ΔE-effect and macroeddy-current damping in nickel

Internal friction measurements on nickel reeds have confirmed the macroeddy-current limited relaxation behavior predicted by Zener. The macroeddy-current peak has been observed as a function of frequency, and shown to depend in height and position on the magnetization of the sample. At low frequencies the modulus defect associated with this relaxation causes the ΔE-effect to exhibit a maximum value at an intermediate magnetization in the vicinity of half the saturation value. As the frequency is raised the maximum disappears and the behavior of the ΔE-effect reverts to that observed in resonant-rod experiments. It is emphasized that in this regime, which has frequently been used in the past, the measured ΔE-effect does not provide an equilibrium characterization of the material.