The dependence of magnetoacoustic emission on magnetizing frequency in nickel and mild steel

Magnetoacoustic emission (MAE) measurements have been made on nickel and mild steel samples subjected to a magnetizing field of various frequencies f. In both samples, the MAE signals are found to increase with increasing f. The experimental results are in good agreement with the predictions of a model relating the generation of MAE to domain wall nucleation-annihilation and domain wall motion. When f is large, the contribution of wall motion to the generation of MAE is predicted to be dominant. Conversely, when f is small, MAE is generated mainly by domain wall nucleation-annihilation processes. At high frequencies, the amount of MAE from both nickel and mild steel samples is found to vary linearly with f(0.5). As f decreases, the MAE deviates from the f(0.5) relationship for f < 10 Hz in mild steel, and for f < 2 Hz for nickel. The results suggest that in nickel, wall motion remains the dominant source of MAE generation over a wider frequency range than in steel. (C) 1996 American Institute of Physics.