Galvanomagnetic Effects in Iron Whiskers

Abstract

Measurements have been made of the temperature dependence of the Hall effect in the range 1-300\ifmmode^\circ\else\textdegree\fi{}K, and of the transverse and longitudinal magnetoresistance at low temperatures, in [100] and [111] iron whiskers of high purity (resistance ratios extrapolated to $B=0$ 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 ${R}_{s}\ensuremath{\propto}{\ensuremath{\rho}}^{2}$, where $\ensuremath{\rho}$ 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\ifmmode^\circ\else\textdegree\fi{}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 (\ensuremath{\sim}10%) has also been observed for some specimens in weak transverse fields.