A method for refining a complex magnetic structure by neutron diffraction

Abstract

The application provides a complex magnetic structure step-by-step approximation refining method based on neutron diffraction, which is suitable for scientific instrument and material research industry, mainly aims at research and development, performance evaluation and quality control of new magnetic materials, realizes high-precision analysis of complex magnetic structure (including magnetic moment size and arrangement direction) by providing a systematic step-by-step approximation refining strategy, and provides an important experimental characterization method and means for basic research and industrial application of magnetic materials, and more specifically, aims at improving the reliability and efficiency of complex magnetic structure analysis through systematic step design and improved optimization algorithm, including data acquisition and preliminary analysis, basic model construction, step-by-step approximation refining strategy, model complication and final refining result confirmation. The application is expected to provide a more solid experimental basis for the research of complex magnetic materials and promote the further development of the field of magnetic material science.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of neutron scattering experiments, and specifically to the technical field of structure characterization of magnetic materials, and particularly relates to a complex magnetic structure analysis method based on neutron diffraction technology. BACKGROUND

[0002] In the field of magnetic material science, accurate analysis of magnetic structure is of great significance for understanding the origin of material magnetism, predicting material performance, and developing new magnetic materials. Due to its unique advantages, neutron scattering technology has become an indispensable experimental method for studying complex magnetic structures. As a probe, neutrons not only have a magnetic moment, but also have small mass and electrical neutrality, and can directly interact with the unpaired electron magnetic moment in the material, thus 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 the material, which makes it particularly important in the study of complex magnetic systems such as non-collinear magnetic structure, helical magnetic structure, and antiferromagnetic structure. Neutron diffraction patterns can directly reflect the periodic arrangement of magnetic moments and provide details of the magnetic structure that other methods cannot obtain. In addition, the strong penetration ability of neutrons allows them to obtain 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 the data processing of magnetic structure analysis, the application of GSAS (General Structure Analysis System) and other software tools is quite widespread. The GSAS software not only supports Rietveld refinement of crystal structure, but also extends to the field of magnetic structure analysis, with the advantages of user-friendly interface, high calculation efficiency, and support for multiple diffraction data formats. However, in the processing of 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 local minimum, affecting the reliability of the results; at the same time, the calculation efficiency of the software will be significantly reduced when processing a large amount of diffraction data, especially when studying the temperature evolution of magnetic structure.

[0005] Although the steps of traditional analysis of magnetic structures are systematic, there are still many problems in practical applications. First, the convergence of complex magnetic structure refinement is a technical problem that needs to be solved. Especially when dealing with three-dimensional non-collinear magnetic moment configuration systems, due to the strong coupling effect of x, y and z direction magnetic moment components, the refinement process is often difficult to converge or easily trapped in local minimum. Second, the existing data analysis method has limitations in dealing with multi-dimensional magnetic moment components, lacks effective algorithm to decouple the magnetic moment contribution in different directions, and the uncertainty evaluation system of the refinement result is not perfect. In addition, although polarized neutron scattering can provide additional magnetic moment orientation information, how to effectively integrate these information with conventional neutron diffraction data to realize the collaborative analysis of multi-scale characterization data is still a problem to be solved.

[0006] In order 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 multiple verification systems have become research hotspots. However, despite these advances, a more systematic, efficient and reliable magnetic structure analysis method is still needed to meet the needs of complex magnetic material research. SUMMARY

[0007] To solve the above problems, the present application provides a step-by-step approximation refinement method for complex magnetic structure based on neutron diffraction, which is suitable for scientific instruments and materials research industry, mainly for the research and development, performance evaluation and quality control of new magnetic materials, and provides a systematic step-by-step approximation refinement strategy to realize high-precision analysis of complex magnetic structure (including magnetic moment size and arrangement direction), and provides an important experimental characterization method and means for basic research and industrial application of magnetic materials. More specifically, the purpose is to improve the reliability and efficiency of complex magnetic structure analysis through systematic step design and improved optimization algorithm. The 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 present application is expected to provide a more solid experimental basis for the research of complex magnetic materials and promote the further development of the field of magnetic material science.

[0008] To solve the technical problem, the technical scheme adopted by the present application is: a step-by-step approximation refinement method for complex magnetic structure 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 spectrum of the sample, determining the magnetic propagation vector k, and combining crystallographic knowledge to analyze the symmetry to select the most suitable magnetic space group;

[0010] b) base model building: starting from the simplest magnetic moment arrangement, setting physically reasonable initial magnetic moment size and direction;

[0011] c) stepwise refinement strategy: sequentially performing magnetic moment size optimization, magnetic moment direction optimization, and coupled optimization of magnetic moment size and direction;

[0012] d) model complication: according to the fitting effect, gradually increasing the complexity of the model, and if necessary, introducing new magnetic propagation vectors or considering modulation structures;

[0013] e) final refinement result confirmation: confirming that the final obtained magnetic structure solution has good R-factor values, and the structure model has reasonable physical meaning.

[0014] The stepwise refinement strategy in step c) specifically includes:

[0015] First round of refinement: only optimize the magnetic moment size, keeping the magnetic moment direction fixed;

[0016] Direction optimization: after obtaining reliable magnetic moment size, release the direction parameter for optimization, while keeping the optimized magnetic moment size relatively fixed;

[0017] Coupled optimization: on the basis of certain optimization of magnetic moment size and direction, simultaneously perform coupled optimization of magnetic moment direction and size.

[0018] In the first round of refinement, for multiple magnetic atomic positions, adopt the method of "fixing part and optimizing others" to gradually optimize.

[0019] The process of model complication in step d) includes considering multiple magnetic ions, and starting from magnetic moment size optimization when introducing a new complex factor.

[0020] The basis for final refinement result confirmation in step e) includes Rwp and Rp factor values, and the physical reasonableness of the structure model.

[0021] The method further includes, in each stage of the stepwise refinement process, screening the optimal magnetic structure model by comparing the fitting degrees of different models.

[0022] 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.

[0023] The method further includes, after final refinement result confirmation, verifying the reasonableness of the obtained magnetic structure model through systematic error analysis and other complementary characterization means.

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

[0025] The beneficial effects of the present application are: the complex magnetic structure step-by-step approximation refinement method based on neutron diffraction proposed by the present application has significant beneficial effects in the field of magnetic material structure characterization technology, which is embodied in the following aspects:

[0026] (I) Improve the accuracy and reliability of complex magnetic structure analysis: the present application overcomes the problem of easily falling into local minimum in traditional magnetic structure refinement through systematic step-by-step approximation strategy. By optimizing the size and direction of 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. The method introduces physically reasonable initial model and constraint conditions, combined with intelligent parameter correlation function, making the refinement process of complex magnetic structure more controllable and reliable, avoiding the unreasonable solution with physical meaning in traditional method.

[0027] (II) Improve the optimization efficiency and applicability: compared with traditional methods, the step-by-step optimization strategy of the present application involves fewer parameters in each step, significantly speeding up the convergence speed and improving the optimization efficiency. This method is not only suitable for complex magnetic structure, but also widely applicable to various types of magnetic materials, such as anti-perovskite system, showing wide applicability. Avoid over-parameterization: the present application effectively avoids over-parameterization by gradually increasing complexity from simple model and verifying the physical meaning in each optimization step, ensuring the reasonableness and simplicity of the obtained magnetic structure model.

[0028] (III) Provide complete parameter optimization process and operation guide: the present application first proposes a systematic step-by-step approximation strategy, establishing a complete parameter optimization process, providing a clear operation path and guide for researchers.

[0029] (IV) Enhance the traceability and verifiability of the results: the optimization process of the present application is controllable, and the parameter adjustment is more targeted, the results have good traceability. Through multiple verification methods, such as cross verification of data under different conditions and checking the physical reasonableness of magnetic moment size, the reliability of the results is ensured.

[0030] (V) Promote the development of magnetic material research and application: the present application provides an important experimental characterization method and means for the research and development, performance evaluation and quality control of new magnetic materials, which helps to understand the magnetic nature of materials in depth and promotes the application and development of magnetic materials in the fields of science and technology and industry.

[0031] In summary, the step-by-step approximation refinement method for complex magnetic structure based on neutron diffraction provided by the present application has remarkable beneficial effects in the field of magnetic material structure characterization technology, not only improving the accuracy and reliability of complex magnetic structure analysis, but also improving the optimization efficiency and applicability, avoiding over-parameterization problems, 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 application. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is a flowchart of analyzing complex magnetic structure in the present application. DETAILED DESCRIPTION

[0033] As Figure 1 shown, the present application provides a step-by-step approximation refinement method for complex magnetic structure based on neutron diffraction, which aims to overcome the convergence problem in traditional magnetic structure refinement, improve the accuracy and reliability of complex magnetic structure analysis. The following will describe the specific embodiments of the present application in detail.

[0034] Step one, data acquisition and preliminary analysis (1) sample preparation and neutron diffraction experiment

[0035] Select appropriate magnetic material samples, such as anti-perovskite Mn3GaC, Mn3Zn0.5Ge0.5N, etc., and use solid phase sintering method or other appropriate preparation method to prepare samples. Use the general powder diffraction spectrometer (GPPD) of China Spallation Neutron Source (CSNS) or other neutron diffraction facilities to collect the neutron diffraction spectrum of the sample under the set temperature (such as magnetic order temperature) and pressure conditions.

[0036] (2) Preliminary data analysis

[0037] After obtaining the neutron diffraction data, the magnetic propagation vector k is determined by analyzing the diffraction data, which is a key parameter to describe the periodicity of the magnetic moment arrangement. Combined with crystallographic knowledge, symmetry analysis is performed to select the most suitable magnetic space group.

[0038] Step two, basic model construction

[0039] (1) Initial magnetic structure model setting

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

[0041] Step three, step-by-step approximation refinement strategy

[0042] First round refinement: Magnetic moment size optimization. In the initial stage, only the magnetic moment size is optimized, while the direction is kept fixed. For multiple magnetic atom positions, a "fix part, optimize others" approach can be taken, optimizing gradually. By comparing the goodness of fit (such as Rwp, Rp factor) under different magnetic moment sizes, the optimal magnetic moment size is determined.

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

[0044] Coupling optimization: Based on the optimization of the previous two steps, the direction and size of the magnetic moment are simultaneously optimized. Carefully analyze the correlation between parameters to ensure that the optimization results have reasonable physical meaning.

[0045] Step four, model complexity (I) Introduce 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 if necessary, introduce new magnetic propagation vectors. In some cases, modulation structure may need to be considered.

[0047] (II) Re-optimization

[0048] Each time a new complex factor is introduced, it needs to start from the magnetic moment size optimization 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] Five, final refinement result confirmation

[0050] (I) Goodness of fit evaluation

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

[0052] (II) Verification of physical meaning

[0053] Check whether the final obtained magnetic structure model has reasonable physical meaning. By comparing experimental data and other characterization methods (such as magnetization measurement, Mossbauer spectrum, nuclear magnetic resonance, etc.), verify the reliability of the magnetic structure model.

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

[0055] In this embodiment, the Mn3GaC sample is prepared by solid phase sintering method. The diffraction data at 5K and 0.5Gpa pressure are collected on GPPD of CSNS. Through step-by-step approximation refinement method, the magnetic moment size is determined to be 1.96μB, the spin direction is the direction with an angle of 80° with the

[111] axis, and the magnetic structure is the spin-inclined antiferromagnetism (CAFM).

[0056] Embodiment two: analysis of complex magnetic structure of manganese-based anti-perovskite nitride Mn3Zn0.5Ge0.5N

[0057] In this embodiment, the Mn3Zn0.5Ge0.5N sample is prepared by high-temperature solid phase sintering method. The sub-diffraction data are collected in TOF mode at 2-300K on GPPD, and the wavelength is between The possible magnetic space group is determined by a three-step approximation method, starting from the simplest collinear structure and introducing a non-collinear model. Finally, a complex non-collinear antiferromagnetic structure is obtained at low temperature of 10K, with a magnetic moment size of 3.26(3)μB and an Rwp factor of 6.15%.

[0058] The feasibility and superiority of the method are fully verified through the detailed demonstration of two typical embodiments, 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 methods such as checking the physical reasonableness of the magnetic moment size and verifying the symmetry of the magnetic structure are used to ensure the reliability of the results. According to the specific material properties and experimental conditions, the parameters are appropriately adjusted and optimized to obtain the best results. The correlation between parameters is paid attention to, and the problem of unstable fitting and overfitting caused by excessive parameterization is avoided.

[0059] In summary, the present application proposes a step-by-step approximation refinement method for complex magnetic structure based on neutron diffraction, which effectively overcomes the convergence problem in traditional magnetic structure refinement through systematic step design and step-by-step optimization strategy. The method 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 excessive 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 application.

Claims

1. A method for the 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: Neutron diffraction techniques are used to obtain diffraction patterns of the samples, determine the magnetic propagation vector k, and perform symmetry analysis combined with crystallographic knowledge to select the most suitable magnetic space group; b) Basic model construction: Starting from the simplest magnetic moment arrangement configuration, set the 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 coupled magnitude and direction of the magnetic moment; d) Model complexity: Based on the fitting effect, gradually increase the complexity of the model, introduce new magnetic propagation vectors or consider modulation structures; 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 refinement based on neutron diffraction by successive approximation 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, while the direction of the magnetic moment is kept fixed; Direction optimization: After obtaining a reliable magnetic moment, release the direction parameters for optimization while keeping the optimized magnetic moment relatively fixed. Coupling optimization: Based on the optimization of the magnitude and direction of the magnetic moment, the direction and magnitude of the magnetic moment are coupled and optimized at the same time.

3. The method for complex magnetic structure refinement based on neutron diffraction by successive approximation 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 refining others" was adopted to optimize step by step.

4. The method for successive approximation refinement of complex magnetic structures based on neutron diffraction according to claim 1, characterized in that: The process of increasing the complexity of the model in step d) includes considering the case of 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 successive approximation refinement of complex magnetic structures 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 successive approximation refinement of complex magnetic structures based on neutron diffraction according to claim 1, characterized in that: The method further 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 successive approximation refinement of complex magnetic structures 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 successive approximation refinement of complex magnetic structures 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 results are confirmed.

9. The method for successive 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.

Images