SPring-8, the large synchrotron radiation facility

The Japan Synchrotron Radiation Research Institute (JASRI), in collaboration with Kumamoto University, the National Institute for Materials Science (NIMS), and The University of Tokyo, has applied Bayesian spectroscopy to the analysis of the spectrum obtained from the magnetic Compton scattering^*1 of pure iron, which is a typical metal used in magnetic materials. As a result, they succeeded in developing a new analysis technique for determining the magnetic moment by magnetic Compton scattering in a measurement time one-twentieth of the conventional measurement time while maintaining the same accuracy as conventional techniques.

Magnetic Compton scattering is defined by the spectral difference obtained using right and left circularly polarized X-rays^*2. The obtained spectrum contains information on spin magnetic moment^*3 and 3d and 4s electron orbitals^*4. The spin magnetic moment is obtained by integrating the spectral intensity. The information on the shapes of 3d and 4s electron orbitals is obtained by decomposing the spectrum. The spin magnetic moment is determined by measuring the magnetic Compton scattering and can be used in improving the performance of magnetic materials. The signals from magnetic Compton scattering are so weak that it takes a long time to obtain a sufficient spectrum for acquiring the above-mentioned information. However, magnetic Compton scattering is the most suitable method to obtain the bulk information of the electronic state. For these reasons, a technique that enables a reduction in measurement time while maintaining the accuracy of the obtained information has been desired.

Our group applied Bayesian spectroscopy, which is based on Bayes’ theorem, to the analysis of the spectrum obtained from magnetic Compton scattering. We determined the measurement time required to obtain the magnitude of spin magnetic moment with the desired accuracy. The estimation of the accuracy, which has been impossible with conventional analysis techniques, is enabled by Bayesian spectroscopy. We have built a framework for finishing the measurement when the desired accuracy is achieved. Using this framework, the measurement time required to evaluate the magnitude of the spin magnetic moment with an accuracy to the second decimal place is one-twentieth of the conventional measurement time. Namely, the measurement that conventionally took almost one day can be completed in about one hour. This enables the measurements of many materials manufactured under various conditions. Such measurements will provide guidelines for the optimization of the material manufacturing conditions, which will promote the research and development of magnetic materials.

The newly developed analysis technique based on Bayesian spectroscopy will enable a marked reduction in measurement time and promote the research and development of magnetic materials using magnetic Compton scattering. Also, with this analysis technique, the measurement time can be determined automatically by a computer without the need for human intervention, which will significantly contribute to the development of automatic measurement systems in the future.

This study was conducted by a joint research group including Yuichi Yokoyama (Postdoctoral Researcher), Naruki Tsuji (Research Scientist), and Masaichiro Mizumaki (Senior Scientist) of JASRI, Ichiro Akai (Professor) of Kumamoto University, Kenji Nagata (Senior Researcher) of NIMS, and Masato Okada (Professor) of the University of Tokyo. Their achievements will be published in the online edition of the Journal of Physical Society of Japan on 30 August 2021.

Publication
Title: Bayesian Orbital Decomposition and Determination of End Condition for Magnetic Compton Scattering
Authors: Yuichi Yokoyama, Naruki Tsuji, Ichiro Akai, Kenji Nagata, Masato Okada, and Masaichiro Mizumaki
Journal of Physical Society of Japan
Published August 30, 2021
DOI: 10.7566/JPSJ.90.094802