Iron porphyrin molecules on Cu(001): Influence of adlayers and ligands on the magnetic properties

Abstract

The structural and magnetic properties of Fe octaethylporphyrin (OEP) molecules on Cu(001) have been investigated by means of density functional theory (DFT) methods and X-ray absorption spectroscopy. The molecules have been adsorbed on the bare metal surface and on an oxygen-covered surface, which shows a √ 2 × 2 √ 2R45 • reconstruction. In order to allow for a direct comparison between magnetic moments obtained from sum-rule analysis and DFT we calculate the dipolar term 7 Tz , which is also important in view of the magnetic anisotropy of the molecule. The measured Xray magnetic circular dichroism shows a strong dependence on the photon incidence angle, which we could relate to a huge value of 7 Tz , e.g. on Cu(001) 7 Tz amounts to -2.07 µB for normal incidence leading to a reduction of the effective spin moment ms+7 Tz . Calculations have also been performed to study the influence of possible ligands such as Cl and O atoms on the magnetic properties of the molecule and the interaction between molecule and surface, because the experimental spectra display a clear dependence on the ligand, which is used to stabilize the molecule in the gas phase. Both types of ligands weaken the hybridization between surface and porphyrin molecule and change the magnetic spin state of the molecule, but the changes in the X-ray absorption are clearly related to residual Cl ligands.

Influence of ligands on the electronic and magnetic properties of Fe porphyrin in gas phase and on Cu(001)

“…This result is slightly different from previous observations for the same system, where the PW91 functional had been used instead of the PBE. 10 Both configurations have out of plane Fe d orbitals in the LUMO, which corresponds to the experimental findings in Ref. 10.…”

“…10 Both configurations have out of plane Fe d orbitals in the LUMO, which corresponds to the experimental findings in Ref. 10. However, from the x-ray absorption spectra (XAS) of Fe L 2,3 edge, it is not possible to distinguish between the d p and the d z 2 .…”

“…10 This might be an artefact of the D2 method, which tends to overbind, i.e., the resulting distance between the molecule and the substrate is too small. In order to correct this effect, we have performed calculations with the D3 method, 21 but have obtained quite similar results.…”

“…9 In the present work, we use Cu(001) as a substrate, which is assumed to interact less strongly with the molecules. 10 We have performed Density Functional Theory (DFT) calculations including van der Waals corrections of the adsorption of FeP with different axial ligands on Cu(001). The electronic and magnetic properties of the adsorbed systems are compared to our findings for the free molecules.…”

Surface Morphology of Fe(III)-Porphyrin Thin Layers as Characterized by Atomic Force Microscopy

“…There have been several fascinating studies of coupling between the porphyrin molecules and the thin layers of substrates [13][14][15][16][17]. Magnetic characteristics and the effect of external magnetic fields on molecules metalloporphyrin have been studied [18][19][20].Charge carrier mobility under the influence of a magnetic field in Hall effect configuration on porphyrin-based materials has also been observed [21][22][23][24][25][26][27].For the detection of neurotransmitters, graphite electrodes coated by electropolymerized porphyrins have been studied since1997 [6]. Fabrication of the solid state sensor by porphyrin derivatives on glass substrates for optochemical sensing of HCl gas has also been reported in 2012 [28].…”