Investigation of the spin exchange interactions in the nanotube system Na2V3O7 by spin dimer analysis

The relative magnitudes of the spin exchange interactions expected for the nanotubes of Na2V3O7 were examined by identifying the spin dimers of the nanotube and calculating their spin orbital interaction energies. Our analysis indicates that the spin exchange interactions of the nanotube are not described by three-legged ladders, but by six mutually intersecting helical chains, and the magnetic properties of the nanotube in the low temperature region can be well approximated by those of a single helical chain. Each helical chain is described by four antiferromagnetc spin exchange parameters J1–J4 with the repeat sequence [–J2–J1–J3–J4–]∞, where |J1|>|J2|>|J3|>|J4|. The nanotube is expected to have a spin gap.