Regensburg 2007 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 20: Correlated Electrons - Poster Session
TT 20.33: Poster
Wednesday, March 28, 2007, 14:00–17:45, Poster A
Electrochemical doping of Vanadium Oxide Nanotubes — •A. Popa1, I. Hellmann1, R. Klingeler1, V. Kataev1, E. Vavilova1,2, Y. Arango1, C. Täschner1, X. Liu1, M. Knupfer1, C. Masquelier3, and B. Büchner1 — 1Leibniz-Institute for Solid State and Materials Research IFW Dresden, Dresden, Germany — 2Kazan Physical Technical Institute, RAS, Kazan, Russia — 3Laboratoire de Réactivité et de Chimie des Solides, Amiens, France
Vanadium oxide nanotubes (VOx-NTs) exhibit diverse properties ranging from spin frustration and
semiconductivity to ferromagnetism by doping with either electrons or holes [1]. We have applied
optical, photoemission and EELS as well as static magnetization, ESR
and NMR studies in order to obtain insight into the rich physics of these materials. Our data suggest an averaged vanadium valency of about 4.4+ in the undoped case [2]. We
observe two magnetically nonequivalent vanadium sites, attributed to
V4+ ions (3d1, S=1/2) in octahedral and tetrahedral oxygen coordination and there are strong indications that antiferromagnetic
dimers and trimers occur in the vanadium-spin chains in the walls. We
find a spin gap of the order of 700 K [3]. Upon electron doping of VOx-NTs, our spectroscopic data
confirm a higher number of magnetic V4+ sites. Besides, the magnetic response was studied after the electrochemical insertion of lithium. For certain doping
levels, a ferromagnetic signal at room temperature was found.
[1] L. Krusin-Elbaum et al., Nature 431, 672 (2004)
[2] X. Liu et al., Phys. Rev. B 72, 115407 (2005)
[3] E. Vavilova et al., Phys Rev. B 73, 144417 (2006)