On the Electronic and Magnetic Properties of the ionic superatomic solid Ni$_{9}$Te$_{6}$(PEt$_{3})_{8}$C$_{60}$

We have carried out first principles electronic structure studies to examine the atomic structure, stability, and electronic and magnetic properties of the recently synthesized Ni$_{9}$Te$_{6}$(PEt$_{3})_{8}$C$_{60}$ ionic material consisting of Ni$_{9}$Te$_{6}$(PEt$_{3})_{8\, }$superatoms and C$_{60}$. It is shown that the PEt$_{3}$ ligands result in an internal coulomb well that lifts the quantum states of the Ni$_{9}$Te$_{6}$ cluster lowering its ionization potential to 3.39 eV thus creating a superatomic alkali motif. The metallic core has a spin magnetic moment of 5.3 \textmu $_{b}$ in agreement with experiment. The clusters are marked by low magnetic anisotropy energy (MAE) of 2.72 meV and a larger intra-exchange coupling exceeding 0.2 eV indicating that the observed paramagnetic behavior around 10K is due to superparamagnetic relaxations. The magnetic motifs separated by C$_{60}$ experience a weak superexchange that stabilizes a ferromagnetic ground state as observed around 2K. The calculated MAE is sensitive to the charged state that could account for the observed change in magnetic transition temperature with size of the ligands or anion.