Magnetic Domains by the Longitudinal Kerr Effect

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Abstract
Rotation of the polarization plane of obliquely incident light reflected from a polished ferromagnetic surface is successfully employed to reveal the antiparallel domains lying in the surface of a large single crystal of silicon iron. This Kerr magneto-optic effect is the basis of two methods of domain observation which are described in detail: (1) the optical probe method in which a small, focused beam of plane polarized light scans the crystal surface before being reflected into a photomultiplier tube located behind the Nicol prism analyzer, and (2) the photographic method in which the crystal surface is broadly illuminated with polarized light and the reflected beam is photographically recorded after passage through the analyzer. The truly saturated character of the domains is demonstrated, and the directions of the domains are assigned without ambiguity. Domain wall movement and Barkhausen discontinuities are revealed in photographs taken as the crystal is subjected to a changing magnetizing field. Possible applications and limitations of the method are discussed.