Electronic structures of Zn$_{1-x}$Co$_x$O using photoemission and x-ray absorption spectroscopy

TL;DR

This study investigates the electronic structure of Zn$_{1-x}$Co$_x$O using photoemission and x-ray absorption spectroscopy, revealing Co$^{2+}$ states and implications for ferromagnetic properties.

Contribution

It provides detailed spectroscopic analysis showing Co ions are divalent and clarifies their electronic states in Zn$_{1-x}$Co$_x$O, impacting the understanding of its magnetic properties.

Findings

Co 3d states are near the top of the O 2p valence band.

Co ions are in the divalent Co$^{2+}$ state under tetrahedral symmetry.

Properly substituted Co ions do not produce diluted ferromagnetic semiconductor behavior.

Abstract

Electronic structures of Zn$_{1-x}$Co$_x$O have been investigated using photoemission spectroscopy (PES) and x-ray absorption spectroscopy (XAS). The Co 3d states are found to lie near the top of the O $2p$ valence band, with a peak around $\sim 3$ eV binding energy. The Co $2p$ XAS spectrum provides evidence that the Co ions in Zn$_{1-x}$Co$_{x}$O are in the divalent Co$^{2+}$ ($d^7$) states under the tetrahedral symmetry. Our finding indicates that the properly substituted Co ions for Zn sites will not produce the diluted ferromagnetic semiconductor property.