Barkhausen noise in cold rolled 78.5％ permalloy and deformed mild steel

Abstract

The Barkhausen noise, its frequency spectrum and the hysteresis loops of coldrolled 78\% permalloy have been studied during magnetization cycle at different magnetizing frequencies. The hysteresis loss did not change at different magnetizing frequencies (0.05 Hz, 10 Hz and 90 Hz), but the average amplitude of Barkhausen noise was larger at higher magnetizing frequency (in the range of 0.01 - 1Hz), that is, Barkhausen noise have the tendency to be clustered more strongly at higher magnetizing frequency. The magnitude of the frequency spectrum was greatest near Hc, that is, the clustering mature of Barkhausen noise is predominant at the steepest parts of the hysteresis loop. The hysteresis loop and Barkhausen noise of deformed mild steel were measured. When the deformation became more severe, the magnetic property was harder. This is supposed to be due to the increase of dislocation densities which act as barriers to the domain wall motion, and this was confirmed by the measurement of Barkhausen noise, average amplitude of which increased when the deformation became more and more severe.