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

Abstract

We investigate the magnetic and electronic properties of europium cyclooctatetraene nanowires (EuCot) by means of lowtemperature 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 a wide-band-gap semiconductor with a 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 M 5 edge show hysteresis for grazing x-ray incidence at 5 K, thus confirming EuCot as a ferromag-netic material. Our density functional theory 17 calculations reproduce the experimentally ob-18 served bandgap. Modelling the experimental 19 results theoretically, we find that the effective 20 interatomic exchange interaction between Eu 21 atoms is of the order of meV, that magne-22 tocrystalline anisotropy energy is roughly half 23 as big and that dipolar energy is approximately 24 ten times lower.

Two-Dimensional Magnets beyond the Monolayer Limit

“…Both temperature and magnetic field dependences of the magnetic moment in the Eu/Si(001) surface phases (Figure c and Supplementary Figure 6) reveal significant magnetic signals in the 2D and 1D ordered systems, unlike the irregular 2 × 3 reconstruction. The fact that 3 out of 4 Eu/Si(001) reconstructions exhibit nontrivial magnetism correlates with the general ability of Eu to form various 2D FM structures such as ML films of Eu/silicene, , Eu/germanene, and Eu/graphene, nanocarpets of Eu-cyclooctatetraene or the surface of EuIr 2 Si 2 . The Eu superstructures constitute a family which may be easier to expand (see below) than the families of layered 2D FM compounds like Cr trihalides , and rare-earth metalloxenes …”

Single-crystal graphene on Ir(110)

“…This observation implies directly the mobility of reaction intermediates to wire ends and the re-evaporation of the Cot excess at room temperature. This Based on the successful on-surface synthesis using the same parameters as for EuCot wire growth on Gr/Ir(111) [8,38], it is evident that also on Gr/Ir(110) the wires are bound through van der Waals interactions to the substrate. The upright standing aromatic Cot-dianions are in contact with Gr only through their peripheral H-atoms.…”

“…When Eu atoms and cyclooctatetreaene (Cot, C 8 H 8 ) molecules (eight-membered carbon rings) are combined in room temperature on-surface synthesis on Gr/Ir(111), Eu is evaporated onto the substrate in a background pressure of Cot, of which the excess re-evaporates at 300 K [8]. Because of van der Waals interaction between the wires, they interlock and form monolayer high, randomly oriented islands of parallel wires resulting in diffraction rings rather than spots in LEED [8,38]. The lack of island orientation was found not to depend on coverage.…”

“…In DFT calcuations naphthalene is used as a paradigm for an aromatic molecule to explore the anisotropic energy landscape of physisorption induced by the wave pattern. Based on these insights, unaxial alignment of sandwich-molecular wires during organometallic on-surface synthesis [8,38] is experimentally demonstrated. Inert single-crystal substrates are rare, but attractive for the growth of quasifreestanding 2D layers.…”

Prediction of a Nine−Membered Aromatic Heterocyclic 1,4,7−triazacyclononatetraenyl anion and its Sandwich Complexes with Divalent Lanthanides

“…[1−4] Besides, metallocenes play an important role in the development of new class of materials, associated with intriguing electronic and magnetic properties Recently a new surface−supported one−dimensional organometallic sandwich molecular nanowires associated with ferromagnetic insulator properties has been synthesized . Discovery of the first sandwich complex, viz., biscyclopentadienyl Iron [Fe(C 5 H 5 ) 2 ] (ferrocene) has provided an extensive series of breakthroughs in the field of organometallic chemistry …”