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, ${\mathrm{Fe}}_3$ ${\mathrm{O}}_4$, and ${\mathrm{}\left(\mathrm{NiO}\right)\mathrm{}}_{0.75}$ ${\mathrm{}\left(\mathrm{FeO}\right)\mathrm{}}_{0.25}$ (${\mathrm{Fe}}_2$ ${\mathrm{O}}_3$). The resistivity $\rho$ of all samples over the same temperature range is also reported. At high temperatures, the extraordinary Hall coefficient $R_1$ for 99.9 Ni is proportional to ${\rho }^2$ as predicted by theory. However, the dependence upon $\rho$ 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 $R_1$, while $R_1$ in the high-concentration Ni samples is negative. $R_1$ for both ferrites is negative below about 400°C and positive above this temperature.