Element-specific investigation of 4f -magnetism: graphene-covered surface alloys and sandwich-molecular nanowires

The precise control of the magnetic properties of 4f metals is not only crucial for many applications in our daily lives, like heavy-duty permanent magnets in generators and electric motors, but is also the key to realizing future nanosized and energy-efficient spintronic devices. In this work, we will contribute to this field with two different approaches.

By incorporating 4f metals into a long-range ordered two-dimensional iridium surface alloy, we provide a proof-of-concept system, that allows us to tailor its magnetic properties by graphene adsorption. Our combined theoretical and experimental approach reveals, that graphene adsorption selectively lifts the 4f atoms out of the surface alloy, leading to a drastic increase in electronic and magnetic anisotropy, which we studied by X-ray absorption spectroscopy and X-ray magnetic circular dichroic measurements. A combined theoretical approach based on ligand field multiplet theory and ab initio calculations allows us to precisely model these systems and provide a deeper understanding of the changes in the magnetic and electronic properties. Including a whole set of 4f metals into this system allows us to generalize the graphene-induced selective skyhook effect and provides us insides into the changes with changing 4f occupation. This set of electronically similar, but magnetically tunable 4f graphene-covered surface alloys could be used as substrates for future spintronic applications.

Such organometallic spintronic components, namely europium cyclooctatetraene nanowires, are studied in the second part. By probing the electronic and magnetic properties of these wires on various substrates, we revealed the influence of global orientation, electronic doping, and interaction with a magnetic substrate on these systems, especially the magnetic susceptibility and the ferromagnetic order. The variation of the organic ligands, as well as the 4f metal, provides further insides. The ”zero-dimensional” thulium cyclooctatetraene compounds however approach the limit of electronic and magnetic anisotropy and show strong evidence of significant interaction of the 4f shell with its local surrounding.


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