Resistivity of Iron as a Function of Magnetization and Stress

The resistance and magnetoresistance of iron single crystals have been measured as a function of stress at liquid-helium temperatures. For measuring currents above some critical value, a large transition in the resistance of the sample is observed, and the critical current for this transition is a function of both the applied longitudinal magnetic field and the applied axial stress. The results have been interpreted in terms of inverse-magnetostriction and domain-reorientation effects involving the self-field of the current. We have developed a model for the $〈100〉$-axial crystals based on a sheath-core configuration with spins perpendicular and parallel to the current in the sheath and core, respectively. Under favorable conditions the formation of the sheath-core configuration simulates the behavior of thermodynamical variables in a first-order phase transition. The analysis of the model can be used to predict the observed resistance transition quite accurately and can also be used to obtain a value of the saturation magnetostriction constant ${\lambda }_{100}$. The value obtained is ${\lambda }_{100}=(25.0\mathrm{}\pm 1.0)\times {10}^{-6\mathrm{}}$, which is in reasonable agreement with other measurements. Results of stress experiments on $〈111〉$-axial crystals are consistent with a negative value of ${\lambda }_{111}$, but indicate that the field and current-induced resistance transitions are more complex than those in the $〈100〉$-axial crystals. Discussion of possible mechanisms is included.