MAGNETOOPTICAL KERR EFFECT ON MAGNETIC CRYSTALS WITH EXTERNALLY APPLIED MAGNETIC-FIELDS

Magnetic domain structures of a multidomain magnetite crystal were observed as a function of applied magnetic field with the magneto-optical Kerr effect. Normal and reverse magnetic fields were applied from zero to 165 mT until the grain was nearly saturated. The magnetic hysteresis, determined from the domain patterns on the surface of a single crystal, was inconsistent with bulk hysteresis measurements on magnetite of equivalent grain size. A nearly single-domain configuration at zero field for the remanence state was interpreted as a surface phenomenon concealing magnetic domains in the interior of the grain. A model is presented in which magnetization lies in the observed plane and domain walls are dipping at a shallow angle.