Evaluation of surface-modified materials by model assisted analyses of Barkhausen effect signals

Barkhausen effect (BE) measurements offer a useful technique for evaluation of surface conditions of magnetic materials. Theoretical analysis of BE signals has nevertheless remained a challenge due to a lack of adequate model description of the phenomenon. This paper presents model‐assisted analysis of BE signals with an aim of evaluating surface‐modified materials whose magnetic properties vary continuously with depth. The approach is based on an extended BE model which describes the signal power spectrum. In the extended model, the local fluctuation of pinning field and correlation length parameters, which characterize domain wall motion and hence the generation of BE signals, are related to the domain wall pinning strength which vary with depth as described in terms of a parametrized function. In this study, the BE signals measured over a broad frequency range from carburized steels and oxidized Ni97Al3 were analyzed using multiple frequency passbands to extract signals generated at different depths. Depth profiles of the pinning field fluctuation and correlation length were determined by obtaining the best fit of the modeled BE signal power to the experimental data. The inverted profiles show changes at depths which agree with case depths of the carburized steel samples, and with the oxidization depths of the Ni97Al3 samples