The effects of demagnetizing and stray fields on magnetoacoustic emission

Abstract

Magnetoacoustic emission (MAE) has been measured from a Ni bar and a mild steel bar. The magnetizing field was produced by a c-core electromagnet, which was separated from the specimen surface by a nonmagnetic spacer layer (thickness la). In Ni, the MAE profile contains a single peak when la is small. As la increases, a second peak appears and then a third peak, indicating that MAE is not only caused by domain wall creation and annihilation, but also by domain wall motion. In the case of the mild steel bar, only two peaks are detected, which are increasingly separated as la increases. The different results between the two materials can be explained by the different mobility of non-180° domain walls. The present results also indicate that the MAE profile obtained from Ni is less sensitive to la than that obtained from mild steel. This difference can be explained by considering the reluctance of the magnetic circuit.