Significance of Hall-Effect Measurements in Very Dilute Alloys

Abstract

The Hall coefficients of some samples of high-purity polycrystalline $\mathrm{I}B$ metals are found to be fieldindependent when measured in the high-field condition. This is contrary to expectations expressed in the literature. It is shown that the presence of trace impurities can cause an apparent field dependence of the Hall coefficient, which is presumably what previous workers have observed, but which is not a fundamental property of the pure metal; it is caused by the transition between the high- and low-field conditions during the experiment. The work has involved measurements of the Hall coefficients at 4.2°K of alloys of the $\mathrm{I}B$ metals with controlled trace amounts of Zn, Mn, or Fe impurities. From measurements on doped-Cu single crystals, an empirical criterion for the low-field-high-field transition in the $\mathrm{Cu}$-Zn system at 4.2°K is established which can presumably be extended to analogous systems. It is shown, using this criterion, that the anomalous temperature dependence of the Hall coefficients of the pure $\mathrm{I}B$ metals seen at about 50°K is definitely not the result of a low-field-high-field transition. The proposed explanations of this anomaly are reexamined in the light of these results.