Multi-instrumental approach to domain walls and their movement in ferromagnetic steels – Origin of Barkhausen noise studied by microscopy techniques

• Published in: Materials & design 2023-10, Vol.234, p.112308, Article 112308
• Main Authors: Santa-aho, Suvi, Honkanen, Mari, Kaappa, Sami, Azzari, Lucio, Saren, Andrey, Ullakko, Kari, Laurson, Lasse, Vippola, Minnamari
• Format: Article
• Language: English
• Subjects: Barkhausen noise; Domain wall dynamics; Ferromagnetic steel; Lorentz microscopy; Magnetic domains; Magnetic force microscopy
• ISSN: 0264-1275; 1873-4197
• DOI: 10.1016/j.matdes.2023.112308

[Display omitted] •Hypotheses related to the origin of Barkhausen noise signal are visualized and verified by multi-instrumental microscopy techniques.•Thorough characterization of plain ferrite, containing several features theoretically affecting BN output, enabled resolving origin of varying BN signal levels.•Multi-instrumental characterization of complex ferrite-pearlite elaborated interaction of domain walls and pinning sites, i.e., origin of BN.•Bulk and thin samples have a similar domain structure, but different BN signals due to contribution of thin sample’s both surfaces.•In-plane domain wall movement under out-of-plane applied magnetic field is explained using anisotropy energetics. Two steels, ferrite and ferrite-pearlite were thoroughly characterized by a multi-instrumental microscopy techniques to get detailed information about their microstructure and magnetic structure. Microstructural features act as pinning sites for the motion of magnetic domain walls (DWs) leading to changes in the magnetization of the sample. This phenomenon is the basis for industrially relevant non-destructive Barkhausen noise (BN) technique. With magnetic force microscopy (MFM), using bulk samples, and Lorentz microscopy, using thin films, we noticed that bulk and thin samples have similar domain structure still giving different BN signal amplitudes. We could explain an in-plane DW movement under out-of-plane applied magnetic field using anisotropy energetics. In-situ transmission electron microscopy (TEM) in Lorentz mode was used to visualize the motion of DWs and their interactions with different pinning sites. To help the interpretation of DW motions, alignment and denoising processes were tailored for in-situ TEM studies. Multi-instrumental and multidimensional structural analysis enabled us to visualize and verify many theoretical hypotheses related to the origin of BN signal in ferrite and ferrite-pearlite steels.