Tracking spin-glass barriers versus field and temperature in $a{\text{-Gd}}_{0.19}{\text{Si}}_{0.81}$

Detailed signatures of the states of the low-temperature spin-glass phase in $a\text{-GdSi}$ films were followed using resistance fluctuations. Two-state switches between different spin-glass configurations were unambiguously identified by the field dependences of the occupation ratios of the states. The temperature dependences of the rates and occupation ratios were tracked in order to determine thermodynamic parameters of the switchers and the temperature dependences of barriers. A reasonable distribution of energy and entropy differences between states was found. Most importantly, the kinetic barriers were found to show no sign of divergence with lowering temperature, contrary to expectations based on prior theoretical and experimental works.

Figure 1

(Color online) Temperature dependence of (a) noise power $S_R\left(f\right)$ integrated over the frequency range of $0.59<f<10.38\text{Hz}$, inset: $R$ vs $T$ of the bridge arm including a small constriction. (b) Noise spectral slope $\alpha$ (see text for definition) and (c) magnetic susceptibility measured at 4 Oe and 135 Hz.

Figure 2

(Color online) Noise power, from 1.3 to 27.1 Hz, versus temperature at different magnetic fields. Each panel compares $H=0$ and $H>0$ results. Data were taken on cooling with in-plane field orientation at $dT/dt\sim 0.2\text{K}/\text{min}$. The inset shows the temperature at which the power crosses an arbitrary threshold, 1.5 in these units. Error bars on the $H=4\text{T}$ point extend to $T=0$.

Figure 3

(Color online) Imbalance voltage of an individual switcher at several temperatures.

Figure 4

(Color online) The characteristic net switching time and the natural logarithmic of the ratio of the times spent in the two states are shown as a function of inverse temperature for two different switchers along with inferred kinetic and thermodynamic parameters, as described in the text. Open symbols show data taken on return to the initial $T$.

Figure 5

(Color online) The characteristic times spent in each state and the ratios of those times are shown as functions of the applied magnetic field along with the inferred moment differences between the two states. Open symbols show points taken on return to $H=0$.