Correlation of dislocation and domain structure of Cr(001) investigated by spin-polarized scanning tunneling microscopy

The Cr(001) surface has been investigated by spin-polarized scanning tunneling microscopy to image various defects and their effect on the magnetic structure at the surface. The usual magnetic structure is determined by the antiferromagnetic ordering of Cr leading to the topological antiferromagnetism of the (001) surface. We found that screw dislocations result in the formation of domain walls with a width of 120-170 nm. The dependence of the domain-wall width on the distance from the screw dislocation is studied experimentally and compared to micromagnetic simulations. Our results show that the size and shape of the spin structure is determined by two parameters, the exchange stiffness and the effective anisotropy. Subsurface step dislocations lead to an s-like bending of step edges on the sample surface. In spite of the step bending the topological antiferromagnetic order is strictly maintained. In some rare cases large scale images show a change of the spin-polarized part of the tunneling current. It is explained by the fourfold symmetry of the Cr(001) surface which leads to a 90degrees degeneracy and the formation of according domains.