World’s First Realization of Soft X-ray Spectroscopic Experiments in Ultrahigh Magnetic Fields (Press Release)
- Release Date
- 30 May, 2011
- BL25SU (Soft X-ray Spectroscopy of Solid)
Japan Synchrotron Radiation Research Institute
Tohoku University
The Institute for Solid State Physics, The University of Tokyo
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Scientists of the Japan Synchrotron Radiation Research Institute (JASRI; President, Tetsuhisa Shirakawa), jointly with those of Tohoku University (President, Akihisa Inoue) and The Institute for Solid State Physics, The University of Tokyo (Director, Yasuhiro Iye), have successfully conducted soft X-ray*1 spectroscopic experiments under ultrahigh magnetic fields of 21 T (2.1×105 Gauss) using the SPring-8 Beamline, Soft X-ray Spectroscopy of Solids (BL25SU), for the first time in the world. This enables magnetic analysis using soft X-ray magnetic circular dichroism (XMCD)*2 for almost all practical magnetic materials, including strong neodymium magnets. XMCD spectroscopy enables the analysis of the atomic magnet (magnetic moment*3) for each element to be examined, and has such a high sensitivity that the magnetism of one atomic layer can be detected. The most fundamental and important information of the target magnetic material that is necessary to determine its properties can be obtained by examining the changes in the direction and magnitude of the magnetic moment with respect to the strength of magnetic fields. No significant changes in magnetic moment are observed unless the magnetic field is sufficiently high; hence, high magnetic fields are required to comprehensively examine the properties of various materials. However, to date, the highest magnetic field that could be used in soft XMCD experiments was only 10 T, which had not been updated for over 10 years. In this study, the research group tackled the development of a technique to markedly increase the maximum magnetic field. The scientists adopted the pulsed magnetic field method, in which ultrahigh magnetic fields can be generated, in a very short time (0.05 s), by rapidly discharging the electricity stored in a power unit into a coil used for generating magnetic fields. However, it was difficult to precisely measure weak signals of the detected soft X-rays, i.e., an extremely small current of about 10-9 A, under the severe noise environment of a large current being discharged at once, similarly to lightening. Focusing on the fact that the amount of noise generated is proportional to the temporal gradient in the current, thorough countermeasures against noise were taken by, for example, decreasing the gradient to one-tenth or less than that of the conventional method and modifying the wiring of signal cables. Consequently, they succeeded in experimentally measuring XMCD under ultrahigh magnetic fields of 21 T, which is at least twofold higher than the highest conventional magnetic field. The use of the developed measurement technique will lead to the clarification of the role of rare-earth elements, the price of which is increasing, in magnets, such as dysprosium (Dy) used as a component of neodymium magnets. Research on the development of inexpensive elements (ubiquitous elements) that are alternatives to rare-earth elements is expected to progress. The achievements of this study were obtained by the joint research group led by Tetsuya Nakamura (Senior Scientist) of JASRI, Yasuo Narumi (Associate Professor) of Tohoku University, and Koichi Kindo (Professor) of The University of Tokyo. The research results were published online in the international journal of the Japan Society of Applied Physics, Applied Physics Express (APEX), on 24 May 2011. Publication: |
<<Glossary>>
*1 Soft/hard X-rays
There is no clear difference in the definitions of soft and hard X-rays. In this study, soft X-rays refer to X-rays with an energy of approximately 800 eV (a wavelength of approximately 1 nm), whereas hard X-rays refer to those with an energy 10-fold higher than that of soft X-rays.
*2 X-ray magnetic circular dichroism (XMCD)
When circularly polarized X-rays are irradiated onto a magnetic material, the absorption of soft X-rays depends on whether the direction of circular polarization is clockwise or counterclockwise. Because the difference in absorption reflects the magnetic properties of the material, it is used for magnetic measurement techniques with soft X-rays. XMCD of each element to be examined can be obtained by adjusting the energy of soft X-rays to a particular value, enabling the analysis of particular elements.
*3 Magnetic moment
Magnetic moment is a vector indicating the magnitude and direction (from S to N poles) of an atom as a magnet.
<<Figures>>
and schematic of cross-sectional image of measurement chamber (right)
A coil is constantly cooled by liquid nitrogen because it emits heat during the generation of magnetic fields. A sample is set in a vacuum pipe that penetrates the coil. The current with the charge equivalent to the amount of photoelectrons emitted from the sample in proportion to the absorption of soft X-rays is amplified through a current amplifier. Namely, the current flowing through the current amplifier is in proportion to the absorption of soft X-rays.
For explanation, see the main text.
The black line represents the raw data of the measurement result, and the red circles are plots of the average of the raw data for each 0.25 T to increase the accuracy.
measurements similar to those in the case of Fig. 2 for different soft X-ray energies
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