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 f0.5. As f decreases, the MAE deviates from the f0.5 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.