title: Reaching the magnetic anisotropy limit of a 3d metal atom.
abstract: Designing systems with large magnetic anisotropy is critical to realize nanoscopic magnets. Thus far, the magnetic anisotropy energy per atom in single-molecule magnets and ferromagnetic films remains typically one to two orders of magnitude below the theoretical limit imposed by the atomic spin-orbit interaction. We realized the maximum magnetic anisotropy for a 3d transition metal atom by coordinating a single Co atom to the O site of an MgO(100) surface. Scanning tunneling spectroscopy reveals a record-high zero-field splitting of 58 millielectron volts as well as slow relaxation of the Co atom's magnetization. This striking behavior originates from the dominating axial ligand field at the O adsorption site, which leads to out-of-plane uniaxial anisotropy while preserving the gas-phase orbital moment of Co, as observed with x-ray magnetic circular dichroism.
authors.affiliation: IBM Almaden Research Center, 650 Harry Road, San Jose, CA 95120, USA.
authors.forename: Ileana G
authors.initials: IG
authors.lastname: Rau
authors.affiliation: IBM Almaden Research Center, 650 Harry Road, San Jose, CA 95120, USA. Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland.
authors.forename: Susanne
authors.initials: S
authors.lastname: Baumann
authors.affiliation: Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland.
authors.forename: Stefano
authors.initials: S
authors.lastname: Rusponi
authors.affiliation: Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland.
authors.forename: Fabio
authors.initials: F
authors.lastname: Donati
authors.affiliation: Department of Materials, Eidgenössische Technische Hochschule (ETH) Zürich, Hönggerbergring 64, CH-8093 Zürich, Switzerland.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Stepanow
authors.affiliation: Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland.
authors.forename: Luca
authors.initials: L
authors.lastname: Gragnaniello
authors.affiliation: Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland. Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland.
authors.forename: Jan
authors.initials: J
authors.lastname: Dreiser
authors.affiliation: Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland.
authors.forename: Cinthia
authors.initials: C
authors.lastname: Piamonteze
authors.affiliation: Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland.
authors.forename: Frithjof
authors.initials: F
authors.lastname: Nolting
authors.affiliation: IBM Almaden Research Center, 650 Harry Road, San Jose, CA 95120, USA.
authors.forename: Shruba
authors.initials: S
authors.lastname: Gangopadhyay
authors.affiliation: IBM Almaden Research Center, 650 Harry Road, San Jose, CA 95120, USA. Department of Physics, Georgetown University, 3700 O Street NW, Washington, DC 20057, USA.
authors.forename: Oliver R
authors.initials: OR
authors.lastname: Albertini
authors.affiliation: IBM Almaden Research Center, 650 Harry Road, San Jose, CA 95120, USA.
authors.forename: Roger M
authors.initials: RM
authors.lastname: Macfarlane
authors.affiliation: IBM Almaden Research Center, 650 Harry Road, San Jose, CA 95120, USA.
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Lutz
authors.affiliation: IBM Almaden Research Center, 650 Harry Road, San Jose, CA 95120, USA.
authors.forename: Barbara A
authors.initials: BA
authors.lastname: Jones
authors.affiliation: Department of Materials, Eidgenössische Technische Hochschule (ETH) Zürich, Hönggerbergring 64, CH-8093 Zürich, Switzerland. andreash@us.ibm.com pietro.gambardella@mat.ethz.ch harald.brune@epfl.ch.
authors.forename: Pietro
authors.initials: P
authors.lastname: Gambardella
authors.affiliation: IBM Almaden Research Center, 650 Harry Road, San Jose, CA 95120, USA. andreash@us.ibm.com pietro.gambardella@mat.ethz.ch harald.brune@epfl.ch.
authors.forename: Andreas J
authors.initials: AJ
authors.lastname: Heinrich
authors.affiliation: Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland. andreash@us.ibm.com pietro.gambardella@mat.ethz.ch harald.brune@epfl.ch.
authors.forename: Harald
authors.initials: H
authors.lastname: Brune