On the Existence of Designer Magnetic Superatoms

Abstract

The quantum states in small, compact metal clusters are bunched into electronic shells with electronic orbitals resembling those in atoms, enabling classification of stable clusters as superatoms. The filling of superatomic orbitals, however, does not generally follow Hund's rule, and it has been proposed that magnetic superatoms can be stabilized by doping simple metal clusters with magnetic atoms. Here, we present evidence of the existence of a magnetic superatom and the determination of its spin moment. Our approach combines first principles studies with negative ion photoelectron experiments and enables a unique identification of the ground state and spin multiplicity. The studies indicate VNa 8 to be a magnetic superatom with a filled d-subshell and a magnetic moment of 5.0 μ B . Its low electron affinity is consistent with filled subshell and enhanced stability. The synthesis of this species opens the pathway to investigate the spin-dependent electronics of the new magnetic motifs.

The role of TM’s (M’s) d valence electrons in TM@X12 and M@X12 clusters

“…The imaginary frequencies of all clusters are zero (in Table I), which ensures each structure gained to be an equilibrium structure. As shown in Table I, E HOMS -E HOMO is not included in the calculations of M@C 60 clusters, because they are not unreasonable structures, and can not also be viewed as superatomic atoms owe to their negative embedding energies (-0.38, -0.90, -0.83 eV for Zn@C 60 , Cd@C 60 and Hg@C 60 clusters, respectively) and larger R shell (3. 12 cluster, the R shell (3.08 Å) obviously less than the sum of the Van Waals radii of Mn and Sn atoms (1.37+2.17=3.54 Å), and the embedding energy (6.89 eV) significantly bigger than the binding energy (2.64 eV), these results suggest that Mn atom is strongly bonded with outer Sn atom, ie., can be attractively embedded to the centre of Sn 12 , which agrees well with previous studies on the same structure. 7,8,14 The similar analyses on all TM@X 12 and M@X 12 clusters, indicate that TM or M atoms can be attractively embedded to the centre of X 12 too, and suggest that their structures also are extremely stable.…”

“…The representative structures of TM@X 12 , M@X 12 and M@C 60 clusters are showed in Fig. 1, where a TM or M atom is embedded in the center of X 12 cage to give an corresponding icosahedral structure.…”

“…Similarly, a M atom is also implanted in the center of C 60 cage forming a sphere in I h symmetry. The geometrical optimizations are performed through employing the DMOL simulation program package, 20 using the effective core potential (ECP), 21,22 double-numerical basis sets with p-polarization function (DNP), and PW91 exchange correlation potential in the generalized gradient approximation (GGA), 21,23 to gain the magnetic ground state of TM@X 12 , M@X 12 and M@C 60 clusters, which is more practical and effective than other software (such as Gaussian 09) by turning on spin unrestricted of the DMOL simulation program package implanted in materials studio (MS). Nevertheless, in order to further confirm the magnetic ground state obtained, other spin multiplicities of the clusters are further considered by alternating the values of the gained spin multiplicity, and the energies of each cluster with different spin multiplicities also are compared.…”

“…1 Based on the extraordinary stability of superatoms, their optical, dielectric, magnetic, and catalytic properties have been studied in previous reports. 1,3,4 For instance, Zn@Ge 12 and Cd@Sn 12 clusters with a large HOMO-LUMO gap of about 2 eV may be used to assemble optoelectronic materials; 5 accordingly, MnCa n (n=6-15) clusters, 6 Mn@Sn 12 cluster 4,7,8 MnSr 9 cluster, 9 TcMg 8 cluster 10 and V-alkali clusters (VLi 8 , 11 VNa 8 12 and VCs 8 13 ) magnetic superatoms show a large spin magnetic moment of 5 µ B , where the superior stability of Mn@Sn 12 cluster 4,14 was confirmed in experiments. So far, it is generally accepted that the spin magnetic moment of magnetic superatoms is offered by atomic d-state electrons (or superatomic D states) localized on TM sites, while its superatomic stability is provided via the delocalized s, p-valence electrons of metal atoms fully occupied diffuse superatomic S, P states.…”

Evolution of lithium clusters to superatomic Li3O+

“…Thus, the Li 3 O + cluster contains 8 valence electrons and corresponds to a magic species in accordance with the 18-electron rule 23,24 . Clearly the closed-shell electron structure is classified as a superatom that consists of specific atoms that share electrons but mimics the chemical behavior of other elements [25][26][27][28][29][30] . However, unlike previous reports of magnetic lithium superatoms that were stretched in three dimensions 31 , Li 3 O + possessed a planar structure while maintaining its superatomic properties.…”