Electrical noise from spins inFe1−xZrx

In films of a-${\mathrm{Fe}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Zr}}_{\mathit{x}}$ with x≊0.08 two distinct transitions were found in the electrical noise. A high-temperature transition produced a regime of strongly magnetic-field-dependent noise showing non-Gaussian effects, as would be expected at the ferromagnetic transition. Observations of single-domain switching events give a direct estimate of a dynamical coherence length, large enough to show true ferromagnetism in the films. At lower temperature, a sharp, field-dependent rise in noise appeared near the suspected spin-glass transition, as in other conducting spin glasses. The temperature and frequency dependences of the noise at the lower transition imply cooperativity.