Magnetization process in electrical steel sheets
Electrical Energy Systems, Power Management, Power Electronics, Electrical Machines and Drives
Experimental Condensed Matter Physics
Final Report Abstract
This project was dedicated to the investigation of the quasi-static and dynamic magnetic reversal processes in polycrystalline, soft magnetic bulk materials with electrical steel as a typical representative by means of wide-field magneto-optical Kerr microscopy, applied directly or indirectly (by using magneto-optical indicator film with perpendicular anisotropy (PMOIF)). During the project period, a software package was developed that allows to calculate the magnetic hardness of the grain boundaries of an FeSi steel sample with cubic magnetocrystalline anisotropy, with an experimentally obtained EBSD plot as input and based on a quasi-domain model. The goal was the experimental verification of the quasi-domain model and its suitability to describe the flux propagation across grain boundaries. Our studies have shown that the proposed model can indeed be used to estimate the magnetic grain boundary hardness. However further analysis is needed to account for the size and shape of the grains, and the direction of the external magnetic field applied during the measurement. It was furthermore shown that the PMOIF technique can be utilized for the investigation of static and dynamic magnetization processes in grain-oriented electrical steel under application-relevant conditions. The potential of PMOIF imaging in comparison with well established Kerr microscopy was examined. Differences between quasistatic and dynamic processes were elaborated, revealing the mechanisms of domain refinement and showing the role of grain boundaries and mechanical stress on domain formation and flux propagation. It was found that magnetic pole contrast at grain boundaries appears at magnetically soft grain boundaries, while hard boundaries are characterized by stiffened spike domains. It is expected that any grain boundary shows both properties at opposite surfaces. In addition to addressing the fundamental questions within the project, activities were also dedicated to the improvement of wide-field Kerr microscopy. It turned out that the direction of sensitivity strongly depends on the mutual orientation of the light polarization plane, the plane of incidence and the opening angle of the analyzer. An advanced software for magnetic anisotropy studies has been developed. Furthermore, the applicability of other magneto-optical effects besides the Kerr effect was systematically investigated. Both papers were triggered by studies that were initiated by this project. Our investigations furthermore show that MOKE magnetometry has to be treated with care. By measuring and comparing the local hysteresis loops with the global loops we have identified inverted loops which require analysis on the basis of the Preisach model. Just taking a local MOKE loop in an extend sample, which is the common case, is meaningless.
Publications
- Power frequency domain imaging on Goss-textured electrical steel. JMMM 474, 221 (2018)
Rudolf Schäfer, Ivan Soldatov, Satoshi Arai
(See online at https://doi.org/10.1016/j.jmmm.2018.10.100) - Inverted Hysteresis, Magnetic Domains, and Hysterons. IEEE Magnetics Letters, vol. 11, pp. 1-5, (2020)
Ivan Soldatov, Petru Andrei, Rudolf Schäfer
(See online at https://doi.org/10.1109/LMAG.2020.3035136) - Advanced, Kerr-microscopy-based MOKE magnetometry for the anisotropy characterisation of magnetic films. JMMM 529, 167889 (2021)
IV Soldatov, J Zehner, K Leistner, T Kang, D Karnaushenko, R Schäfer
(See online at https://doi.org/10.1016/j.jmmm.2021.167889) - Analyzer-free, intensity-based, wide-field magneto-optical microscopy. Applied Physics Reviews 8, 031402 (2021)
Rudolf Schäfer, Peter M. Oppeneer, Alexey V. Ognev, Alexander S. Samardak and Ivan V. Soldatov
(See online at https://doi.org/10.1063/5.0051599) - Interpretation of Kerr Microscopic Domain Contrast on Curved Surfaces. IEEE Magnetics Letters, vol. 12, pp. 1-4, (2021)
Ivan Soldatov, Valeria Kolesnikova, Valeria Rodionova, Rudolf Schäfer
(See online at https://doi.org/10.1109/LMAG.2021.3116791) - Role of the interfaces in the crystallization and hysteresis mechanisms of amorphous Fe-B thin films. Journal of Alloys and Compounds 869, 159276 (2021)
Unai Urdiroz, F Javier Palomares, A Mayoral, IV Soldatov, R Schäfer, JM Gonzalez, Marta Sanchez-Agudo, E Navarro, A Ruiz, María Alonso, Luis Vázquez, F Cebollada
(See online at https://doi.org/10.1016/j.jallcom.2021.159276)
