Universal conductance fluctuations and low-temperature1/fnoise in mesoscopic AuFe spin glasses

Abstract

We report on intrinsic time-dependent conductance fluctuations observed in mesoscopic AuFe spin-glass wires. These dynamical fluctuations have a 1/f -like spectrum and appear below the measured spin-glass freezing temperature of our samples. The dependence of the fluctuation amplitude on temperature, magnetic field, voltage, and Fe concentration allows a consistent interpretation in terms of quantum interference effects, that are sensitive to the slowly fluctuating spin configuration.

Tracking spin-glass barriers versus field and temperature ina-Gd0.19Si0.81

“…Then S R ͑f͒ was measured while slowly cooling the system in constant H. The whole procedure was repeated for different values of H. Larger ͉H͉ generally resulted in lower temperatures for the onset of increased noise, similar to previous results on a standard metallic spin glass. 25 In the range of ͉H͉ Յ 4 T we confirm 14 that the changes in magnetoresistance are well under 1% and hence are irrelevant to the dramatic H dependence of the noise. The decrease in the noise onset T with increase in H roughly resembles theoretical predictions for the field-dependent T g ͑Ref.…”

“…[10][11][12][21][22][23][24][25][26][27] Figures 1͑a͒ and 1͑b͒ show the dependence of S R ͑f͒ and noise-spectral slope ␣ ϵ − ‫ץ‬ ln S R ͑f͒ ‫ץ‬ ln͑f͒ on T. Above T Ϸ 6.5 K we found ordinary 1 / f-like ͑␣ Ϸ 1͒ noise with small temporal variations in the noise power. Around T Ϸ 6.5 K, S R ͑f͒ increases considerably and ␣ reaches its minimum ͑␣ Ϸ 0.5͒.…”

Scaling of1∕fnoise in tunable break junctions

“…1 / f noise has intensively been studied for bulk and thin-film conductors, [9][10][11][12][13][14][15][16][17][18] in particular as a diagnostic tool for the technologically relevant electromigration ͑EM͒ mechanism. [19][20][21][22] Noise at low and high frequencies has also been explored in small constrictions, [23][24][25][26] nanoelectronic devices, 27,28 quantum point contacts, 29 submicron interconnects, 30,31 quantum coherent, quasiballistic and ballistic nanowires, [32][33][34][35][36][37][38][39] and tunneling contacts. 40,41 The power-spectral density of resistance fluctuations S R can phenomenologically be described by Hooge's law, 9,12 …”

Measuring Overlaps in Mesoscopic Spin Glasses via Conductance Fluctuations

“…Parallel to these theoretical developments, experimental measurements of conductance fluctuations in metallic spin glasses by de Vegvar et al [13] (see also [14]) demonstrated for the first time a clear signature of the spin glass freezing in the time-reversal antisymmetric part of the four terminal conductance. Later, several experiments focused on noise measurements in Cu:Mn [15] and Au:Fe [16] (see also [17] for similar studies in the doped semiconductor).…”