Ferromagnetism in ZnO:Co originating from a hydrogenated Co-O-Co complex

Formation of ferromagnetic Co-H-Co complex and spin-polarized conduction band in Co-doped ZnO

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.

A New Theoretical Insight Into ZnO NWs Memristive Behavior

Resistive switching memory operation is generally described in terms of formation and rupture of a conductive filament connecting two metal electrodes. Although this model was reported for several device types, its applicability is not guaranteed to all of them. On the basis of density functional theory calculations, we propose a novel switching mechanism suitable to nanowire-based resistive switching memories. For thick devices in particular, the current is highly unlikely to flow through a metallic filament connecting the electrodes. We demonstrate that in the case of ZnO nanowires metal adatoms, spread on the nanowire surface, locally dope the insulating oxide allowing surface conductance even for small metal concentrations.