Barkhausen noise measurements give direct observation of magnetocrystalline anisotropy energy in ferromagnetic polycrystals

This paper presents experimental evidence of the capability of Barkhausen noise measurements to estimate the angular dependence of the average magnetocrystalline energy in soft magnetic polycrystalline materials. Three different API 5L steel samples, all obtained from out-of-service pipelines, were investigated using crystallographic texture and Barkhausen noise measurements. The angular dependence of the rms voltage of the Barkhausen signal was determined in each sample for the time band corresponding to the saturation-to-remanence part of the hysteresis loop where irreversible domain rotation occurs. For each angular position, the rms voltage of the Barkhausen noise signal in this time band was interpreted as a direct measure of the magnetocrystalline anisotropy energy of the polycrystal in the corresponding direction. A strong correlation between the angular dependence of both the rms voltage of the Barkhausen signal in the time band of interest and the average magnetocrystalline energy obtained from crystallographic texture measurements was found experimentally.