Sputtered exchange-coupled sandwich systems with FeMn biasing underlayer, NiFe and NiCo ferromagnetic layers, and wedge-shaped Ru interlayers are investigated by Kerr microscopy. Domain analysis confirms the basic oscillatory behavior between ferro- and antiferromagnetic exchange coupling as a function of the nonmagnetic interlayer thickness. High resolution observation reveals many 360 degrees domain walls, especially in zones of weak coupling. These 360 degrees walls act as nucleation sites in a strongly hysteretic magnetization process and may form a problem in sensor applications.
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