Multi-scale magnetic study on Ni(111) and graphene on Ni(111)

摘要

We have investigated the magnetism of the bare and graphene-covered (111)surface of a Ni single crystal employing three different magnetic imagingtechniques and ab initio calculations, covering length scales from thenanometer regime up to several millimeters. With low temperature spinpolarizedscanning tunneling microscopy (SP-STM) we find domain walls with widths of 60 -90 nm, which can be moved by small perpendicular magnetic fields. Spin contrastis also achieved on the graphene-covered surface, which means that the electrondensity in the vacuum above graphene is substantially spin-polarized. Inaccordance with our ab initio calculations we find an enhanced atomiccorrugation with respect to the bare surface, due to the presence of the carbonpz orbitals and as a result of the quenching of Ni surface states. The latteralso leads to an inversion of spinpolarization with respect to the pristinesurface. Room temperature Kerr microscopy shows a stripe like domain patternwith stripe widths of 3 - 6 {\mu}m. Applying in-plane-fields, domain wallsstart to move at about 13 mT and a single domain state is achieved at 140 mT.Via scanning electron microscopy with polarization analysis (SEMPA) a secondtype of modulation within the stripes is found and identified as 330 nm wideV-lines. Qualitatively, the observed surface domain pattern originates frombulk domains and their quasi-domain branching is driven by stray fieldreduction.