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Room-temperature ferromagnetic nanotubes controlled by electron or hole doping


Nanotubes and nanowires with both elemental1,2 (carbon or silicon) and multi-element3,4,5 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 charge6,7,8. 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 (VOx), formed by controllable self-assembly11, 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.

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We thank A. Afzali, K.-S. Cho, C. R. Kagan, F. X. Redl and S. Sun for technical advice, C. A. Feild for chemistry insights, P. Y. Zavalij for his expertise in crystal structures, B. Spivak and A. M. Tsvelik for discussions, and R. Ludeke for his contributions. This work is supported in part by the Defense Advanced Research Project Agency (DARPA).

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Correspondence to L. Krusin-Elbaum.

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The authors declare that they have no competing financial interests.

Supplementary information

Supplementary Figure 1

Optical absorption spectrum of as-assembled VOx nanotubes: figure, figure caption and references (PDF 222 kb)

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Figure 1: Vanadium oxide nanotubes ‘self-assembled’ using dodecylamine as a structure-directing templating agent.
Figure 2: Magnetization of VOx nanotubes after hole and electron doping.
Figure 3: A schematic representation of Mott–Hubbard band splitting in VOx nanotubes and a simple unit-cell model of spin textures with and without charge doping.
Figure 4: Spin-gapped magnetic susceptibility of as-assembled VOx nanotubes, containing approximately one spin in each V(1), V(2), and V(3) site.


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