Formation of antiferromagnetic NiO spiral domain and its effect on the magnetic anisotropy in Py/NiO/Co_0.5 Ni_0.5O/vicinal Ag(001)

It has been a fundamental issue on how the Mauri’s model describes the effect of an antiferromagnetic (AFM) layer on a ferromagnetic (FM) layer. Although recent result shows that Mauri’s model not necessarily gives raise an exchange bias, it is unclear on how the planar spiral domain in the AFM layer induces a magnetic anisotropy in the FM layer in a FM/AFM system. Here we report an experimental study of Py/NiO/Co_0.5Ni_0.5O/vicinal Ag(001) system using x-ray linear dichroism (XMLD) and rotating magnetic field magneto-optic Kerr effect (ROTMOKE). The Co_0.5Ni_0.5O layer has frozen AFM spins which are aligned by atomic steps of the vicinal surface so that they pin the NiO spin orientation at the NiO/Co_0.5Ni_0.5O interface. In this way, as the top Py layer magnetization is rotated by an external magnetic field, the Py/NiO interfacial coupling rotates the NiO spins at the FM/NiO interface to twist the NiO spins into a planar spiral domain. We find that the NiO AFM spins are almost frozen below ~3nm thickness, gradually develop a planar spiral domain wall in the range of 3-16nm, and complete the domain wall formation thicker than ~16nm. Correspondingly, the frozen, incomplete spiral, and complete spiral NiO domain walls are well revealed in the magnetic anisotropy of the Py layer.