title: Adatoms and clusters of 3d transition metals on graphene: electronic and magnetic configurations.
abstract: We investigate the electronic and magnetic properties of single Fe, Co, and Ni atoms and clusters on monolayer graphene (MLG) on SiC(0001) by means of scanning tunneling microscopy (STM), x-ray absorption spectroscopy, x-ray magnetic circular dichroism (XMCD), and ab initio calculations. STM reveals different adsorption sites for Ni and Co adatoms. XMCD proves Fe and Co adatoms to be paramagnetic and to exhibit an out-of-plane easy axis in agreement with theory. In contrast, we experimentally find a nonmagnetic ground state for Ni monomers while an increasing cluster size leads to sizeable magnetic moments. These observations are well reproduced by our calculations and reveal the importance of hybridization effects and intra-atomic charge transfer for the properties of adatoms and clusters on MLG.
authors.affiliation: Institute of Applied Physics, University of Hamburg, Jungiusstrasse 11, D-20355 Hamburg, Germany. teelbo@physnet.uni-hamburg.de
authors.forename: T
authors.initials: T
authors.lastname: Eelbo
authors.forename: M
authors.initials: M
authors.lastname: Waśniowska
authors.forename: P
authors.initials: P
authors.lastname: Thakur
authors.forename: M
authors.initials: M
authors.lastname: Gyamfi
authors.forename: B
authors.initials: B
authors.lastname: Sachs
authors.forename: T O
authors.initials: TO
authors.lastname: Wehling
authors.forename: S
authors.initials: S
authors.lastname: Forti
authors.forename: U
authors.initials: U
authors.lastname: Starke
authors.forename: C
authors.initials: C
authors.lastname: Tieg
authors.forename: A I
authors.initials: AI
authors.lastname: Lichtenstein
authors.forename: R
authors.initials: R
authors.lastname: Wiesendanger