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|Title:||ALS-CXRO Seminar Series | Akio Kotani|
|When:||09/25/2013 3:00 PM - 4:00 PM|
|Description:||ALS/CXRO Seminar Series|
Wed, Sept 25, 2013
15-253 Conf Rm
Photon Factory, IMSS, High Energy Accelerator Organization, Tsukuba, Ibaraki 305-0801, Japan
X-ray Absorption and Magnetic Circular Dichroism Spectra
of Mixed Valence Eu Compounds in High Magnetic Fields
The Eu ion in Eu compounds EuNi2(Si1-xGex)2 (x = 0.79, 0.82 etc.) exhibits a mixed-valence character between Eu2+ and Eu3+ at low temperatures, but the valence number changes rapidly by applying high magnetic fields at about 30 T (which is denoted by field-induced valence transition). High-magnetic- fields XAS and XMCD techniques have been developed recently and used to study the field-induced valence transition of EuNi2(Si0.18Ge0.82)2. However, the valence number measured by hard-X-ray Eu L3 XAS  cannot be interpreted consistently with the magnetization data. Furthermore, an unexpectedly large XMCD signal was measured for the Eu3+ component of the Eu L3 XMCD . In order to resolve these problems, new theoretical calculations and new soft-X-ray Eu M4,5 XAS and XMCD experiments were carried out, where the calculations take into account the effects of the first-order nature of the field-induced valence transition, the Van Vleck paramagnetism for the Eu3+ component, and magnetic impurities [2,3]. The calculated results well reproduced the experimental magnetization curve, and the new soft-X-ray experiments  gave the valence and magnetization data which agree with those of new calculations. These theoretical and experimental results [2.3] indicate that the Van Vleck paramagnetism is too small to explain the large XMCD signal measured by hard-X-ray Eu L3 XMCD. Finally, we extend successfully the theory to describing the temperature-induced valence transition of this material.
------------------------------------dthe temperature-induced valence transition of this material.
 Y. H. Matsuda et al., J. Phys. Soc. Jpn. 77, 054713 (2008); Phys. Rev. Lett. 103, 046402 (2009).
 T. Nakamura et al., J. Phys. Soc. Jpn. 81, 114702 (2012).
 A. Kotani and T. Nakamure, J. Phys. Soc. Jpn. 82, 044710 (2013).