Galvanomagnetic Effects in Iron Whiskers

Measurements have been made of the temperature dependence of the Hall effect in the range 1-300°K, and of the transverse and longitudinal magnetoresistance at low temperatures, in [100] and [111] iron whiskers of high purity (resistance ratios extrapolated to $B=0\mathrm{}$ ranged from 242 to 852). Analysis of the Hall data shows that both the "ordinary" Hall coefficient $R_0$ and the "extraordinary" Hall coefficient $R_s$ vary enormously with temperature, and these variations cannot be explained by existing theories. The theoretical relation $R_s\propto {\rho }^2$, where $\rho$ is the resistivity, does not hold for temperatures below that of liquid nitrogen, and around this temperature $R_0$, which is positive at room temperature (hole conduction), becomes negative. $R_0$ and $R_s$ appear to be isotropic, but at low temperatures these coefficients are extremely sensitive to impurities. The longitudinal magnetoresistance at 4.2°K shows a large effect of the domain structure on the electrical resistance, which decreases appreciably (46% for the purest specimen) on magnetizing the specimens to saturation. Small negative magnetoresistance (∼10%) has also been observed for some specimens in weak transverse fields.