The switching of the magnetization of single Ni wires with diameters 40-100 nm was measured at temperatures between 0.13 and 6 K. The angular dependence of the switching field was studied for several wire diameters. Repetitive measurements allow us to obtain histograms of the switching field values. For the smallest diameters, the measurements of the probability of reversal revealed a thermally activated switching following an Arrhenius law with an activation volume much smaller than the volume of the wire.

A new technique is required which enables tailoring of the morphology of a metallic nanostructured material down to the 10 nm length scale. Using nanoporous nuclear track etched membranes as templates for electrodeposition, an assembly of wires with diameters as low as 30 nm could be obtained. Alternating the electrodeposition of two metals resulted in multilayers grown perpendicular to the wire axis. Layer thicknesses as low as 2 nm could be reached. Application is demonstrated by making wires 6 μm long, 80 nm in diameter, having a succession of either Co and Cu layers or of (Ni,Fe) and Cu layers. Wires containing layers of 5–10 nm in thickness exhibited a giant magnetoresistance. The current was naturally perpendicular to the layers. At ambient temperature, a magnetoresistance of 14% for Co/Cu and of 10% for (Fe,Ni)/Cu was observed.

Resonant tunneling via localized states in the barrier can invert magnetoresistance in magnetic tunnel junctions. Experiments performed on electrodeposited $\mathrm{N}\mathrm{i}/\mathrm{N}\mathrm{i}\mathrm{O}/\mathrm{C}\mathrm{o}$ nanojunctions of area smaller than $0.01\mu {\mathrm{m}}^2$ show that both positive and negative values of magnetoresistance are possible. Calculations based on Landauer-Büttiker theory explain this behavior in terms of disorder-driven statistical variations in magnetoresistance with a finite probability of inversion due to resonant tunneling.