Europium Cyclooctatetraene Nanowire Carpets: A Low-Dimensional, Organometallic, and Ferromagnetic Insulator

Felix Huttmann; Nico Rothenbach; Stefan Kraus; Katharina Ollefs; Lucas M Arruda; Matthias Bernien; Danny Thonig; Anna Delin; Jonas Fransson; Kurt Kummer; Nicholas B Brookes; Olle Eriksson; Wolfgang Kuch; Thomas Michely; Heiko Wende

doi:10.1021/acs.jpclett.8b03711

Europium Cyclooctatetraene Nanowire Carpets: A Low-Dimensional, Organometallic, and Ferromagnetic Insulator

J Phys Chem Lett. 2019 Mar 7;10(5):911-917. doi: 10.1021/acs.jpclett.8b03711. Epub 2019 Feb 14.

Authors

Felix Huttmann¹, Nico Rothenbach², Stefan Kraus¹, Katharina Ollefs², Lucas M Arruda³, Matthias Bernien³, Danny Thonig⁴, Anna Delin^{4

5

6}, Jonas Fransson⁴, Kurt Kummer⁷, Nicholas B Brookes⁷, Olle Eriksson^{4

8}, Wolfgang Kuch³, Thomas Michely¹, Heiko Wende²

Affiliations

¹ II. Physikalisches Institut , Universität zu Köln , Zülpicher Strasse 77 , D-50937 Köln , Germany.
² Fakultät für Physik , Universität Duisburg-Essen and Center for Nanointegration Duisburg-Essen (CENIDE) , Lotharstr. 1 , D-47057 Duisburg , Germany.
³ Institut für Experimentalphysik , Freie Universität Berlin , Arnimallee 14 , 14195 Berlin , Germany.
⁴ Department of Physics and Astronomy, Materials Theory , Uppsala University , SE-75120 Uppsala , Sweden.
⁵ Department of Applied Physics, School of Engineering Sciences , KTH Royal Institute of Technology , Electrum 229 , SE-16440 Kista , Sweden.
⁶ SeRC (Swedish e-Science Research Center), KTH Royal Institute of Technology , SE-10044 Stockholm , Sweden.
⁷ European Synchrotron Radiation Facility , 71 Avenue des Martyrs, CS40220 , F-38043 Grenoble , Cedex 9, France.
⁸ School of Science and Technology , Örebro University , SE-701 82 Örebro , Sweden.

PMID: 30717591
DOI: 10.1021/acs.jpclett.8b03711

Abstract

We investigate the magnetic and electronic properties of europium cyclooctatetraene (EuCot) nanowires by means of low-temperature X-ray magnetic circular dichroism (XMCD) and scanning tunneling microscopy (STM) and spectroscopy (STS). The EuCot nanowires are prepared in situ on a graphene surface. STS measurements identify EuCot as an insulator with a minority band gap of 2.3 eV. By means of Eu M_5,4 edge XMCD, orbital and spin magnetic moments of (-0.1 ± 0.3)μ_B and (+7.0 ± 0.6)μ_B, respectively, were determined. Field-dependent measurements of the XMCD signal at the Eu M₅ edge show hysteresis for grazing X-ray incidence at 5 K, thus confirming EuCot as a ferromagnetic material. Our density functional theory calculations reproduce the experimentally observed minority band gap. Modeling the experimental results theoretically, we find that the effective interatomic exchange interaction between Eu atoms is on the order of millielectronvolts, that magnetocrystalline anisotropy energy is roughly half as big, and that dipolar energy is approximately ten times lower.