Electronic structure of Cu-doped ZnO thin films by x-ray absorption, magnetic circular dichroism, and resonant inelastic x-ray scattering

Abstract

The electronic structure of Cu-doped ZnO thin films, synthesized with a nominal composition of Zn1−xCuxO (x=0.03, 0.05, 0.07, and 0.10) by using spray pyrolysis method, has been investigated using near-edge x-ray absorption fine structure (NEXAFS) experiments at the O K- and the Cu L3,2-edges and resonant inelastic x-ray scattering (RIXS) measurements at Cu L3,2 edge. The Zn1−xCuxO thin films showed single phase wurtzite-hexagonal like crystal structure and ferromagnetic behavior at room temperature (RT). The intensity of the pre-edge spectral feature at the O K-edge increases with the Cu concentration, which clearly reveals that there is strong hybridization of O 2p–Cu 3d orbitals in the ZnO matrix. Spectral features of the Cu L3,2-edge NEXAFS exhibit multiple absorption peaks and appreciable x-ray magnetic circular dichroism signal that persists even at RT. These results demonstrate that Cu is in mixed valence state of Cu2+,3+/Cu1+, substituting at the Zn site and Cu2+/3+ ions are magnetically polarized. RIXS experiments at Cu L3 edge show strong d-d excitations due to localized nature of Cu ions in the ZnO matrix.

Co-Precipitation Synthesis and Characterization of Nanocrystalline Zinc Oxide Particles Doped with Cu<sup>2+</sup> Ions

“…Since Cu and related oxides are nonmagnetic materials at room temperature, the observed ferromagnetism is thought to be intrinsic properties of the Cu-doped ZnO [34]. A similar result was also found by Sharma et al [35].…”

Cu- and Ni-Doping Effect on Structure and Magnetic Properties of Fe-Doped ZnO Nanoparticles

“…Thus, it is useful to consider all possible ferromagnetic impurity phases that might be present in both samples. It is known that Cu-related oxides such as CuO, Cu 2 O or Cu clustering could not contribute to the room temperature ferromagnetism, because none of them exhibit ferromagnetism above room temperature [54][55][56]. Therefore the ferromagnetism behavior observed in our Cu-doped samples studied here does not seem to be related with the presence of any secondary phases or Cu clusters, while Cu clusters and its oxides are generally considered to be non-ferromagnetic and could not contribute to the room temperature ferromagnetic.…”

Multi-roles of Cu ions in the ferromagnetic properties of (Cu, Al)-codoped ZnO thin films

“…Although room-temperature ferromagnetism in Cu-doped ZnO system has been reported, the ferromagnetic mechanism still remains controversial [13,14]. It is still an issue whether the ferromagnetism observed in experiments is mediated by defects or induced by carriers [15,16].…”