The nonlocal van der Waals density functional approach is applied to calculate the binding of graphene to Ir(111). The precise agreement of the calculated mean height h = 3.41  Å of the C atoms with their mean height h = (3.38±0.04)  Å as measured by the x-ray standing wave technique provides a benchmark for the applicability of the nonlocal functional. We find bonding of graphene to Ir(111) to be due to the van der Waals interaction with an antibonding average contribution from chemical interaction. Despite its globally repulsive character, in certain areas of the large graphene moiré unit cell charge accumulation between Ir substrate and graphene C atoms is observed, signaling a weak covalent bond formation.

The use of molecular spin state as a quantum of information for storage, sensing and computing has generated considerable interest in the context of next-generation data storage and communication devices 1, 2 , opening avenues for developing multifunctional molecular spintronics 3 . Such ideas have been researched extensively, using singlemolecule magnets 4, 5 and molecules with a metal ion 6 or nitrogen vacancy 7 as localized spin-carrying centres for storage and for realizing logic operations 8 . However, the electronic coupling between the spin centres of these molecules is rather weak, which makes construction of quantum memory registers a challenging task 9 . In this regard, delocalized carbon-based radical species with unpaired spin, such as phenalenyl 10 , have shown promise. These phenalenyl moieties, which can be regarded as graphene fragments, are formed by the fusion of three benzene rings and belong to the class of open-shell systems. The spin structure of these molecules responds to external stimuli 11, 12 (such as light, and electric and magnetic fields), which provides novel schemes for performing spin memory and logic operations. Here we construct a molecular device using such molecules as templates to engineer interfacial spin transfer resulting from hybridization and magnetic exchange interaction with the surface of a ferromagnet; the device shows an unexpected interfacial magnetoresistance of more than 20 per cent near room temperature. Moreover, we successfully demonstrate the formation of a nanoscale magnetic molecule with a well-defined magnetic hysteresis on ferromagnetic surfaces. Owing to strong magnetic coupling with the ferromagnet, such independent switching of an adsorbed magnetic molecule has been unsuccessful with single-molecule magnets 13 . Our findings suggest the use of chemically amenable phenalenyl-based molecules as a viable and scalable platform for building molecular-scale quantum spin memory and processors for technological development.The diversity and flexibility of molecular synthesis has given researchers ample freedom to design functional molecules for spintronics. These include molecular magnets 14 , spinfilter molecules 15 , spin-crossover molecules 16 , molecular batteries 17 , molecular conductors 10 , molecular switches 12 , and spacer layers for organic spin valves 18 and magnetic tunnel junctions 19,20 . Using such synthetic techniques, we have designed a neutral planar phenalenyl-based molecule, zinc methyl phenalenyl (ZMP, C 14 H 10 O 2 Zn; see Fig. 1a and Methods), that has no net spin. When these molecules are grown on a ferromagnetic surface, interface spin transfer causes a hybridized organometallic supramolecular magnetic layer to develop, which shows a large magnetic anisotropy and spin-filter properties 21 . This interface layer creates a spin-dependent resistance and gives rise to an interface magnetoresistance (IMR) effect.

By means of ab initio calculations and spin-polarized scanning tunneling microscopy experiments we show how to manipulate the local spin-polarization of a ferromagnetic surface by creating a complex energy dependent magnetic structure. We demonstrate this novel effect by adsorbing organic molecules containing π(pz)-electrons onto a ferromagnetic surface, in which the hybridization of the out-of-plane pz atomic type orbitals with the d-states of the metal leads to the inversion of the spin-polarization at the organic site due to a pz − d Zener exchange type mechanism. As a key result, we demonstrate that it is possible to selectively inject spin-up and spin-down electrons from the same ferromagnetic surface, an effect which can be exploited in future spintronic devices.PACS numbers: 68.43.Bc,71.15.Mb Combining molecular electronics with spintronics represents one of the most exciting avenues in building future nanoelectronic devices [1][2][3]. For example, widely used in spintronic applications, the spin valve [4] is a layered structure of two ferromagnetic electrodes separated by a nonmagnetic spacer to decouple the two electrodes and allows spin-polarized electrons to travel through it. The efficiency of a spin valve depends crucially on the spin injection into and spin transport throughout the nonmagnetic spacer. On one side, since organic molecules are made of light elements with weak spin-orbit coupling as C and H, their use as spacer materials is very promising for transport properties since the spin coherence over time and distance is much larger than in the conventional semiconductors present in today's devices [5][6][7]. On the other side, the spin injection is mostly controlled by the ferromagnetic-organic layer interface [8,9] which is responsible for the significant spin loss in devices [10]. Therefore, a large effort is made to control the electronic properties at the organic-magnetic interfaces and, in this context, the theoretical first-principles calculations represent an indispensable tool to understand and guide experiments toward more efficient devices.In this Letter we propose a simple way to manipulate the local spin-polarization of a ferromagnetic surface by flat adsorbing organic molecules containing π(p z )-electrons onto it. As a consequence, around the Fermi level an inversion of the local spin-polarization at the organic site occurs with respect to the ferromagnetic surface due to a complex energy-and spin-dependent electronic structure of the organic-metal interface. The interaction between the molecule and the ferromagnetic surface reveals a mechanism similar to the p z − d Zener exchange [11] and enables a selective control of electron injection with different spins [i.e. up(↑) or down(↓)] from the same ferromagnetic surface within a specific energy The pz atomic orbitals in the spin-up channel hybridize with the majority (spin-up) states of the Fe atoms forming bonding (at lower energies) and antibonding (at higher energies) states some of them being pushed above the Fermi level...

We investigate the spin-and energy dependent tunneling through a single organic molecule (CoPc) adsorbed on a ferromagnetic Fe thin film, spatially resolved by low-temperature spin-polarized scanning tunneling microscopy. Interestingly, the metal ion as well as the organic ligand show a significant spin-dependence of tunneling current flow. State-of-the-art ab initio calculations including also van-der-Waals interactions reveal a strong hybridization of molecular orbitals and surface 3d states. The molecule is anionic due to a transfer of one electron, resulting in a non-magnetic (S= 0) state. Nevertheless, tunneling through the molecule exhibits a pronounced spin-dependence due to spin-split molecule-surface hybrid states. [4,5]. However, detailed and quantitative access to different constituents of a single molecule is desirable, though challenging. Scanning tunneling microscopy (STM) is well established as a probe of a local spin [6][7][8][9][10][11][12][13] in an atomically well defined environment.Iacovita et al. recently performed a spin-polarized STM (SP-STM) study of a CoPc in contact with a ferromagnetic cobalt nano-island [14]. Stacking contrast, spin-dependent scattering, edge states, mesoscopic relaxations as well as the adsorbate induced modification create a complex environment [15] toward understanding the influence of the substrate on molecular magnetism. After careful selection of electronically equivalent Co nanoislands a ferromagnetic exchange interaction between the molecular spin and the cobalt lead was successfully deduced, both theoretically and experimentally.In this letter we demonstrate a significant spinpolarization for a CoPc molecule in contact with a ferromagnetic Fe thin film due to molecule-substrate hybridization even though the molecule loses its net spin. As confirmed by SP-STM, an energy/site-dependent spin polarization from inversion to amplification is resolved on the sub-molecular scale. State-of-the-art density functional theory (DFT), which includes the decisive role of van-der-Waals (vdW) interactions, reveals both the magnetic and electronic nature of the molecule coupled to the ferromagnetic substrate. Even though the net spin of the molecule is lost due to a transfer of one electron, spin-splitting is recovered through the local bonding of molecular orbitals with Fe 3d bands.Simulations were carried out in the DFT [16] formalism with a plane wave implementation as provided by the VASP code [17]. Pseudopotentials used were generated with the projector augmented wave method [18] by using the PBE generalized-gradient exchange-correlation energy functional [19] (GGA). A slab consisting of two Fe and three W atomic layers, with a (5×7) in-plane surface unit cell modeled the molecule-surface system. The kinetic energy cutoff of the plane waves was set to 500 eV while the Brillouin zone was sampled by the Γ point. Optimized molecule-surface geometries were obtained by relaxing all molecular degrees of freedom and those of the Fe overlayers by including long-range vdW intera...

Properties of many layered materials, including copper-and iron-based superconductors, topological insulators, graphite and epitaxial graphene, can be manipulated by the inclusion of different atomic and molecular species between the layers via a process known as intercalation. For example, intercalation in graphite can lead to superconductivity and is crucial in the working cycle of modern batteries and supercapacitors. Intercalation involves complex diffusion processes along and across the layers; however, the microscopic mechanisms and dynamics of these processes are not well understood. Here we report on a novel mechanism for intercalation and entrapment of alkali atoms under epitaxial graphene. We find that the intercalation is adjusted by the van der Waals interaction, with the dynamics governed by defects anchored to graphene wrinkles. Our findings are relevant for the future design and application of graphene-based nano-structures. Similar mechanisms can also have a role for intercalation of layered materials.

Using spin-polarized scanning tunneling microscopy and density functional theory, we have studied the structural and magnetic properties of cobalt-intercalated graphene on Ir(111). The cobalt forms monolayer islands being pseudomorphic with the Ir(111) beneath the graphene. The strong bonding between graphene and cobalt leads to a high corrugation within the Moiré pattern which arises due to the lattice mismatch between the graphene and the Co on Ir(111). The intercalation regions exhibit an out-of-plane easy axis with an extremely high switching field, which surpasses the significant values reported for uncovered cobalt islands on Ir(111). Within the Moiré unit cell of the intercalation regions, we observe a site-dependent variation of the local effective spin polarization. State-of-the-art first-principles calculations show that the origin of this variation is a site-dependent magnetization of the graphene: At top sites the graphene is coupled ferromagnetically to the cobalt underneath, while it is antiferromagnetically coupled at fcc and hcp sites.

Using the X-ray standing wave method, scanning tunneling microscopy, low energy electron diffraction, and density functional theory, we precisely determine the lateral and vertical structure of hexagonal boron nitride on Ir(111). The moiré superstructure leads to a periodic arrangement of strongly chemisorbed valleys in an otherwise rather flat, weakly physisorbed plane. The best commensurate approximation of the moiré unit cell is (12 × 12) boron nitride cells resting on (11 × 11) substrate cells, which is at variance with several earlier studies. We uncover the existence of two fundamentally different mechanisms of layer formation for hexagonal boron nitride, namely, nucleation and growth as opposed to network formation without nucleation. The different pathways are linked to different distributions of rotational domains, and the latter enables selection of a single orientation only.

We reveal for the first time through a theoretical first-principles study that the adsorption of a nonmagnetic π-conjugated organic molecule on a ferromagnetic surface locally increases the strength of the magnetic exchange interaction between the magnetic atoms binding directly to the molecule. This magnetic hardening effect leads to the creation of a local molecular mediated magnetic unit with a stable magnetization direction and an enhanced barrier for the magnetization switching as compared to the clean surface. Remarkably, such a hybrid organic-ferromagnetic system exhibits also a spin-filter functionality with sharp spin-split molecularlike electronic features at the molecular site.