Abstract
Magnetic oxide semiconductors with wide band gaps have promising spintronic applications, especially in the case of magneto-optic devices. Co-doped ZnO (ZnCoO) has been considered for these applications, but the origin of its ferromagnetism has been controversial for several decades and no substantial progress for a practical application has been made to date. In this paper, we present direct evidence of hydrogen-mediated ferromagnetism and spin polarization in the conduction band of ZnCoO. Electron density mapping reveals the formation of Co–H–Co, in agreement with theoretical predictions. Electron spin resonance measurement elucidates the ferromagnetic nature of ZnCoO by the formation of Co–H–Co. We provide evidence from magnetic circular dichroism measurements supporting the hypothesis that Co–H–Co contributes to the spin polarization of the conduction band of hydrogen-doped ZnCoO.
Highlights
Over the past few decades, despite numerous theoretical and experimental investigations, the origin of ferromagnetism in Co-doped ZnO (ZnCoO) has remained a mystery
To exclude the effects of secondary phases that might cause ferromagnetism-related features, we carried out careful structural analysis employing synchrotron radiation x-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) experiments
As the hydrogen content increases, MR gradually increases. This demonstrates that the evolution of ferromagnetism correlates with the amount of hydrogen in the sample
Summary
Over the past few decades, despite numerous theoretical and experimental investigations, the origin of ferromagnetism in Co-doped ZnO (ZnCoO) has remained a mystery. Researchers attempted to explain the ferromagnetism and spin-dependent phenomena observed in ZnCoO in terms of magnetic clusters[1,2,3,4], carrier mediation[5, 6], or magnetic polarons based on intrinsic defects[7,8,9] None of these can clearly explain the inconsistent results reported. The results of electron spin resonance (ESR) measurement support the hypothesis that the antiferromagnetic ordering of nearest-neighbored Co–Co is converted into a ferromagnetic ordering by the formation of Co–H–Co. Magnetic circular dichroism measurements reveal the evolution of the spin-polarized conduction band correlated with the hydrogen content. The results of structural analyses with synchrotron XRD, X-ray absorption spectroscopy (XAS), and transmission electron microscopy (TEM) exclude other possible extrinsic sources of ferromagnetism and spin-dependent band structures in ZnCoO
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