Extraordinary Hall-Effect Measurements on Ni, Some Ni Alloys, and Ferrites

Extraordinary Hall-effect measurements over a wide range of temperature are reported for 99.9 Ni, 99.4 Ni, 95 Ni, several 80% Ni alloys, Fe₃{O}₄$, and ${(NiO)}0.75$ ${(FeO)}0.25$ (${Fe}₂O₃). The resistivity ρ of all samples over the same temperature range is also reported. At high temperatures, the extraordinary Hall coefficient R₁ for 99.9 Ni is proportional to ρ² as predicted by theory. However, the dependence upon ρ is smaller in the 99.9 Ni sample at lower temperatures and in the samples with higher impurity concentration at all temperatures. The 80% Ni samples exhibit positive R₁, while R₁ in the high-concentration Ni samples is negative. R₁ for both ferrites is negative below about 400^∘{}C and positive above this temperature.The theoretical work on metals generally indicates that R₁ is proportional to ρ² and the constant of proportionality r is weakly temperature dependent and of the order of unity. In the high-concentration Ni samples r is negative, of the order of unity, and exhibits a significant temperature dependence at low temperatures. In the 80% Ni samples, r is positive and of the order of 10^-2. At room temperature, r is of the order of 10^-3 in Fe₃{O}₄$ and of the order of ${10}^{{-}6}$ in ${(NiO)}0.75$ ${(FeO)}0.25$ (${Fe}₂O₃). In both ferrites, r is strongly temperature dependent. The change of sign of r with temperature observed in both ferrites has not been previously observed in metals or alloys.