Inferring the Dy-N axis orientation in adsorbed DySc2N@C80 endofullerenes by linearly polarized x-ray absorption spectroscopy

Endofullerene DySc2N@C80 is a single-molecule magnet with a large magnetic anisotropy and high blocking temperature, which is promising for nanomagnetic applications. As the easy axis of magnetization coincides with the Dy-N bond direction, it is important to understand the structure of the DySc2N unit in the fullerene cage and to control the orientation of the molecules. Here we report on the experimental determination of Dy-N axis by x-ray absorption spectroscopy (XAS) with linear polarized light at the Dy-M-4,M-5 white lines. DySc2N@C80 molecules were adsorbed on a Pt(111) surface and XAS was performed as a function of temperature in the range between 35 and 300 K. The M-5/M-4 branching ratio shows a clear and reversible variation with temperature which can be explained, on the basis of a thermodynamic model, by a change of average orientation of the molecules with temperature. The XAS spectra are well reproduced by ligand field multiplet calculations. It is shown that the angle between the magnetization (Dy-N) axis and the surface plane can be directly inferred from the XAS spectra with in-plane polarization by comparison with calculated spectra. It is found that the endohedral unit is randomly oriented at room temperature but tends towards orientation parallel to the surface at low temperature, indicating a weak but non-negligible interaction between the endohedral units and the metal surface.

Automated summary

This study experimentally determined the Dy-N axis by X-ray absorption spectroscopy (XAS) and found that the orientation of DySc2N@C80 molecules on a Pt(111) surface undergoes reversible changes with temperature. The results showed that the endohedral unit is randomly oriented at room temperature but tends to be parallel to the surface at low temperatures.