Antiferromagnetic domain structure imaging of cleaved NiO(100) surface using nonmagnetic linear dichroism at O K edge: Essential effect of antiferromagnetic crystal distortion

Antiferromagnetic (AFM) domain structures of a NiO(100) surface have been observed using a combined method of photoelectron emission microscopy (PEEM) and soft-X-ray linear dichroism (LD) at an O K edge. Since oxygen atoms in NiO crystal should not have any magnetic moment, this imaging result was unexpected. By evaporating the magnetic materials (Fe) on the NiO crystal, the observed domain structure of NiO at a Ni L edge was strongly affected by the exchange coupling between the magnetic thin film and the AFM substrate, whereas that at the O K edge was not. It is concluded from these results that the LD at the O K edge originates from the anisotropy due to the strong coupling with the Ni 3d orbital. The observed image at the O K edge reflects essentially the T-domain information concerning the AFM crystal distortion. In contrast, the domain structure observed at the Ni L edge seems to show both T- and S-domain patterns.