Complex magnetic structure successive approximation refinement method based on neutron diffraction

Abstract

The invention provides a complex magnetic structure successive approximation refinement method based on neutron diffraction, which is suitable for the scientific instrument and material research industry, mainly aims at research and development, performance evaluation and quality control of novel magnetic materials, and provides a systematic successive approximation refinement strategy. High-precision analysis of complex magnetic structures (including magnetic moment size and arrangement direction) is realized, important experimental characterization methods and means are provided for basic research and industrial application of magnetic materials, and more specifically, the method aims at realizing high-precision analysis of complex magnetic structures (including magnetic moment size and arrangement direction) through systematic step design and an improved optimization algorithm. Comprising the steps of data acquisition and preliminary analysis, basic model construction, successive approximation of a refinement strategy, model complication and final refinement result confirmation, and reliability and efficiency of complex magnetic structure analysis are improved. The method provided by the invention is expected to provide a firmer experimental foundation for research of complex magnetic materials and promote further development of the field of magnetic material science.

Description

Technical Field

[0001] The present invention relates to the technical field of neutron scattering experiments, specifically belonging to the technical field of magnetic material structure characterization, and particularly relates to a method for analyzing complex magnetic structures based on neutron diffraction technology. Background Art

[0002] In the field of magnetic material science, the accurate analysis of magnetic structures is of crucial significance for understanding the origin of magnetism in materials, predicting material properties, and developing new magnetic materials. Neutron scattering technology, due to its unique advantages, has become an indispensable experimental means for studying complex magnetic structures. As a probe, neutrons not only have magnetic moments but also have a small mass and are electrically neutral, enabling them to directly interact with the unpaired electron magnetic moments in materials, thereby providing magnetic structure information at the atomic scale.

[0003] Compared with other characterization techniques such as X-ray and electron microscopy, neutron scattering can simultaneously obtain the long-range crystal structure and magnetic structure of materials. This characteristic makes it particularly important in the study of complex magnetic systems such as non-collinear magnetic structures, helical magnetic structures, and antiferromagnetic structures. Neutron diffraction patterns can directly reflect the periodic arrangement of magnetic moments, providing magnetic structure details that are difficult to obtain by other methods. In addition, the strong penetration ability of neutrons enables it to obtain the intrinsic magnetic information of bulk materials, avoiding the influence of surface effects on the results, which is particularly important for the study of the magnetic properties of bulk materials.

[0004] In terms of data processing for magnetic structure analysis, software tools such as GSAS (General Structure Analysis System) have been widely used. GSAS software not only supports the Rietveld refinement of crystal structures but also extends to the field of magnetic structure analysis, with advantages such as a user-friendly operation interface, high calculation efficiency, and support for multiple diffraction data formats. However, when dealing with complex magnetic structures, existing software such as GSAS still faces many challenges. For example, for non-collinear magnetic structures or modulated magnetic structures with multiple magnetic propagation vectors, the refinement process is prone to falling into local minima, affecting the reliability of the results; at the same time, the calculation efficiency of the software will be significantly reduced when dealing with a large amount of diffraction data, especially when studying the temperature evolution of magnetic structures.

[0005] Although the steps for traditional magnetic structure analysis are systematic, there are still many problems in practical applications. First, the refinement convergence of complex magnetic structures is a technical problem that urgently needs to be solved. Especially when dealing with systems with three-dimensional non-collinear magnetic moment configurations, due to the strong coupling effect of the magnetic moment components in the x, y, and z directions, the refinement process often fails to converge or is prone to falling into local minima. Second, the existing data analysis methods have limitations in dealing with multi-dimensional magnetic moment components, lacking effective algorithms to decouple the magnetic moment contributions in different directions, and the uncertainty evaluation system for the refinement results is not perfect. In addition, although polarized neutron scattering can provide additional magnetic moment orientation information, how to effectively integrate this information with conventional neutron diffraction data to achieve the collaborative analysis of multi-scale characterization data remains an unsolved problem.

[0006] To overcome these technical bottlenecks, researchers have been exploring more advanced refinement strategies and data analysis methods. Among them, establishing a step-by-step optimization scheme based on physical constraints, developing intelligent model screening algorithms, and improving the multiple verification system have become research hotspots. However, despite these progress, a more systematic, efficient, and reliable magnetic structure analysis method is still needed to meet the requirements of complex magnetic material research. Summary of the Invention

[0007] To solve the above problems, the present invention proposes a step-by-step approximation refinement method for complex magnetic structures based on neutron diffraction, which is applicable to the scientific instrument and material research industries, mainly for the research and development, performance evaluation, and quality control of new magnetic materials. By providing a systematic step-by-step approximation refinement strategy, it realizes the high-precision analysis of complex magnetic structures (including magnetic moment magnitude and arrangement direction), provides important experimental characterization methods and means for the basic research and industrial applications of magnetic materials. More specifically, it aims to improve the reliability and efficiency of complex magnetic structure analysis through systematic step design and improved optimization algorithms. This method fully considers the coupling relationship between magnetic moment components, introduces constraint conditions based on physical principles, and adopts a step-by-step optimization strategy to ensure the convergence of the refinement process and the rationality of the results. The proposal of the present invention is expected to provide a more solid experimental foundation for the research of complex magnetic materials and promote the further development of the field of magnetic material science.

[0008] To solve the technical problems, the technical solution adopted by the present invention is: a step-by-step approximation refinement method for complex magnetic structures based on neutron diffraction, the method comprising the following steps:

[0009] a) Data acquisition and preliminary analysis: Using neutron diffraction technology to obtain the diffraction pattern of the sample, determining the magnetic propagation vector k, and performing symmetry analysis in combination with crystallographic knowledge to select the most suitable magnetic space group;

[0010] b) Construction of the basic model: Starting from the simplest magnetic moment arrangement configuration, set the physically reasonable initial magnitudes and directions of the magnetic moments;

[0011] c) Step-by-step approximation refinement strategy: Sequentially perform optimization of the magnetic moment magnitudes, optimization of the magnetic moment directions, and coupled optimization of the magnetic moment magnitudes and directions;

[0012] d) Model complication: According to the fitting effect, gradually increase the complexity of the model. When necessary, introduce new magnetic propagation vectors or consider modulated structures;

[0013] e) Confirmation of the final refined result: Confirm that the finally obtained magnetic structure solution has a good R-factor value and the structural model has reasonable physical significance.

[0014] The step-by-step approximation refinement strategy in step c) specifically includes:

[0015] First-round refinement: Only optimize the magnetic moment magnitudes while keeping the magnetic moment directions fixed;

[0016] Direction optimization: After obtaining reliable magnetic moment magnitudes, release the direction parameters for optimization while keeping the optimized magnetic moment magnitudes relatively fixed;

[0017] Coupled optimization: On the basis of certain optimizations of both the magnetic moment magnitudes and directions, perform coupled optimization of the magnetic moment directions and magnitudes simultaneously.

[0018] In the first-round refinement, for the case of multiple magnetic atom positions, adopt the method of "fixing some and refining others" to gradually optimize.

[0019] The process of model complication in step d) includes considering the case of multiple magnetic ions, and when introducing each new complex factor, start from the optimization of the magnetic moment magnitudes again.

[0020] The basis for confirming the final refined result in step e) includes the Rwp and Rp factor values, as well as the physical rationality of the structural model.

[0021] The described method also includes screening the optimal magnetic structure model by comparing the goodness of fit of different models at each stage of the step-by-step approximation refinement process.

[0022] In step a), determine the diffraction characteristics near the magnetic phase transition temperature by analyzing the diffraction data to assist in selecting the magnetic space group.

[0023] The described method also includes, after confirming the final refined result, verifying the rationality of the obtained magnetic structure model through systematic error analysis and other complementary characterization means.

[0024] The described complementary characterization means include at least one of magnetization measurement, Mössbauer spectroscopy, and nuclear magnetic resonance.

[0025] The beneficial effects of the present invention are as follows: The method for gradually approaching and refining complex magnetic structures based on neutron diffraction proposed by the present invention has significant beneficial effects in the technical field of magnetic material structure characterization, which are specifically reflected in the following aspects:

[0026] (1) Improving the accuracy and reliability of complex magnetic structure analysis: Through a systematic step-by-step approximation strategy, the present invention effectively overcomes the problem of easily falling into local minima in traditional magnetic structure refinement. By optimizing the magnitude and direction of the magnetic moment step by step, the coupling interference between parameters is significantly reduced, ensuring the stability of the optimization process and the accuracy of the results. A physically reasonable initial model and constraint conditions are introduced in the method, combined with an intelligent parameter correlation function, making the refinement process of complex magnetic structures more controllable and reliable, and avoiding physically unreasonable solutions that may be obtained by traditional methods.

[0027] (2) Enhancing the optimization efficiency and applicability: Compared with traditional methods, the step-by-step optimization strategy of the present invention involves fewer parameters in each step, significantly accelerating the convergence speed and improving the optimization efficiency. This method is not only applicable to complex magnetic structures but also widely applicable to various types of magnetic materials, such as the inverse perovskite system, etc., demonstrating broad applicability. Avoiding the problem of over-parameterization: By gradually increasing the complexity from a simple model and verifying the physical meaning in each step of optimization, the present invention effectively avoids the problem of over-parameterization, ensuring the rationality and simplicity of the obtained magnetic structure model.

[0028] (3) Providing a complete parameter optimization process and operation guide: The present invention first proposes a systematic step-by-step approximation strategy and establishes a complete parameter optimization process, providing researchers with a clear operation path and guide.

[0029] (4) Enhancing the traceability and verifiability of the results: The optimization process of the present invention is controllable, the parameter adjustment is more targeted, and the results have good traceability. Through multiple verification means, such as cross-verifying data under different conditions and checking the physical rationality of the magnetic moment magnitude, the reliability of the results is ensured.

[0030] (5) Promoting the development of magnetic material research and applications: The present invention provides an important experimental characterization method and means for the research and development, performance evaluation, and quality control of new magnetic materials, helping to deeply understand the magnetic nature of materials and promoting the application and development of magnetic materials in the fields of science and technology and industry.

[0031] In summary, the method for gradually approaching and refining complex magnetic structures based on neutron diffraction proposed by the present invention has significant beneficial effects in the field of magnetic material structure characterization technology. It not only improves the accuracy and reliability of complex magnetic structure analysis, but also enhances the optimization efficiency and applicability, avoids over-parameterization problems, provides a complete parameter optimization process and operation guide, enhances the traceability and verifiability of results, and promotes the development of magnetic material research and applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic flow chart for analyzing complex magnetic structures in the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] As Figure 1 shown, the present invention proposes a method for gradually approaching and refining complex magnetic structures based on neutron diffraction, which aims to overcome the convergence problems existing in traditional magnetic structure refinement and improve the accuracy and reliability of complex magnetic structure analysis. The following will describe the specific embodiments of the present invention in detail with reference to specific examples.

[0034] Step 1. Data acquisition and preliminary analysis (1) Sample preparation and neutron diffraction experiment

[0035] Select appropriate magnetic material samples, such as inverse perovskite Mn3GaC, Mn3Zn0.5Ge0.5N, etc., and prepare the samples by solid-phase sintering method or other appropriate preparation methods. Use the General Powder Diffraction Spectrometer (GPPD) of the China Spallation Neutron Source (CSNS) or other neutron diffraction facilities to collect the neutron diffraction patterns of the samples under set temperature (such as magnetic ordering temperature) and pressure conditions.

[0036] (2) Preliminary data analysis

[0037] After obtaining the neutron diffraction data, determine the magnetic propagation vector k by analyzing the diffraction data, which is a key parameter describing the periodicity of magnetic moment arrangement. Combine crystallographic knowledge to conduct symmetry analysis and select the most suitable magnetic space group.

[0038] Step 2. Construction of the basic model

[0039] (1) Setting of the initial magnetic structure model

[0040] Start from the simplest magnetic moment arrangement configuration, such as a collinear magnetic structure, and set physically reasonable initial magnetic moment magnitudes and directions.

[0041] Step 3. Gradual approximation and refinement strategy

[0042] First-round fine-tuning: Optimization of the magnetic moment magnitude. In the initial stage, only the magnetic moment magnitude is optimized while keeping the magnetic moment direction fixed. For the case of multiple magnetic atom positions, the method of "fixing some and refining others" can be adopted to gradually carry out the optimization. By comparing the goodness of fit (such as Rwp, Rp factors) at different magnetic moment magnitudes, the optimal magnetic moment magnitude is determined.

[0043] Direction optimization: After obtaining a relatively reliable magnetic moment magnitude, release the direction parameters (within the range allowed by the space group) for optimization. Keep the optimized magnetic moment magnitude relatively fixed and gradually improve the accuracy of the model by adjusting the direction parameters.

[0044] Coupling optimization: On the basis of the first two optimizations, simultaneously carry out coupling optimization of the direction and magnitude of the magnetic moment. Carefully analyze the correlation between parameters to ensure that the optimization results have reasonable physical meanings.

[0045] Step 4. Model complication (1) Introduction of multiple magnetic ions and new magnetic propagation vectors

[0046] According to the fitting effect, gradually increase the complexity of the model. First, consider the case of multiple magnetic ions and introduce new magnetic propagation vectors when necessary. In some cases, a modulated structure may need to be considered.

[0047] (2) Re-optimization

[0048] Every time a new complex factor is introduced, it is necessary to start from the optimization of the magnetic moment magnitude again to ensure that the introduction of new parameters is necessary. Avoid over-parameterization of the model and ensure the controllability of the optimization process.

[0049] V. Confirmation of the final fine-tuning results

[0050] (1) Evaluation of the goodness of fit

[0051] After completing all optimization steps, evaluate the goodness of fit (such as Rwp, Rp factors) of the finally obtained magnetic structure solution. Ensure that the goodness of fit reaches an acceptable range.

[0052] (2) Verification of physical meanings

[0053] Check whether the finally obtained magnetic structure model has reasonable physical meanings. Verify the reliability of the magnetic structure model by comparing the experimental data with the results of other characterization methods (such as magnetization measurement, Mössbauer spectroscopy, nuclear magnetic resonance, etc.).

[0054] Example 1: Magnetic structure analysis of inverse perovskite Mn3GaC

[0055] In this embodiment, the Mn3GaC sample was prepared by the solid-phase sintering method. Diffraction data were collected at a magnetic ordering temperature of 5 K and a pressure of 0.5 GPa on the GPPD of CSNS. By the method of step-by-step approximation refinement, the magnitude of the magnetic moment was determined to be 1.96 μB, the spin direction was the direction with an angle of 80° with the

[111] axis, and the magnetic structure was canted antiferromagnetism (CAFM).

[0056] Example 2: Analysis of the complex magnetic structure of the manganese-based inverse perovskite nitride Mn3Zn0.5Ge0.5N

[0057] In this embodiment, the Mn3Zn0.5Ge0.5N sample was prepared by the high-temperature solid-phase sintering method. Neutron diffraction data were collected in the TOF mode at 2 - 300 K on the GPPD, and the wavelength was in between. By using a systematic three-step approximation method, the possible magnetic space group was determined. Starting from the simplest collinear structure, a non-collinear model was introduced. Finally, a complex non-collinear antiferromagnetic structure was presented at a low temperature of 10 K, the magnitude of the magnetic moment was 3.26(3) μB, and the Rwp factor was 6.15%.

[0058] Through the detailed demonstration of two typical embodiments, the feasibility and superiority of the method of the present invention have been fully verified, providing a complete operation guide and reference basis for subsequent researchers. More specifically, by cross-verifying the data collected under different conditions, the reliability and consistency of the data are ensured. Multiple verification means such as checking the physical rationality of the magnitude of the magnetic moment and verifying the symmetry of the magnetic structure are used to ensure the reliability of the results. According to the specific material characteristics and experimental conditions, the parameters are appropriately adjusted and optimized to obtain the best results. Pay attention to the correlation between parameters to avoid problems such as unstable fitting and overfitting caused by over-parameterization.

[0059] In summary, the present invention proposes a step-by-step approximation refinement method for complex magnetic structures based on neutron diffraction. By means of systematic step design and step-by-step optimization strategies, the convergence problem existing in traditional magnetic structure refinement is effectively overcome. The method of the present invention has the advantages of high optimization efficiency, strong result reliability, wide applicability, etc. It has been successfully applied to the analysis of complex magnetic structures of various magnetic materials, not only improving the accuracy and reliability of complex magnetic structure analysis, but also enhancing the optimization efficiency and applicability, avoiding the problem of over-parameterization, providing a complete parameter optimization process and operation guide, enhancing the traceability and verifiability of the results, and promoting the development of magnetic material research and applications.

Claims

1. A method for stepwise approximation refinement of complex magnetic structures based on neutron diffraction, characterized by: The method comprises the following steps: a) Data acquisition and preliminary analysis: Use neutron diffraction technology to obtain the diffraction pattern of the sample, determine the magnetic propagation vector k, and combine crystallographic knowledge to perform symmetry analysis to select the most suitable magnetic space group; b) Basic model construction: starting from the simplest magnetic moment arrangement configuration, setting physically reasonable initial magnetic moment size and direction; c) Stepwise approximation refinement strategy: sequentially optimize the magnitude of the magnetic moment, optimize the direction of the magnetic moment, and optimize the coupling of the magnitude and direction of the magnetic moment; d) Model complexity: According to the fitting effect, the complexity of the model is gradually increased, and new magnetic propagation vectors are introduced or modulation structures are considered when necessary; e) Confirmation of final refinement results: Confirm that the final magnetic structure solution has a good R factor value and that the structural model has reasonable physical meaning.

2. The method for complex magnetic structure stepwise approximation refinement based on neutron diffraction according to claim 1, characterized in that: The stepwise approximation refinement strategy in step c) specifically includes: First round of refinement: Only the magnitude of the magnetic moment is optimized, keeping the direction of the magnetic moment fixed; Direction optimization: After obtaining a reliable magnetic moment size, release the direction parameters for optimization while keeping the optimized magnetic moment size relatively fixed; Coupling optimization: On the basis of certain optimization of the size and direction of the magnetic moment, the direction and size of the magnetic moment are coupled optimized at the same time.

3. The method for complex magnetic structure stepwise approximation refinement based on neutron diffraction according to claim 2, characterized in that: In the first round of refinement, for the position of multiple magnetic atoms, the method of "fixing some and repairing others" was adopted to optimize step by step.

4. The method for complex magnetic structure stepwise approximation refinement based on neutron diffraction according to claim 1, characterized in that: The process of complicating the model in step d) includes considering multiple magnetic ions and starting over from the optimization of the magnetic moment size each time a new complicating factor is introduced.

5. The method for complex magnetic structure stepwise approximation refinement based on neutron diffraction according to claim 1, characterized in that: The basis for confirming the final refinement results in step e) includes the Rwp and Rp factor values, as well as the physical rationality of the structural model.

6. The method for complex magnetic structure stepwise approximation refinement based on neutron diffraction according to claim 1, characterized in that: The method also includes screening the optimal magnetic structure model by comparing the goodness of fit of different models in each stage of the stepwise approximation refinement process.

7. The method for complex magnetic structure stepwise approximation refinement based on neutron diffraction according to claim 1, characterized in that: In step a), the diffraction characteristics near the magnetic phase transition temperature are determined by analyzing the diffraction data to assist in selecting the magnetic space group.

8. The method for complex magnetic structure stepwise approximation refinement based on neutron diffraction according to claim 1, characterized in that: The method also includes verifying the rationality of the obtained magnetic structure model through systematic error analysis and other complementary characterization methods after the final refinement result is confirmed.

9. The method for stepwise approximation refinement of complex magnetic structures based on neutron diffraction according to claim 8, characterized in that: The complementary characterization means include at least one of magnetization measurement, Mössbauer spectroscopy, and nuclear magnetic resonance.

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