Electronic states near the fermi level in the antiferromagnetic and ferromagnetic spinels of Zn1-xCuxCr2Se4;: 0.0 ≤ x ≤ 1.0

The electronic states of normal-type spinels in Zn1-xCuxCr2Se4 have been studied by X-ray absorption spectroscopy near the K-edge of Zn, Cu, Cr and Se ions. It is found that characteristic white lines occur near the X-ray absorption threshold for Zn and Se ions, but not for Cu and Cr ions. It is also found that the white lines show a slight energy shift, which depends on the Cu concentration. The energy shifts mean that Fermi level gradually approaches the top region of the valence band of Se2-, on increasing the Cu ions. The substitution of Zn2+ with Cu1+ ions increases the number of positive carriers, holes. The holes occupying the top region of the valence band strongly correlate with Cr4+, which forms an empty orbital in the 3d-band of Cr3+ and exchanges the valence electrons with Cr3+. It is interpreted that the ferromagnetism in Zn1-xCuxCr2Se4 is made by double-exchange interaction between Cr3+ and Cr4+ ions and that holes contribute to the electronic conductivity of Zn1-xCuxCr2Se4.