Rotational magnetization processes in exchange biased Ni81Fe19/Fe50Mn50 bilayers

The rotational magnetization process of an exchange coupled Ni81Fe19(10 nm)/Fe50Mn50(10 nm) bilayer was studied by Kerr microscopy. The domain processes in rotating magnetic fields near the exchange bias field H-eb are very sensitive to local variations of coupling strength and direction. A characteristic domain splitting was found that shows a remarkably different behavior for weaker and stronger coupled areas. While the magnetization in weaker coupled areas follows the rotating field for H approximate to H-eb, the stronger coupled areas switch back spring-like. As a result high-angle walls are formed between both areas causing rotational hysteresis. (C) 2002 Elsevier Science B.V. All rights reserved.