Defects in ferrite can change the local magnetic coupling from ferromagnetic to strongly antiferromagnetic. In eptiaxial magnetite ͑Fe 3 O 4 ͒ films, defects locally altering exchange interaction, i.e., "antiphase boundaries" ͑APB͒, essentially determine magnetic and magnetotransport properties. We locally observed specific magnetization reversal events in epitaxial magnetite Fe 3−␦ O 4 / MgO films ͑␦ Ϸ 0.03͒ by magnetic force microscopy in external magnetic fields. A dominating phenomenon is

more »

... nning of bubble domains at single APB. Pinning is a particular consequence of antiferromagnetic coupling across APB. Antiferromagnetic coupling across APB could be directly verified for a sample with an APB domain size above the resolution limit of magnetic force microscopy.