Theory of Electric Quadrupole Transition in the XMCD Spectra at the Yb L3 Edge of Mixed Valence Yb Compounds in High Magnetic Fields

Abstract

The spectra of X-ray magnetic circular dichroism by the electric quadrupole transition (EQ-XMCD) are theoretically studied at the Yb L3 edge of mixed valence compounds, YbInCu4 and YbAgCu4, around the field-induced valence transition in high magnetic fields. Using a new formulation with a single impurity Anderson model, which directly connects the EQ-XMCD spectra with the weights of the Yb 4f angular momentum jz in the ground state, we show that the EQ-XMCD intensity of YbAgCu4 is more than twice as large as that of YbInCu4. This explains the reason for that the EQ-XMCD spectra was very recently measured successfully for YbAgCu4, whereas no experimental evidence of EQ-XMCD has so far been obtained for YbInCu4. Different EQ-XMCD intensities for the two materials and a peculiar field dependence of EQ-XMCD intensities are discussed on the basis of the weights of jz in the ground state.