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تسجيل مستخدم جديدFerromagnetic, structurally disordered ZnO implanted with Co ions
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We present superparamagnetic clusters of structurally highly disordered Co-Zn-O created by high fluence Co ion implantation into ZnO (0001) single crystals at low temperatures. This secondary phase cannot be detected by common x-ray diffraction but is observed by high-resolution transmission electron microscopy. In contrast to many other secondary phases in a ZnO matrix it induces low-field anomalous Hall effect and thus is a candidate for magneto-electronics applications.
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We have studied the structural, magnetic and electronic properties of Co-implanted ZnO (0001) films grown on Al2O3 (1120) substrates for different implantation doses and over a wide temperature range. Strong room temperature ferromagnetism is observe
d with magnetic parameters depending on the cobalt implantation dose. A detailed analysis of the structural and magnetic properties indicates that there are two magnetic phases in Co-implanted ZnO films. One is a ferromagnetic phase due to the formation of long range ferromagnetic ordering between implanted magnetic cobalt ions in the ZnO layer, the second one is a superparamagnetic phase, which occurs due to the formation of metallic cobalt clusters in the Al2O3 substrate. Using x-ray resonant magnetic scattering, the element specific magnetization of cobalt, oxygen and Zn was investigated. Magnetic dichroism was observed at the Co L2,3 edges as well as at the O K edge. In addition, the anomalous Hall effect is also observed, supporting the intrinsic nature of ferromagnetism in Co-implanted ZnO films.
Unexpected ferromagnetism has been observed in carbon doped ZnO films grown by pulsed laser deposition [Phys. Rev. Lett. 99, 127201 (2007)]. In this letter, we introduce carbon into ZnO films by ion implantation. Room temperature ferromagnetism has b
een observed. Our analysis demonstrates that (1) C-doped ferromagnetic ZnO can be achieved by an alternative method, i.e. ion implantation, and (2) the chemical involvement of carbon in the ferromagnetism is indirectly proven.
We have studied the electronic structure and the magnetism of Cu-doped ZnO nanowires, which have been reported to show ferromagnetism at room temperature [G. Z. Xing ${et}$ ${al}$., Adv. Mater. {bf 20}, 3521 (2008).], by x-ray photoemission spectrosc
opy (XPS), x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD). From the XPS and XAS results, we find that the Cu atoms are in the Cu$^{3+}$ state with mixture of Cu$^{2+}$ in the bulk region ($sim$ 100 nm), and that Cu$^{3+}$ ions are dominant in the surface region ($sim$ 5 nm), i.e., the surface electronic structure of the surface region differs from the bulk one. From the magnetic field and temperature dependences of the XMCD intensity, we conclude that the ferromagnetic interaction in ZnO:Cu NWs comes from the Cu$^{2+}$ and Cu$^{3+}$ states in the bulk region, and that most of the doped Cu ions are magnetically inactive probably because they are antiferromagnetically coupled with each other.
We simulated and experimentally investigated the sputter yield of ZnO and GaAs nanowires, which were implanted with energetic Mn ions at room temperature. The resulting thinning of the nanowires and the dopant concentration with increasing Mn ion flu
ency were measured by accurate scanning electron microscopy (SEM) and nano-X-Ray Fluorescence (nanoXRF) quantification, respectively. We observed a clear enhanced sputter yield for the irradiated nanowires compared to bulk, which is also corroborated by iradina simulations. These show a maximum if the ion range matches the nanowire diameter. As a consequence of the erosion thinning of the nanowire, the incorporation of the Mn dopants is also enhanced and increases non-linearly with increasing ion fluency.
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