Chirality Switching and Winding or Unwinding of the Antiferromagnetic NiO Domain Walls in Fe / NiO / Fe / CoO / Ag ( 001 )

Fe/NiO/Fe/CoO/Ag(001) single crystalline films were grown epitaxially and investigated by x-ray magnetic circular dichroism and x-ray magnetic linear dichroism. The bottom Fe layer magnetization is pinned through exchange coupling to the CoO layer and the top Fe layer magnetization can be rotated by an in-plane external magnetic field. We find that the NiO spins wind up to form a domain wall due to the perpendicular NiO/Fe interfacial coupling as the top layer Fe magnetization rotates from 0 degrees to 90 degrees, but switch wall chirality and unwind the wall as the Fe magnetization rotates from 90 degrees to 180 degrees. This observation shows that Mauri's 180 degrees domain wall does not exist in perpendicularly coupled ferromagnetic-antiferromagnetic systems in the strong coupling regime.