Magnetoresistance and Domain Theory of Iron-Nickel Alloys

Measurements of change of electrical resistivity with magnetization and with tension are reported for iron-nickel alloys containing 40 to 100 percent nickel. When the magnetostriction is negative (81 to 100 percent nickel), tension ($\sigma$) decreases resistivity, and magnetic field ($H$) increases it. Domain theory predicts the ratio $\frac{\sigma }{H}$ at which the resistivity is equal to that of the unmagnetized specimen, and the theory is accurately confirmed. Measurements are made in transverse as well as longitudinal magnetic fields, and the difference between the resistances so measured is shown to be independent of the distribution of domains in the unmagnetized state; the erratic results reported in the literature are thus explained and avoided. When magnetostriction is positive, the limiting changes of resistivity with field and tension are sometimes found to be different; this is shown to be caused by the variation of magnetostriction with crystallographic direction.