X-Ray Magnetic Circular Dichroism of a Valence Fluctuating State in Eu at High Magnetic Fields

X-ray magnetic circular dichroism (XMCD) at the Eu L edge in two compounds exhibiting valence fluctuation, namely EuNi2(Si0.18Ge0.82)(2) and EuNi2P2, has been investigated at high magnetic fields of up to 40 T. A distinct XMCD peak corresponding to the trivalent state (Eu3+), whose ground state is nonmagnetic (J = 0), was observed in addition to the main XMCD peak corresponding to the magnetic (J = 7/2) divalent state (Eu2+). This result indicates that the 5d electrons belonging to both valence states are magnetically polarized. It was also found that the ratio P-5d(3+)/P-5d(2+) between the polarization of 5d electrons (P-5d) in the Eu3+ state and that of Eu2+ depends on the material. The possible origin of the XMCD and an explanation of the material dependence of P-5d(3+)/P-5d(2+) are discussed in terms of hybridization between the conduction electrons and the f electrons.