The longitudinal magneto-resistance effect in single crystals of iron

Abstract

The change of resistance of iron when placed in a magnetic field parallel to the direction of the current has frequently been investigated since its discovery by Sir William Thomson in 1856. The many measurements are in general agreement, and show that the resistance of ordinary iron is always increased by a longitudinal magnetic field. The amount of the change of resistance increases with the strength of the magnetic field until magnetic saturation is approached, when it tends to a limiting value of about 0·20 percent. The phenomenon till now has been measured only in ordinary soft iron consisting of an indeterminate mass of small crystals, so that there was no information as to the effect of crystal structure on the change of resistance. However, the fact that many ferro-magnetic phenomena were very sensitive to changes in the physical state of the specimen in which they were examined has suggested that these phenomena would be different in different directions in a single crystal. The writer has already shown that in the case of magnetostriction the direction in the crystal in which the effect is measured is of paramount importance in determining not only the magnitude but also the sign of the change of length. It seemed, therefore, to be important to determine whether there was any corresponding effect of crystal structure on the change of resistance produced by a longitudinal magnetic field.