Magnetism of molecules on metal and superconducting surfaces

B. W. Heinrich

Institut für Experimentalphysik, Freie Universität Berlin, Germany

E-mail: bheinrich@zedat.fu-berlin.de

 

Atomic-size magnetic structures on surfaces are the basic playground to study magnetism in reduced dimensions. At such small scales, the magnetic properties do not only rely on the chemical nature, but also fundamentally on the interactions with the surrounding. Scanning tunneling microscopy and spectroscopy provide a versatile tool to unveil this influence of the structure on magnetic properties of individual atoms and molecules.

Here we will focus on paramagnetic metal-organic complexes adsorbed on metallic and superconducting surfaces. In a first example, we will show that the lifetime of excited spin states in iron- octaethylporphyrin-chloride is orders of magnitude longer when the molecule is adsorbed on a superconductor as compared to a normal metal substrate [1]. We ascribe this increase in spin relaxation time to the superconducting energy gap at the Fermi level, which prohibits efficient pathways of energy quenching into the substrate. Further, we manipulate the magnetic anisotropy of individual iron-porphyrins by a reversible change of the ligand field using the tip of the STM.

In a last experiment, we study the influence of the organic ligand on the interaction between the transition metal ion and the substrate. Inducing an on-surface ligand reaction, we increase the coupling to the substrate as evidenced by changes of the magnetic fingerprint in dI/dV spectroscopy.   

References

       [1]         B. W. Heinrich et al., Nature Phys. 9, 765 (2013).

       [2]         B. W. Heinrich et al., Nano Lett. 13, 4840 (2013).