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Lu Z.L.,Nanjing Southeast University | Lu Z.L.,National Cheng Kung University | Bian X.F.,Nanjing Southeast University | Zou W.Q.,Jiangsu Provincial Laboratory for Nanotechnology | And 2 more authors.
Journal of Alloys and Compounds | Year: 2010

High-quality Zn 0.95Co 0.05O single crystalline films have been grown on a-plane sapphire substrates using molecular-beam epitaxy. The as-grown films show high resistivity and non-ferromagnetism at room temperature, and they become good conductive and ferromagnetic after annealing in Ar atmosphere or Ar(95%)/H 2(5%) mixed-gas. Compared with weak ferromagnetism (0.16 μ B/Co) in the Zn 0.95Co 0.05O film annealed in pure Ar atmosphere, the film annealed in the Ar/H 2 mixed-gas shows much stronger ferromagnetism (0.82 μ B/Co) at room temperature. For all of the samples, both of the X-ray diffraction and optical transmission spectrum analyses suggest the incorporation of Co 2+ cations into wurtzite ZnO lattice. However, X-ray absorption studies based on synchronization radiation clearly indicate the presence of metallic Co clusters in the Zn 0.95Co 0.05O film upon thermal annealing in Ar/H 2 mixed-gas. Our work demonstrates that minor ferromagnetic phases below the detection limit of conventional characterization techniques may exist in the transition-metal doped ZnO films, especially grown and/or annealed in the reducing atmosphere, and be responsible for the observed ferromagnetism. © 2009 Elsevier B.V. All rights reserved. Source


Zhao C.,Nanjing University | Zhao C.,Jiangsu Provincial Laboratory for Nanotechnology | Tang S.L.,Nanjing University | Tang S.L.,Jiangsu Provincial Laboratory for Nanotechnology | And 2 more authors.
Chemical Physics Letters | Year: 2010

Surface plasmon excitation using resonant metal nanowires in Anodized Aluminum Oxide is studied experimentally. Absorption spectra measurement reveals the existence of broad-band plasmon resonances. Besides the regular resonances of ideal nanowire and plasmon coupling, effect of nanowire's geometry is evident for absorption in irregular wavelength. This is ascribed to the pores without widening, resulting in not straight nanowires. Nanowire arrays with other diameters and interpore distances and Y-junction nanostructures are investigated to confirm this model. These findings are important for applications utilizing plasmon resonance of nanostructures. © 2010 Elsevier B.V. All rights reserved. Source


Tang G.,Nanjing University | Tang G.,Jiangsu Provincial Laboratory for Nanotechnology | Tang C.,Nanjing University | Xu X.,Nanjing University | And 6 more authors.
Solid State Communications | Year: 2010

The magnetothermopower have been studied in Lu-doped Ca 3-xLuxCo4O9+δ. A strong magnetic field suppression of thermopower indicates large spin entropy contribution. The magnetothermopower for doped samples are overall enhanced compared with that for undoped Ca3Co4O 9+δ, providing an experimental evidence for the enhancement of spin entropy. Magnetic results confirm that Co4+ concentration is reduced by Lu doping. We suggest that the reduction in Co4+ concentration results in the enhanced spin entropy. © 2010 Elsevier Ltd. All rights reserved. Source


Tang G.D.,Nanjing University | Tang G.D.,Jiangsu Provincial Laboratory for Nanotechnology | Xu X.N.,Nanjing University | Tang C.P.,Nanjing University | And 5 more authors.
Journal of Applied Physics | Year: 2010

Through the measurements of magnetothermopower on NaCo2-x Fex O4, we find that the spin entropy is suppressed by doping with high-spin Fe3+ (S=5/2) which is revealed by Mössbauer spectra. The Mössbauer spectra and magnetic properties indicate that the Co4+ concentration is enhanced by Fe doping. A suitable theoretical model is adopted to explain commendably the spin entropy suppression. © 2010 American Institute of Physics. Source


Zhang D.W.,Nanjing University | Zhang D.W.,Jiangsu Provincial Laboratory for Nanotechnology | Tang G.D.,Nanjing University of Science and Technology | Xu X.B.,Nanjing University | And 4 more authors.
Modern Physics Letters B | Year: 2012

We have investigated the chemical pressure effects, induced by the substitution of smaller ionic radius Y 3+ for La 3+, on the magnetic and electrical transport properties for the La 0.7-xY xCa 0.3CoO 3 (x = 0, 0.05, 0.1, and 0.15). The magnetization and the Curie temperature T C decrease sharply as the doping level of Y 3+ increases, which indicates that the chemical pressure induced by Y 3+-doping can suppress the ferromagnetism. The transport measurement reveals a chemical pressure-induced increase of the resistivity due to a suppression of e g-electron hopping. We thought that the effect of Y 3+-doping induced chemical pressure on the ferromagnetic (FM) phase has a similar behavior to that of external pressure. These results imply that the enhancing chemical pressure can suppress the FM phase in La 0.7-xY xCa 0.3CoO 3. © 2012 World Scientific Publishing Company. Source

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