X-Ray Magnetic Circular Dichroism and Resonant Photomission ofV(TCNE)xHybrid Magnets

Abstract

Thin films of V(TCNE)x were deposited in ultrahigh vacuum using a film growth technique based on in situ chemical vapor deposition of tetracyanoethylene, TCNE, and bis-benzene vanadium, V(C6H6)2. The in situ preparation method enabled, for the first time, experimental analysis of oxygen-free films. X-ray magnetic circular dichroism measurements recorded at the V L(2,3) edge confirmed room temperature magnetic ordering. A combination of conventional photoelectron spectroscopy (PES) and resonant photoemission (RPE) measured at the V L3 edge shows that the highest occupied electronic state is V(3d) derived. The rearrangements of the TCNE- related valence electronic states observed in PES and the evidence of V(3d) and TCNE- pi(pi*) orbital overlap contained in RPE spectra, indicate that strong, covalent type bonding occurs between the vanadium and the TCNE molecules.

The unoccupied electronic structure of the semi-conducting room temperature molecular magnet V(TCNE)2

“…V(TCNE) x thin films were prepared in room temperature on sputter-cleaned gold substrates using a custom-built UHV-compatible deposition source based on chemical vapor deposition of bis(benzene)vanadium and tetracyanoethylene [13]. The background pressure in the preparation chamber was 10 -8 mbar.…”

“…Though the magnetic and electric (transport) response of V(TCNE) x has been characterized [8,11], the electronic structure of the material was until recently unknown [12][13][14]. This has greatly hampered the development of this class of magnets since knowledge about the frontier occupied and unoccupied molecular orbitals are of crucial importance to the electronic and magnetic properties.…”

“…The first results on the occupied electronic structure were obtained from a study of the model compound Rb(TCNE) [12] and have been compared with results on V(TCNE) x films that were prepared by a recently developed in-situ CVD method, enabling for the first time preparation and characterization of oxygen-free V(TCNE) x films [13]. The studies showed that there are strong hybridization between the vanadium and the TCNE in the occupied electronic structure.…”

“…As a result of the un-known physical structure of V(TCNE) x , theoretical calculations of the V(TCNE) x electronic structure have been impossible, but by using a model system of V(TCNE) x , namely alkali-doped TCNE, we have been able to partially circumvent this problem and theoretical results of alkali-doped TCNE have proven valuable in the interpretation of the experimental photoelectron spectroscopy (PES) and near edge x-ray absorption fine structure (NEXAFS) spectra of alkali-doped TCNE as well as of the more complex V(TCNE) x [12][13][14]. The first results on the occupied electronic structure were obtained from a study of the model compound Rb(TCNE) [12] and have been compared with results on V(TCNE) x films that were prepared by a recently developed in-situ CVD method, enabling for the first time preparation and characterization of oxygen-free V(TCNE) x films [13].…”

“…Development of chemical vapor deposition (CVD) fabrication techniques has however improved stability and reproducibility of the material [13][14][15][16][17]. An extended x-ray absorption fine structure (EXAFS) study has probed the local structure of the compound, showing that the vanadium ion coordinates to about six nitrogen atoms, most likely in a slightly distorted octahedral environment, each with an average distance in room temperature of 2.084(5) Å [18].…”