Dresden 2006 – wissenschaftliches Programm
Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe
TT: Tiefe Temperaturen
TT 25: Correlated Electrons - Poster Session
TT 25.18: Poster
Mittwoch, 29. März 2006, 14:30–18:30, P1
51V NMR Study of Vanadium Oxide Nanotubes — •E. Vavilova1,2, V. Kataev1, I. Hellmann1, R. Klingeler1, C. Täschner1, and B. Büchner1 — 1Leibniz Institute for Solid State and Materials Research IFW Dresden, D-01171 Dresden, Germany — 2Kazan Physical Technical Institute, RAS, 420029 Kazan, Russia
Mixed valent vanadium oxide nanotubes VOx-NT have recently attracted much attention as they exhibit a number of unusual magnetic properties, ranging from ferromagnetism at room temperature to spin-liquid phenomena [1]. In these nanoscale magnets one finds structurally well defined V-O-V-... chains, but also isolated V-sites. In order to get an insight into the spin dynamics of this complex system we performed NMR measurements on 51V nuclei in a magnetic field of 7.05 T at temperatures between 15 K and 285 K. We find a broad NMR spectrum centered at a frequency ∼ 78.9 MHz with a partially relsoved quadrupole structure. Measurements of transversal and longitudinal nuclear-spin relaxation times, T2 and T1, respectively, reveal two sites of V with distinctly different relaxation rates. These two sites are assigned to vanadium in 4+ (d1, S = 1/2) and 5+ (d0, S = 0) oxidation states, respectively. Though T1 at both sites exhibit a strong temperature dependence we find no evidence for a spin gap of the order ∼ 700 K which possible occurrence in VOx-NT is suggested in Ref. [1]. In addition to NMR results we present also our magnetization data and discuss possible mechanisms of vanadium nuclear spin relaxation and their interplay with the static magnetic properties.