The magnetization reversal process of single Co nanowires is investigated experimentally by magnetoresistance measurements at low temperatures. The results are compared to magnetic force micrographs of the remanent domain configuration. The theoretical expectation for the reversal process is obtained from Monte Carlo simulations. We find that both the width and the thickness of the wires as well as surface scattering play a significant role for the magnetization reversal processes. While thick ͑t Ͼ 15 nm͒ and narrow nanowires ͑w Ͻ 800 nm͒ switch by domain wall nucleation at the wire ends followed by wall motion, the magnetization reversal process in wide and/or thin nanowires is achieved by the generation of a multidomain state of the magnetization. It is shown both experimentally as well as theoretically that the wire width dependence of the coercive field can be used to pin a domain wall between two wire parts of different widths.

We have investigated the low temperature resistance behavior and the magnetoresistance of single-domain cobalt nanowires of various thicknesses ranging between 5 nm and 32 nm and wire widths ranging down to 32 nm. The nanowires are coated with insulating carbon on three sides to prevent oxidation. Magnetic force microscopy investigations show that nanowires with widths below 800 nm are in a single-domain-like remanence state. The magnetoresistance is negative and is well explained by the anisotropic magnetoresistance ͑AMR͒. At low temperatures T Ͻ 30 K a logarithmic resistance increase is observed with decreasing temperature, which is consistently explained as originating from enhanced electron-electron interactions in two dimensions. Quantum corrections due to weak electron localization are not observed which is in contrast to recent theoretical predictions for two-dimensional ferromagnetic systems. However, the results are consistent with our earlier results obtained for platinum-capped and unprotected cobalt nanowires. A reduction of the wire width below about 400 nm yields a crossover behavior from two-dimensional to one-dimensional behavior with respect to the quantum corrections of the resistance.

Single (Co/Pt)_{7} multilayer nanowires prepared by electron beam lithography with perpendicular magnetic anisotropy are locally modified by means of Ga-ion implantation generating 180 degrees domain walls which are pinned at the edges of underlying thin Pt wires. Since we can exclude contributions from the anisotropic and the Lorentz magnetoresistance this allows us to determine the resistance of a single domain wall at room temperature. We find a positive relative resistance increase of DeltaR/R=1.8% inside the domain wall which agrees well with the model of Levy and Zhang [Phys. Rev. Lett. 79, 5110 (1997)10.1103/PhysRevLett.79.5110].

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We report on low temperature resistance and magnetoresistance (MR) measurements for various (Co/Pt)nmultilayer-nanowires with perpendicular magnetic anisotropy and different widths, designed as model systems for the experimental observation of weak electron localization effects in ferromagnetic systems as proposed by Dugaev et al. [Phys. Rev. B 64, 144423 (2001)]. The low temperature MR is found to originate from both the anisotropic MR and domain wall scattering. The temperature dependence of the resistance shows a logarithmic resistance increase with decreasing temperature, as it is typical for quantum corrections in two dimensional systems. Upon application of a perpendicular magnetic field, however, the slope of the logarithmic resistance increase does not change in magnitude, which proofs that weak localization effects are not present, at least within the accuracy of our measurements. Instead, the observed quantum corrections of the resistance are well explained by enhanced electron-electron interaction effects in two dimensions. The results are discussed with regard to recent experimental as well as theoretical works.