Magnetic properties of vanadium oxide nanorods, nanotubes and nanourchins.

Vanadium oxide nanotubes (VONTs) were prepared by hydrothermal method and ion exchanged with BuLi. Vanadium oxide nanorods were synthesized by hydrothermal treatment of electrospun precursors. The compounds were characterized by x-ray diffraction, TGA, TEM, FTIR and magnetic susceptibility techniques. Magnetic properties of VONTs are found to be similar to that reported earlier [1]. Upon ion exchange with BuLi the amount of isolated V$^{4+}$ is preserved, but the spin-gap behavior becomes less pronounced. No hysteresis of magnetization is found as opposed to earlier report [1]. Vanadium oxide nanourchins have similar structure with VONTs; however, their magnetic properties are different. Vanadium oxide nanorods with the structure related to $\delta $-V$_{4}$O$_{10}$ show a large spin gap of 560 K. The V$^{4+}$ content is around 0.125 in this compound as follows from the analysis of the spin-gap behavior with the dimer model. [1] L. Krusin-Elbaum, D. M. Newns, H. Zeng, V. Derycke, J. Z. Sun and R. Sandstrom, Nature 431, 627 (2004).