Applications like giant magnetoresistance (GMR) read-heads and magnetic random-access memory (MRAM) rely on so-called spin transport electronics or ‘spintronics’, where the electron spin rather than the charge is employed to carry information. The possibility to use organic compounds as spintronics materials opens new opportunities, as they allow precise modification of there properties by chemical substitution. To advance towards versatile magnetic materials with decreasing domain and layer dimensions, the understanding of local magnetic coupling in molecular monolayers is of utmost importance.

The main aim of this research project is to investigate the magnetic coupling between the adsorbed organic molecules and ferromagnetic substrate using the X-ray magnetic circular dichroism (XMCD) technique.

Our pioneering XMCD experiments with manganese (III)-tetraphenylporhyrin chloride (MnTPPCl) molecules on cobalt films provided the first clear evidence for a magnetic coupling between the MnTPPCl molecules and the ferromagnetic substrate [1].
In the recent publication by Wende et al.[2] the magnetic coupling for Fe porphyrin molecules and ferromagnetic cobalt films with in plane easy axis of magnetisation has been confirmed as well as for nickel films with out of plane easy axis magnetisation direction.

We characterize the geometrical and electronic structure of in-situ prepared samples by using Scanning Tunneling Microscopy (STM) and X-ray Photoelectron spectroscopy (XPS). The molecular orientation is investigated by angle-dependent Near-Edge X-ray Absorption Fine-structure Spectroscopy (NEXAFS).

In the current project the adsorption site dependence of the magnetic coupling of molecular magnets to perpendicularly magnetized Co(0001) single crystal substrates and in-plane magnetized ultra-thin Co(0001) films on W(110) will be exploited by combination of XMCD and molecular resolution STM. This will provide us with a deeper insight into the mechanism of the magnetic coupling of paramagnetic organic molecules on a ferromagnetic metallic substrate and may provide new insight into these effects which are referred to as organic spintronics.

References

[1] A. Scheybal et al., Chem. Phys. Lett. 411 (2005) 214.
[2] H. Wende et al., Nature Materials 2007.

Contact
Dr. Timur Kim: timur.kimpsi.ch
Kathrin Müller:kathrin.muellerpsi.ch
Dr. T.A. Jung: thomas.jungpsi.ch

Financial support:
PSI, National Center for Compentence in Research, Nanosciences of the Swiss National Science Foundation, Swiss National Science Foundation through their Division 2 for Basic Research