Ni9Te6(PEt3)8C60 Is a Superatomic Superalkali Superparamagnetic Cluster Assembled Material (S3-CAM)

First-principles theoretical studies enable an electronic and magnetic characterization of the recently synthesized Ni9Te6(PEt3)8C60 ionic material consisting of Ni9Te6(PEt3)8 superatoms and C60. The PEt3 ligands are shown to create an internal coulomb well that lifts the quantum states of the Ni9Te6 cluster, lowering its ionization potential to 3.39 eV thus creating a superalkali motif. The metallic core has a spin magnetic moment of 5.3 μB 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 C60 experience a weak superexchange that stabilizes a ferromagnetic ground state as observed around 2 K. 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.