Frequency dependence of the magnetostrictive phenomenon in Metglas® 2605SA1 ribbon: A minor-loop case

Frequency dependence of magnetostrictive phenomenon of as-cast 2605SA1 ribbon was studied. We applied a sinusoidal sweeping field (H), with a fixed frequency (f), along length (L) of the ribbon, and simultaneously recorded the longitudinal magnetostriction (λ∥) and the transverse magnetostriction (λ⊥) as a function of time (t), respectively. f was varied from 0.07 to 122 Hz. In the low-f case (f =0.07 Hz), we observed the frequency-doubling (FD) feature in λ∥(t) and λ⊥(t) curves; i.e., only even harmonic magnetostrictive signals showed up. In the high-f case (f = 122 Hz), we observed the no-frequency-doubling (NFD) feature; i.e., both odd and even harmonic magnetostrictive signals showed up. A theory, based on the balance among various torques acting on magnetization, is developed to explain the f dependence of the magnetostriction phenomenon observed. From this theory, we conclude that only when the reflection symmetry of the system is reserved, i.e., when the equivalent easy axis (EEA) is perpendicular to L, will λ∥(t) and λ⊥(t) have the true-frequency-doubling (TFD) feature. However, for the as-cast 2605SA1 ribbon, EEA is not perpendicular to L. Thus, strictly speaking, we should observe the NFD feature only. Nevertheless, in the low-f limit, we can show that the FD feature is somewhat allowed under the condition, b/α being close to 1, where b and α are the two parameters used in the theory. From experimental data, this condition is met for as-cast 2605SA1. To make a distinction from TFD, this low-f feature is called close-frequency-doubling (CFD) in this paper. In general, the theory explains all the experimental results fairly well.