Dynamic Magneto-Optical Imaging of Domains in Grain-Oriented Electrical Steel

Abstract

Magneto-optical imaging with magneto-optical indicator films (MOIF) is a versatile method to characterize magnetic field distributions especially for material development and quality control. Magnetic domains and grains in grain-oriented electrical steel can be visualized, and quantified without removing the isolation layer. The combination of MOIF with digital high-speed camera technology enables temporally resolved investigations of the magnetization processes. In contrast to Kerr-effect measurements MOIF imaging works without sample preparation and even in the presence of industrial insulation coatings. Optical resolution of 25 microns and temporal resolution of 1 ms in single-shot mode could be demonstrated.

Volumetrically scanning the structure of stray-fields above grain-oriented electrical-steel using a variably angled TMR sensor

“…However, for the first time, the stray fields from surface domains viewed by other techniques [1,2,3] in only a planar (x,y) projection have been studied in the (x,z) plane perpendicular to the surface. The strength and extent of the fields have been quantified and progress made towards demonstrating their shape, and how it varies spatially in the surface boundary layer with the underlying domain structure.…”

“…The Kerr effect [2], and observational techniques derived from both such as MOIF [3], reveal the body of domains through their interaction with polarized light. It might be expected that magneto-resistive sensors in a scanning microscope, measuring stray fields, would also highlight the edges of domains where the stray fields are presumed strongest.…”

Visualization of Magnetic Domains in Electrical Steel Using High-Resolution Dark-Field Imaging

“…Furthermore, the dynamic domain imaging at power frequencies have been investigated [16,17]. However, since the above-mentioned techniques are surface-sensitive the results strongly depend on the thickness and the preparation state of the sample.…”

Dynamic volume magnetic domain wall imaging in grain oriented electrical steel at power frequencies with accumulative high-frame rate neutron dark-field imaging

“…Surface dynamic domain observation can be done by high-voltage scanning electron microscope 7 , 8 with insulating coating. Recent developments in imaging with magneto-optical indicator films (MOIF) make it possible to perform dynamic investigations at a frequency of 50 Hz while keeping the coating intact 9 . However, while MOIF enables the visual analysis of domain wall motion it is still limited to surface domain behavior.…”

“…utilizing on light or electrons, makes it possible to study bulk behavior of magnetic domain walls while keeping the insulating coating intact and thus without modifying the domain structure. The dark-field image (DFI) of neutron grating interferometry (nGI) 9 recently emerged as a valuable complementary technique to the established domain observation methods because it is the only technique available that enables the spatially resolved analysis of bulk magnetic domain walls 5 , 12 – 15 deep in the volume of materials and thus provides unique information. The contrast is based on the small-angle scattering of neutrons at domain walls and the consequent disruption of a predefined interference pattern.…”