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Recently we reported on the differential resistance R(I) = dV/dI of narrow AuFe spin-glass wires (Phys. Rev. Let., 77 (1996) 2276). Surprisingly, R(I) was found to be asymmetric in I for the smallest samples. In this letter we present differential resistance measurements performed on a AuFe wire with a multiprobe geometry. The new experiments reveal that the asymmetric behavior of R(I) can be explained in terms of a mesoscopic thermoelectric effect. Our experiments also indicate that the thermopower S of a AuFe spin-glass alloy becomes size dependent for length scales below a few hundred nanometers.

We have studied fluxoid quantization effects in mesoscopic Al samples consisting of a small number of square loops. In short microladders a pronounced substructure of the Little-Parks oscillations (i.e. the oscillations of the critical temperature Tc as a function of the applied magnetic flux Φ) has been found. These new features in Tc(Φ) originate from transitions between different quantum states, each having a specific order parameter profile and flow pattern of the supercurrents. The experimental data are in excellent agreement with the Tc(Φ) calculated within the de Gennes-Alexander model for superconducting micronetworks.

We report on the low-temperature resistivity ρ(T) of AuFe spin-glass wires with a thickness around 20 nm and a linewidth varying between 300 μm and 150 nm. The observed linewidth dependence of ρ(T) is due to the contribution of the disorder-enhanced electron-electron interaction, while the spin-glass contribution is independent of linewidth. However, a quantitative analysis of the ρ(T) data reveals a substantial suppression of both the amplitude of the spin-glass resistivity and the interaction strength between magnetic impurities when compared to bulk AuFe alloys. This may indicate the presence of a size effect resulting from the finite spin-glass thickness.