We describe a way of generating films (<2 mm2; <40 μm 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 μm in length. The carbon tubes, which coat the wires, have external diameters of ∼20–70 nm and are <40 μm 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.

We demonstrate that one of the most commonly used criteria to ascertain that tunneling is the dominant conduction mechanism in magnetic tunnel junctions-fits of current-voltage (I-V) data-is far from reliable. Using a superconducting electrode and measuring the differential conductance below T c , we divide samples into junctions with an integral barrier and junctions having metallic shorts through the barrier. Despite the clear difference in barrier quality, equally reasonable fits to the I-V data are obtained above T c. Our results further suggest that the temperature dependence of the zero-bias resistance is a more solid criterion, which could therefore be used to rule out possible pinholes in the barrier.

Point contact and tunnelling experiments performed at low temperatures were used to study the electronic behaviour of the icosahedral quasicrystalline alloys AlPdRe, AlCuFe, and AlPdMn. With samples of high quality we observed at low temperatures a zero-bias anomaly that we related to the decrease of the electronic density of states (DOS) due to the electron-electron interaction. This interaction tends to diminish the DOS at the Fermi level and can be seen as the energy pseudogap of the alloy. Our experiments indicate that the DOS is strongly modified near and consists of a spiky feature in a broad pseudogap, with the width of the feature of the order of 100 meV or even larger for the AlPdRe, whereas it is as small as 20-22 meV for Al-Cu-Fe and 17-20 meV for Al-Pd-Mn. The broad pseudogap has widths larger than 400 meV for AlPdRe, whereas for AlCuFe it is about 80-90 meV and for AlPdMn it is of the order of 110-122 meV. The studies were performed on three samples of the compositions , , and . The junctions were of the types alloy-Au(In, Al) and alloy-insulator-Au(In, Al), and were studied at different temperatures between that of liquid nitrogen and 2 K, and even to 400 mK for the AlCuFe alloy.

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