Critical angle for irreversible switching of the exchange-bias direction in NiO-Cu-Ni81Fe19 films -: art. no. 054405

The stability of the reference magnetization in exchange-biased NiO (10-13 nm)/Cu (0.2-0.8 nm)/Permalloy (10 nm) layers was investigated by Kerr microscopic domain studies in an optical cryostat. The stability of the coupling was found to depend on temperature and on the direction of an applied magnetic field. We discovered different blocking temperatures T-B,T-hard>T-B,T-easy for hard and easy axis magnetization reversals. Moving 180degrees domain walls are able to permanently switch the pinning direction by 180degrees. In rotational field experiments it could be proved that it is not the wall itself that acts on the antiferromagnet, but rather the torque of the ferromagnetic moment at the interface that probably remagnetizes the antiferromagnetic film by motion of a Bloch wall parallel to the film plane. We determined a critical angle alpha(C) for permanent switching which depends on temperature.