Direct observation of magnetic Barkhausen noise around grain boundaries with high-spatial-resolution magnetic Barkhausen noise sensor

Magnetic Barkhausen noise (MBN) is a useful signal for non-destructively characterizing various properties of ferromagnetic materials. It is suggested that MBN is mainly generated at grain boundaries because there are more pinning sites around grain boundaries. However, direct experimental proof is difficult because of the lack of high-spatial-resolution MBN sensor. This study focuses on examining MBN around grain boundaries using a custom-made high-spatial-resolution MBN sensor. Firstly, the magnetic domains and grain structure of an electrical steel were obtained using a magneto-optical Kerr effect microscope. Then, MBN signals inside grains and around grain boundaries were measured using the high-spatial-resolution MBN sensor. The experimental results reveal that MBN signals are more evident around grain boundaries, 32.5%-435.7% larger than that in the grain interior. Based on the experimental measurement, two-dimensional MBN mapping of the area containing grain boundaries was carried out, enabling the identification of the location of grain boundaries in millimeter-scale grains.