Room-temperature ferromagnetic nanotubes controlled by electron or hole doping

Nanotubes and nanowires with both elemental(,)(1)(2) (carbon or silicon) and multi-element(3-5) compositions (such as compound semiconductors or oxides), and exhibiting electronic properties ranging from metallic to semiconducting, are being extensively investigated for use in device structures designed to control electron charge(6-8). However, another important degree of freedom-electron spin, the control of which underlies the operation of 'spintronic' devices(9)-has been much less explored. This is probably due to the relative paucity of nanometre-scale ferromagnetic building blocks(10) (in which electron spins are naturally aligned) from which spin-polarized electrons can be injected. Here we describe nanotubes of vanadium oxide (VOx), formed by controllable self-assembly(11), that are ferromagnetic at room temperature. The as-formed nanotubes are transformed from spin-frustrated semiconductors to ferromagnets by doping with either electrons or holes, potentially offering a route to spin control(12) in nanotube-based heterostructures(13).