Enhanced magnetic coercivities in Fe nanowires

We describe a way of generating films (< 2 mm(2); < 40 mu m thick) of aligned Fe-filled carbon nanotubes. These Fe nanowires are usually composed of single Fe crystals, and have dimensions from 5-40 nm outer diameter and < 10 mu m in length. The carbon tubes, which coat the wires, have external diameters of similar to 20-70 nm and are < 40 mu m in length. High-resolution electron energy loss spectroscopy, x-ray powder diffraction, and elemental mapping of the tubular structures reveal only characteristic metallic signals and the effective absence of oxygen (or any other nonmetallic element) within the wires. The material exhibits coercivities in the 430-1070 Oe range, i.e., greater than those reported for Ni and Co nanowires. (C) 1999 American Institute of Physics. [S0003-6951(99)00247-8].