Characterization of Magnetoacoustic Emission Related to Structural Properties of Ferromagnets

摘要

A series of magnetoacoustic emission (MAE) experiments was performed using sets of pure iron and low carbon steel samples with three different thicknesses. The appearance of the leading sub-peak of the MAE in the initial stage of reducing the magnetic induction from the saturated state was proved to be universal. Such an early appearance was explained in terms of the nucleation of the seed domains of reverse magnetization and follow-on expansion of these domains before the reversal of the applied magnetic field. The low MAE activity in the region of high pickup coil output was also shown to be a universal characteristic which was explained based on the dynamics of the 180 degrees domain wall that divides the specimen into two domains. The low mobility of 90 degrees domain walls, which are responsible for the generation of MAE, and the delayed motion of the 180 degrees domain wall due to eddy currents can explain the extended range of the MAE activity after the leading peak. The appearance of the three-peak structure in the two thinner samples, however, remains unexplained.