Manipulating the spin rather than the charge of the electron is one of the approaches being explored to develop future generations of semiconductor devices. ‘Spintronic’ devices could replace their electronic counterparts as feature sizes continue to shrink and quantum effects disrupt the operation of conventional submicrometre semiconductor devices.

Several devices, such as giant magnetoresistive sensors, already rely on the manipulation of electron spin in multilayered magnetic structures for their operation. In comparison with semiconductor electronics, these devices offer the advantages of non-volatility, lower power consumption and higher integration density.

Nanoscale systems exhibiting both semiconducting and ferromagnetic properties would enable both charges and spins to be exploited in devices. Single-walled carbon nanotubes containing magnetic particles should exhibit both properties, but it has proved difficult to get the magnetic particles into the nanotubes.

Yongfeng Li and colleagues at Tohoku University in Japan have now devised a simple two-step method for doing this. The nanotubes are placed into a glass ampoule with ferrocene (Fe(C5H5)2) powder, and the ampoule is then evacuated, sealed and heated at 180 °C for two days. The system is then annealed at 700 °C to release the iron atoms into the nanotubes. Measurements of the physical properties of the iron-filled nanotubes are now in progress.