SPring-8, the large synchrotron radiation facility

A joint research group consisting of Hiroyuki Nojiri, Professor at the Institute for Materials Research, Tohoku University, Yasuhiro Matsuda, Associate Professor at the Institute for Solid State Physics, The University of Tokyo, Toshiya Inami, Senior Scientist at Japan Atomic Energy Agency, Motohiro Suzuki, Senior Scientist at Japan Synchrotron Radiation Research Institute, and Akihiro Mitsuda, Associate Professor at the Graduate School of Sciences, Kyushu University, dramatically broke the previous world record^*1 for the strength of a magnetic field in X-ray magnetic circular dichroism (XMCD) spectroscopy^*2 to measure element-specific magnetic properties.  They succeeded in carrying out an experiment under the ultrahigh magnetic field of 40 T, approximately one millionfold higher than the geomagnetic field.^*3  This result was achieved by combining the high-brilliance X-rays of SPring-8 and an originally developed miniature high-pulsed-magnetic-field generator (Figs. 1 and 2).  Unlike the large pulsed-magnetic-field generators usually used, miniature high-pulsed-magnetic-field generators enable prompt experiments anywhere without the need to modify currently used devices or to use new experimental infrastructure.  The generator developed by Tohoku University has now been introduced worldwide.  Owing to the development of this device, the XMCD method, which had previously been used only for a limited range of ferromagnetic substances, is expected to be widely applied to the research of general magnetic substances at a rapid pace.  In previous studies on magnetic materials such as magnetic memories, the XMCD method of measuring element-specific magnetic properties was difficult to use unless the target element exhibited highly magnetic properties, which mostly depends on chance.  Now, by using the miniature high-pulsed-magnetic-field generator, the XMCD method can be used to evaluate the element-specific magnetic properties for any magnetic material, making it possible to quickly select an appropriate composition for a given application from among various compositions.  In addition, it is expected that the combination of microscopic information obtained from XMCD with the calculation results of electron states will enable the effective design of new materials.

In this research, the XMCD technology was applied to a magnetic material containing europium, a rare-earth element.  Europium exhibits a mysterious characteristic; it sometimes shows strongly magnetic properties and other times loses them depending on the quantum-mechanical^*4 mixture of the two electron states with different valences^*5 (Fig. 3).   The selective observation of these two microscopic magnetic states was previously difficult.  The scientists of this group were the first to discover, using the developed device, that the magnetic responses for these two states completely differ under high magnetic fields.  This demonstrated that the developed method of high-magnetic-field XMCD spectroscopy is a powerful method for clarifying specific magnetic properties of various substances.  This method is expected to greatly contribute to the design and development of new magnetic materials used for new types of magnetic memories and sensors in the future.

The research achievements were published in the online version of the international academic journal of the American Institute of Physics, Physical Review Letters, on 28 July 2009.

Publication:
"X-Ray Magnetic Circular Dichroism of a Valence Fluctuating State in Eu at High Magnetic Fields"
Y. H. Matsuda, Z. W. Ouyang, H. Nojiri, T. Inami, K. Ohwada, M. Suzuki, N. Kawamura, A. Mitsuda, and H. Wada
Physical Review Letters 103, 046402 (2009), published online 21 July 2009