Coiled carbon nanotubes were produced catalytically by thermal decomposition of hydrocarbon gas. After deposition on a silicon substrate, the three-dimensional structure of the helix-shaped multiwalled nanotubes can be visualized with atomic force microscopy. Helical structures of both chiralities are present in the nanotube deposits. For larger coil diameters ( >170 nm), force modulation microscopy allows one to probe the local elasticity along the length of the coil. Our results agree with the classical theory of elasticity. Similar to the case of straight nanotubes, the Young modulus of coiled multiwalled nanotubes remains comparable to the very high Young modulus of hexagonal graphene sheets.

No abstract

We have performed magnetic force microscopy measurements on isolated 35 nm thick rectangular Co structures. The structures have a length L ranging between 0.25 and 10 μm and a width W ranging between 0.25 and 5.5 μm, covering aspect ratios m=L/W between 1 and 40. This enables us to map the transition from a magnetic single-domain state towards a magnetic multidomain state when increasing the size of the structures. This transition depends on the size as well as the aspect ratio of the structures. Our results can be interpreted in terms of the theoretical model developed by A. Aharoni [J. Appl. Phys. 63, 5879 (1988)].

In order to probe the influence of the surface-induced anisotropy on the impurity spin magnetization, we measure the anomalous Hall effect in thin AuFe films at magnetic fields up to 15 T. The observed suppression of the anomalous Hall resistivity at low fields as well as the appearance of a minimum in the differential Hall resistivity at higher fields can be explained by our theoretical model, which takes into account the influence of a polycrystalline film structure on the surface-induced anisotropy. Our results imply that the apparent discrepancy between different experimental results for the size effects in dilute magnetic alloys can be linked to a different microstructure of the samples.

Articles you may be interested inFormation of single electron transistors in single-walled carbon nanotubes with low energy Ar ion irradiation technique J.