-ray absorption spectrum signal respectively, and separates the AC XMCD signal from the background signal.

2. The X-ray magnetic circular dichroism chromatographic measurement system as described in claim 1, characterized in that, The parameters of the low-power signal include waveform and frequency, wherein the waveform is one of square wave, sine wave, triangle wave and pulse wave.

3. The X-ray magnetic circular dichroism chromatographic measurement system as described in claim 1, characterized in that, The signal acquisition module is a current detection module, a fluorescence detection module, or a light emission detection module.

4. The X-ray magnetic circular dichroism chromatographic measurement system according to any one of claims 1-3, characterized in that, It also includes a control and reading module, which issues control commands to control the signal generation module and reads the XMCD signal from the lock-in amplifier module.

5. An X-ray magnetic circular dichroism measurement method, which is based on the X-ray magnetic circular dichroism measurement system according to any one of claims 1-4, characterized in that, The measurement method includes the following steps: Acquire a low-power signal and split it into two paths: one as a reference signal and the other as a modulation signal. The modulation signal is amplified into a high-power alternating excitation current of the same frequency, and an alternating magnetic field is generated based on the alternating excitation current and applied to the sample under test. Synchrotron radiation X-rays are directed onto the sample to be tested, and the X-ray absorption spectrum signal of the sample is acquired. Based on the reference signal and the X-ray absorption spectrum signal, a lock-in amplification operation is performed to separate the AC XMCD signal from the background signal; Read the XMCD signal.

6. The X-ray magnetic circular dichroism measurement method as described in claim 5, characterized in that, The parameters of the low-power signal include waveform and frequency, wherein the waveform is one of square wave, sine wave, triangle wave and pulse wave.

7. The X-ray magnetic circular dichroism measurement method as described in claim 5, characterized in that, The acquisition of the X-ray absorption spectrum signal can be achieved by acquiring the current, fluorescence, or luminescence signals of the sample under test.

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