Magnetism of electrons in atoms and superatoms

The quantum states of electrons in small symmetric metallic clusters are grouped into shells similar to the electronic shells in free atoms, leading to the conceptual basis for defining superatoms. The filling of the electronic shells in clusters, however, do not follow Hund's rule and usually result in non-magnetic species. It is shown that by embedding a transition metal in group II atoms, one can stabilize superatoms with unpaired electronic supershells. We demonstrate this intriguing effect through electronic structure studies of MnSr_n (n = 6-12) clusters within first principles generalized gradient calculations. The studies identify an unusually stable magnetic MnSr₉ species with a large exchange splitting of 1.82 eV of the superatomic D-states. It is shown that the exchange split d-states in the Mn atom induce exchange splitting in S and D superatomic shells because of the hybridization between orbitals of selected parity. The magnetic MnSr₉ cluster with 25 valence electrons has filled 1S², 1P⁶, 1D¹⁰, 2S² shells, making it highly stable, and an open shell of 5 unpaired D electrons breeding the magnetic moment. The stable cluster is resistant to collapse as two motifs are united to form a supermolecule.