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' devices⁹ - has been much less explored. This is probably due to the relative paucity of nanometre-scale ferromagnetic building blocks¹⁰ (in which electron spins are naturally aligned) from which spin-polarized electrons can be injected. Here we describe nanotubes of vanadium oxide (VO_x), 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 control¹² in nanotube-based heterostructures¹³.