Designing magnetic superatoms with large magnetic moments and great stabilities

Magnetic superatoms with high spin states are essentially in contrary to the superatom concept of closed electronic shells. The magnetic moments are usually results of the subtle competition between Hund's rule coupling and the Jahn–Teller distortion in high symmetry clusters. Even Hund's rule wins in some clusters due to favorable exchange splitting of the spin-up and -down orbitals, the ground state might be antiferromagnetic. Here, we investigate the electronic origin of the specific stabilities of the metallo-carbohedrenes M8C12 and their magnetic properties. The six C2 units in these tetrahedral structures can be regarded as acetylene-like C22− and the transition metal (TM) atoms need to donate 12 electrons accordingly. The local electronic repulsion in the TM atoms reduces considerably and the atomic d orbitals may be occupied in parallel. The ground states of Fe4Cu4C12 and Mn4M4C12 (M = Cu, Ag) have 16 and 20 unpaired electrons, respectively. Only Mn4Cu4C12 is ferromagnetic with a magnetic moment 20 μB, and the magnetic anisotropy energy is 0.010 eV.