Hall effect in iron from 1 to 250 K and to 150 kOe

The Hall effect in 〈111〉 iron whiskers with residual resistivity ratios of 3166 and 4000 has been measured in the temperature range 1-247 K. Data for all temperatures in this range have been taken in the field range 15-45 kOe while data at 63.5 and 4.2 K up to 150 kOe have been analyzed. Above 100 K the ordinary Hall coefficient $R_0$ is linear in both temperature and magnetic field while the ferromagnetic Hall coefficient $R_s$ is nearly proportional to ${\rho }^2$ with $R_s = \left(\frac{1.44\times {10}^3}{4\pi M_s}\right){\rho }^{1.94}$. At temperatures below 80 K the Hall resistivity decreases rapidly with temperature and changes sign from positive to negative at ∼70 K. It also develops a strong field-dependent curvature below 80 K. This has been taken into account by analyzing Kohler plots of the data over the entire range of temperature and magnetic field. Results suggest that transitions of the carriers from the low-field to the high-field limit may play a critical role in the low-temperature range. Deviations from the Kohler plot are observed between 40 and 20 K and these correspond to an anomalous plateau in the temperature dependence of the Hall resistivity. At 4.2 K the Hall resistivity shows a strong field-dependent curvature up to 100 kOe but is linear in the range 100-150 kOe. Extrapolation of the linear portion to $B=0\mathrm{}$ gives a zero intercept indicating that $R_s$ vanishes at helium temperatures. The curvature may result from a mobility transition, but open orbits or magnetic breakdown can also be playing a role. Full discussion of these points is included.