XMCD spectroscopy on valence fluctuating and heavy fermion compounds in very high magnetic fields up to 40 T

L-edge X-ray magnetic circular dichroism (XMCD) and X-ray absorption spectra (XAS) in several rare-earth elements have been studied in high magnetic fields up to 40 T using a pulsed magnet. XMCD spectrum of Eu in a typical valence fluctuating compound, EuNi₂(Si_0.18Ge _0.82)₂, shows a characteristic two peak structure, reflecting the valence fluctuation. However, in another valence fluctuating compound, YbInCu₄, it is found that the XMCD spectrum of Yb shows only a single peak. In contrast to XMCD, two absorption bands in XAS are observed in both EuNi₂(Si_0.18Ge_0.82) ₂ and YbInCu₄. The intensity ratio between the two absorption bands changes significantly with increasing magnetic field in these materials, suggesting the field-induced valence change. The high magnetic field XMCD and XAS measurements have also been conducted in an antiferromagnetic heavy fermion compound CeRh₂Si₂. The Ce valence is found to be nearly trivalent and insensitive to magnetic field. The XMCD at Ce L ₂-edge increases rapidly around 26 T corresponding to the metamagnetic transition. The XMCD spectra in CeRh₂Si₂ at high magnetic fields show only a single peak as was reported in a heavy fermion ferromagnetic compound CeRu₂Ge₂ [1].