Magnetic properties of double-layer vanadium oxides and vanadium oxide nanotubes.

Double-layer V$_{8}$O$_{20}$ compounds\footnote{ P. Y. Zavalij and M. S. Whittingham, Acta Cryst. B55, 627 (1999).} intercalated with various cations and the vanadium oxide nanotubes (VONTs) VO$_{2.4}$[C$_{12}$H$_{28}$N]$_{0.31}\cdot $0.56H$_{2}$O were prepared using hydrothermal method and characterized by x-ray diffraction, TGA, TEM, FTIR. Magnetic properties were studied using SQUID magnetometer. Depending on the intercalated cation type, the magnetic susceptibility of V$_{8}$O$_{20}$ compounds reveal presence of small clusters or infinite linear chains with antiferromagnetic (AF) exchange. VONTs show a spin gap, which is well described by the simple model of magnetic dimers with AF exchange. Various ion exchange and red-ox reactions are performed on VONTs. Structure and magnetic properties of the resulting compounds are discussed. No ferromagnetic response from the VONTs reacted with BuLi is found\footnote{ L. Krusin-Elbaum, D. M. Newns, H. Zeng, V. Derycke, J. Z. Sun and R. Sandstrom, Nature 431, 627 (2004).}. The work is supported by the National Science Foundation through grant DMR 0313963.