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

Abstract

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(Si0.18Ge0.82)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(Si0.18Ge0.82)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 L2-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].