Hall effect in a three-dimensional percolation system

We have studied the Hall effect in random mixtures of Al-Ge. The observed variation of the Hall coefficient over a wide range of concentration was found to be in full agreement with recent theoretical predictions for three-dimensional percolation systems. For the first time the critical behavior was studied near both percolation thresholds, namely, near the critical-volume concentrations of Al and of Ge. We observed a strong divergence of the Hall coefficient with exponent 3.8 0.2 near the threshold of Al, and a much slower divergence with exponent 0.38 0.05 close to the threshold of Ge.