Paramagnetism of the Co sublattice in ferromagnetic Zn${}_{1-x}$Co${}_x$O films

Abstract

Using the spectroscopies based upon x-ray absorption, we have studied the structural and magnetic properties of Zn${}_{1-x}$Co${}_x$O films ($x$ = 0.1 and 0.25) produced by reactive magnetron sputtering. These films show ferromagnetism with a Curie temperature $T_{\mathrm{C}}$ above room temperature in bulk magnetization measurements. Our results show that the Co atoms are in a divalent state and in tetrahedral coordination, thus substituting Zn in the wurtzite-type structure of ZnO. However, x-ray magnetic circular dichroism at the Co \textit{L}${}_{2,3}$ edges reveals that the Co 3\textit{d} sublattice is paramagnetic at all temperatures down to 2 K, both at the surface and in the bulk of the films. The Co 3\textit{d} magnetic moment at room temperature is considerably smaller than that inferred from bulk magnetisation measurements, suggesting that the Co 3\textit{d} electrons are not directly at the origin of the observed ferromagnetism.

5 pages, 5 figures

References in corpus (5)

• Ferromagnetism in substituted zinc oxide
• A possible path to a new class of ferromagnetic and half metallic ferromagnetic materials
• High Curie temperature GaMnAs obtained by resistance-monitored annealing
• Magnetic oxide semiconductors
• Characterization of Magnetic Components in the Diluted Magnetic Semiconductor Zn${}_{1-x}$Co${}_x$O by X-ray Magnetic Circular Dichroism

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• Full control of Co valence in isopolar LaCoO3 / LaTiO3 perovskite heterostructures via interfacial engineering
• Grain boundary ferromagnetism in vanadium-doped In${}_2$O${}_3$ thin films
• Reduction of conductivity and ferromagnetism induced by Ag doping in ZnO:Co