Analysis of Magnetization Reversal Process of Nd–Fe–B Sintered Magnets by Magnetic Domain Observation Using Kerr Microscope
We used a Kerr microscope, image processing, and photo editing to clarify magnetization reversal and its propagation in a sintered Nd-Fe-B magnet. Magnetic domain change was observed when a dc field from +20 to 20 kOe was applied to a sintered Nd-Fe-B magnet. Simultaneous magnetization reversal in several grains along the easy axis direction and its propagation to neighboring grains occurred. This indicates that the nucleation field in a grain and magnetic interaction between grains are important controlling factors of the coercivity of sintered Nd-Fe-B magnets.
Domain observation technique for Nd–Fe–B magnet in high magnetic field by image processing using liquid crystal modulator
A different domain observation technique by modulation of a polarizing plane has been developed for Nd–Fe–B sintered magnets. A liquid crystal element inserted in a longitudinal Kerr microscope is used as an optical modulator to acquire a reference image needed to enhance Kerr contrast by image processing. Domain images of the Nd–Fe–B magnet can be clearly observed by this technique in a high magnetic field up to 4.4kOe. It was found that polishing of the sintered magnet reduced its coercive force.
Enhancement of magneto-optical domain observation by digital image processing
An electronic system is described which allows to subtract contrast of non-magnetic origin from a magneto-optic image. At the same time image noise can be reduced to such a degree that the contrast visibility limit in domain observation is expanded by at least an order of magnitude. The system is demonstrated for a number of applications in which domain analysis was not possible before. These include magnetostriction-free metallic glasses, non-oriented silicon-iron steel and polycrystalline Ni-Fe samples. For the first time the internal wall structure could be made visible on metallic samples with magneto-optical means.