Hot Electrons in Germanium and Ohm's Law

The elastic constants of nickel crystals, and their variation with magnetic field (ΔE effect), have been measured by a 10-megacycle ultrasonic pulsing method. The constants of three crystals agree well with one another when the crystals are magnetically saturated, but vary with domain distribution when demagnetized. The maximum ΔE effect observed is much less (3%) than has been observed at lower frequencies (20%). By measuring the ΔE effect and the decrement of polycrystalline rods at low frequencies, it is shown that the small effect observed at 10 megacycles is due to a relaxation in the domain wall motion due to microeddy-current damping. From the initial slope of the decrement-frequency curve, and also from the frequency of maximum decrement, the size of the average domain is found to he about 0.04 mm. Actual domains in single nickel crystals have been observed optically by Williams, who finds domain widths of 0.02 to 0.2 mm.