Investigating magneto-chemical interactions at molecule-substrate interfaces by X-ray photo-emission electron microscopy

The magneto-chemical interaction of spin-bearing molecules with substrates is interesting from a coordination chemistry point of view and relevant for spintronics. Unprecedented insight is provided by X-ray photo-emission electron microscopy combined with X-ray magnetic circular dichroism spectroscopy. Here the coupling of a Mn-porphyrin ad-layer to the ferromagnetic Co substrate through suitably modified interfaces is analyzed with this technique

Highly Stereospecific On‐Surface Dimerization into Bishelicenes: Topochemical Ullmann Coupling of Bromohelicene on Au(111)

The on‐surface dimerization into bis(hexahelicene) on a gold(111) surface has been studied by means of scanning tunneling microscopy and time‐of‐flight secondary mass spectrometry. C−C Ullmann coupling of (rac)‐2‐bromo‐hexahelicene leads to formation of the (M,M)‐ and (P,P)‐diastereomers of 2,2’‐bis(hexahelicene), whilst formation of the (M,P)‐diastereomer is not observed. Upon cooling, the bis(hexahelicene) aggregates into an ordered two‐dimensional lattice with partly randomly distributed enantiomers. The highly specific diastereomeric coupling is explained by the surface alignment of educt in combination with the strong steric overcrowding in a possible surface‐confined (M,P)‐product

Magnetic exchange coupling of a synthetic Co(II)-complex to a ferromagnetic Ni substrate

On-surface assembly of a spin-bearing and non-aromatic porphyrin-related synthetic Co(II)-complex on a ferromagnetic Ni thin film substrate and subsequent magnetic exchange interaction across the interface were studied by scanning tunnelling microscopy (STM), X-ray absorption spectroscopy (XAS), X-ray magnetic circular dichroism (XMCD) and density functional theory +U (DFT + U) calculations

Covalent assembly of a two-dimensional molecular ‘‘sponge’’ on a Cu(111) surface:Confined electronic surface states in open and closed pores

We present a new class of on-surface covalent reactions, formed between diborylene-3,4,9,10-tetraaminoperylene and trimesic acid on Cu(111), which gives rise to a porous 2D-'sponge'. This aperiodic network allowed the investigation of the dependence of electron confinement effects upon pore size, shape and even in partial confinement

Superlattice of Single Atom Magnets on Graphene

Regular arrays of single atoms with stable magnetization represent the ultimate limit of ultrahigh density storage media. Here we report a self-assembled superlattice of individual and noninteracting Dy atoms on graphene grown on Ir(111), with magnetic hysteresis up to 5.6 T and spin lifetime of 1000 s at 2.5 K. The observed magnetic stability is a consequence of the intrinsic low electron and phonon densities of graphene and the 6-fold symmetry of the adsorption site. Our array of single atom magnets has a density of 115 Tbit/inch(2), defined by the periodicity of the graphene moire pattern

The Role of the Magnetic Anisotropy in Atomic-Spin Sensing of 1D Molecular Chains

One-dimensional metal-organic chains often possess a complex magnetic structure susceptible to be modified by a alteration of their chemical composition. The possibility to tune their magnetic properties provides an interesting playground to explore quasiparticle interactions in low-dimensional systems. Despite the great effort invested so far, a detailed understanding of the interactions governing the electronic and magnetic properties of the low-dimensional systems is still incomplete. One of the reasons is the limited ability to characterize their magnetic properties at the atomic scale. Here, we provide a comprehensive study of the magnetic properties of metal-organic one-dimensional (1D) coordination polymers consisting of 2,5-diamino-1,4-benzoquinonediimine ligands coordinated with Co or Cr atoms synthesized in ultra-high vacuum conditions on a Au(111) surface. A combination of an integral X-ray spectroscopy with local-probe inelastic electron tunneling spectroscopy corroborated by multiplet analysis, density functional theory, and inelastic electron tunneling simulations enable us to obtain essential information about their magnetic structure, including the spin magnitude and orientation at the magnetic atoms, as well as the magnetic anisotropy.Comment: 35 pages, 8 Figures, 3 table

Magnetic properties of single rare-earth atoms on graphene/Ir(111)

We employed x-ray absorption spectroscopy and x-ray magnetic circular dichroism to study the magnetic properties of single rare-earth (RE) atoms (Nd, Tb, Dy, Ho, and Er) adsorbed on the graphene/Ir(111) surface. The interaction of RE atoms with graphene results for Tb in a trivalent state with 4fn-1 occupancy, and in a divalent state with 4fn occupancy for all other studied RE atoms (n corresponds to the 4f occupancy of free atoms). Among the studied RE on graphene/Ir(111), Dy is the only one that shows magnetic hysteresis and remanence at 2.5 K. By comparing measured spectra and magnetization curves with multiplet calculations, we determine the energy diagram of the magnetic states and show for each element the magnetization reversal process that determines the timescale of its magnetic bistability. © 2018 American Physical Societ