X-Ray Spectroscopic Investigations of Zn$_{0.94}$Co$_{0.06}$O Thin Films

Abstract

We investigated Zn 0 94 Co 0 06 O thin films on sapphire (0001) substrates with respect to their structural and magnetic properties. X-ray diffraction shows a axis oriented growth and no secondary phases within its resolution. A clear improvement of the crystalline quality was obtained by post annealing under vacuum conditions. Further information about the local electronic structure is obtained by X-ray absorption spectroscopy at the Co 2 3 and the O edge. Magnetic properties were investigated with a superconducting quantum interference device (SQUID) and by X-ray magnetic circular dichroism at the Co 2 3 edge. Both techniques yield mainly paramagnetic behavior of the samples. For low temperatures, an additional small ferromagnetic contribution was observed in SQUID measurements. Several possible origins of this ferromagnetic contribution are discussed.

Magnetization study of nanograined pure and Mn-doped ZnO films: Formation of a ferromagnetic grain-boundary foam

“…Thus, the presence of Mn ͑or Co͒ is not necessary for the ferromagnetic properties of ZnO. 22,69 Even pure ZnO can be ferromagnetic, critical is the low grain size ͑high s GB ͒, and not the doping with magnetic atoms as it was originally supposed. Nevertheless, the presence of Mn or Co in the ZnO lattice facilitates the transition into ferromagnetic state for ZnO and shifts the threshold s GB toward the larger grain size.…”