Magnetoresistance of Iron Whiskers

Transverse magnetoresistance measurements on iron whiskers with axes along $〈100〉$, $〈110〉$, and $〈111〉$ have been made in fields up to 50 kOe. Measurements have been made on whiskers with diameters ranging from 40 to 400 μ. Sharp minima observed in the rotation diagrams measured at 50 kOe for all three orientations are consistent with the existence of open orbits along $〈100〉$ and $〈110〉$ directions. The field dependence curves show a region of negative magnetoresistance at low fields and at high fields the resistance varies as $B^m$, where $1<m<\mathrm{}2\mathrm{}$. The extent of the negative magnetoresistance region depends both on the field orientation and the diameter of the whisker and appears to be correlated with the domain structure. A size effect has also been observed on the field dependence of resistance at high fields and on the residual resistance ratio $\frac{{\rho }_{\mathrm{RT}}}{{{\rho }_{4.2}}^{\circ }}$. Values of $\frac{{\rho }_{\mathrm{RT}}}{{{\rho }_{4.2}}^{\circ }}$ range from 200 to 2000 for the whiskers which have been measured.