Magnetoresistance in Iron Single Crystals

Magnetoresistance in single crystals of iron has been studied in fields up to 50 kOe at temperatures from 1°-300°K. Iron whiskers 40-700 μ in diameter grown by the hydrogen reduction fo FeCl₂ and having residual resistance ratios ρ_300°K/p_4.2°K from 200 to 2000 have been used for the experiments. In low fields the magnetoresistance shows a behavior related to the development of a net magnetization through domain growth and spin rotation. At low temperatures the predominant low-field behavior consists of a large negative magnetoresistance which develops for both transverse and longitudinal field orientations. This effect is present at 77°K and increases by an order of magnitude at 4.2°K. Strong hysteresis effects are also observed at 4.2°K. Correlation of the low-field magnetoresistance with the domain structure is discussed for both <100> and <111> axial whiskers. At high fields and low temperatures the magnetoresistance is in general agreement with theory and indicates that open orbits may exist for certain field directions. At high temperatures the high-field behavior shows a negative slope in agreement with previous experiment and theory while at low fields structure associated with domain development is observed.