ASYMMETRIC NONLINEAR DIFFERENTIAL RESISTANCE OF MESOSCOPIC AUFE SPIN-GLASS WIRES

We have measured the differential resistance R = dV/dI of mesoscopic A uFe wires as a function of temperature T and dc current bias I. R(T) s hows a maximum at a temperature T-m similar to 1-4 K, consistent with the onset of spin-glass order in these films. At temperatures T < T-m, R(I) also shows a maximum; however, R(I) is asymmetric in I, the asym metry increasing with decreasing temperature. The asymmetry is sample specific, sensitive to the four terminal measurement configuration, an d is associated with the presence of magnetic impurities in the sample s.