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 ${\mathrm{EuNi}}_2({\mathrm{Si}}_{0.18}{\mathrm{Ge}}_{0.82}{)}_2$ and ${\mathrm{EuNi}}_2{\mathrm{P}}_2$, has been investigated at high magnetic fields of up to 40 T. A distinct XMCD peak corresponding to the trivalent state (${\mathrm{Eu}}^{3+}$), 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 (${\mathrm{Eu}}^{2+}$). 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 ${\mathrm{Eu}}^{3+}$ state and that of ${\mathrm{Eu}}^{2+}$ 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.

Figure 1

(a) XMCD and XAS spectra at various magnetic fields at 5 K for the $L_2$ edge. XAS spectra are plotted in such a way that the absorption at 7.598 keV becomes zero. (b) XMCD and XAS spectra at various magnetic fields at 5 K for the $L_3$ edge. XAS spectra are plotted in such a way that the absorption at 6.956 keV becomes zero.

Figure 2

(a) Magnetic field dependence of the integrated XMCD intensities of ${\mathrm{Eu}}^{2+}$ and ${\mathrm{Eu}}^{3+}$ states for the $L_2$ edge. (b) The degree of magnetic polarization of $5d$ electrons is plotted as a function of the magnetic field. Magnetization measured at 4.2 K [14] is shown for comparison.

Figure 3

(a) XMCD spectra in ${\mathrm{EuNi}}_2{\mathrm{P}}_2$ at high magnetic fields. The XAS spectra at 3 and 40 T, which are plotted in such a way that the absorption intensity becomes zero at 7.598 eV, are also shown. (b) The degree of magnetic polarization of the $5d$ electrons, as well as the magnetization measured at 4.2 K, are plotted as functions of the magnetic field.