Temperature Dependence of Magnetoresistance in Iron

Longitudinal and transverse magnetoresistance has been measured in iron single crystals at 300, 77, and 4.2°K in fields up to 50 kOe. For most field and current directions the magnetoresistance reverses sign between 300 and 4.2°K in both high and low fields. At 300°K the magnetoresistance shows an initial positive region connected with the magnetization process, while at high fields it shifts to a negative slope. At low temperatures the low-field magnetoresistance becomes negative and at 4.2°K the longitudinal and transverse magnetoresistance reach minimum values at 400-1000 Oe and 1-6 kOe, respectively. Both the transverse and longitudinal magnetoresistance show hysteresis within the negative region, and the decrease in resistance depends on the development of a net magnetization in the direction of the applied field. The negative magnetoresistance does not seem to be a sensitive function of domain configuration. The high-field magnetoresistance at 4.2°K is typical of a compensated metal and corresponds to ${\omega }_c\tau >1\mathrm{}$, where ${\omega }_c$ is the cyclotron frequency and $\tau$ the relaxation time. Iron whiskers 180-400 μ in diameter with axes along $〈100〉$ and $〈111〉$ directions have been used for the experiments and have resistance ratios $\frac{{{{\rho }_{300}}^{\circ }}_{\mathrm{K}}}{{{{\rho }_{4.2}}^{\circ }}_{\mathrm{K}}}$ that vary from 200 to 2000.