Is it possible to extract the magnetic correlation length from the low-temperature magnetic structure refined using neutron powder diffraction data? Is it related to the FWHM of the magnetic peaks?
Magnetic correlation length can be calculated from neutron powder diffraction data by analyzing the magnetic scattering in the diffraction pattern. Neutrons have a magnetic moment, which allows them to interact with the magnetic moments in a material. In the case of a magnetic material, the neutron diffraction pattern will contain both structural scattering and magnetic scattering.
One common method to calculate the magnetic correlation length from neutron powder diffraction data is to use the Rietveld refinement method. This method uses a combination of structural and magnetic models to fit the diffraction pattern, and allows for the extraction of the magnetic correlation length and other magnetic parameters such as the magnetic structure and magnetic moment.
In the Rietveld refinement method, the magnetic scattering is modeled as a sum of magnetic Bragg peaks, where the intensity, position and width of the peaks are determined by the magnetic correlation length and the magnetic structure. The correlation length can be calculated by fitting the width of the magnetic peaks and comparing it to the width of the corresponding structural peaks.
Another method to calculate the magnetic correlation length is to use the method of moments by fitting the magnetic scattering to the Ornstein-Zernike form of the magnetic correlation function, where the correlation length is related to the decay rate of the magnetic correlations.
In both methods, a good quality of data, high resolution and high statistics is needed to accurately determine the correlation length, and the refinement should be done with the help of a suitable software package.
It's worth noting that the magnetic correlation length is a statistical concept, and it may not reflect the real physical size of the magnetic domains. Additionally, these methods are based on the assumption that the magnetic correlations are isotropic which may not be the case for some materials.
Ponniah Vajeeston Thank you so much for the detailed description. I have a few follow-up questions.
In the 1st method, how do we interpret the widths of the magnetic vs structural peaks? For example, if the magnetic peaks are less broad than the structural peaks (in general), what information do we obtain from it and how is it related to the correlation length mathematically?
Also, how will this analysis be affected if the peaks are resolution-limited?
Could you also be so kind as to point me to some literature sources where both types of analyses are elucidated? Many thanks!
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