Magnetic-domain imaging techniques

Abstract

The concept of domains in ferromagnets was introduced by Weiss in 1906. However, they were not observed until 1931 when Bitter showed that domain boundaries could be observed by decorating them with fine magnetic particles. Since then the field of magnetic domain imaging has expanded enormously.The original Bitter technique involved the decoration of a magnetic sample with a colloidal suspension of fine magnetic particles (usually magnetite) and observation by dark field optical microscopy. This is still a commonly used method and has been extended to finer particles, which include clusters directly deposited on the magnetic sample from a chemical vapor and observation of the clusters in the SEM or TEM at magnifications in excess of 20,000x.Another very popular means of observing magnetic domains employs the magneto-optic Kerr effect. Both polar and longitudinal Kerr techniques has been utilized. In the polar Kerr technique a magnetic sample is illuminated by a beam of plane polarized light normal to the sample surface.