Geometrical structure and spin order of Gd13 cluster

Ab initio prediction of the electronic, magnetic and topological properties of Ln2O3 clusters

The structural, electronic and magnetic properties of the lanthanide oxide Ln₂O₃ clusters, where Ln signifies lanthanides from La to Lu, have been calculated using spin-polarized density functional theory with the B3LYP hybrid functional. The intensities of ferromagnetic RKKY interaction are found comparable with that of antiferromagnetic superexchange interaction in Ce₂O₃ / Pr₂O₃ / Nd₂O₃ / Gd₂O₃ / Tb₂O₃ / Tm₂O₃ clusters, while the other Ln₂O₃ clusters prefer ferromagnetic states to antiferromagnetic states in energy, except nonmagnetic La₂O₃ and Lu₂O₃ clusters. The theoretical spin magnetic moments, calculated three-dimensional spin density maps and dipole moments of Ln₂O₃ clusters suggest that the induced polarizations of oxygen atoms in Sm₂O₃, Eu₂O₃ and Yb₂O₃ clusters remarkably lead to the elongated Ln-O bond lengths in these clusters. The partial density of states of Ln₂O₃ clusters reveals that Sm³⁺ /Eu³⁺ /Yb³⁺ ions are distinctive from other Ln³⁺ ions in that their Ln-4f electrons are strongly hybrid with O-2 p electrons. The topological analysis of the electron density was also performed with quantum theory of atoms in molecules, which indicates the ionic Ln-O bonds have partial covalent characteristics.

Magnetism and exchange interaction of small rare-earth clusters; Tb as a representative

Here we follow, both experimentally and theoretically, the development of magnetism in Tb clusters from the atomic limit, adding one atom at a time. The exchange interaction is, surprisingly, observed to drastically increase compared to that of bulk, and to exhibit irregular oscillations as a function of the interatomic distance. From electronic structure theory we find that the theoretical magnetic moments oscillate with cluster size in exact agreement with experimental data. Unlike the bulk, the oscillation is not caused by the RKKY mechanism. Instead, the inter-atomic exchange is shown to be driven by a competition between wave-function overlap of the 5d shell and the on-site exchange interaction, which leads to a competition between ferromagnetic double-exchange and antiferromagnetic super-exchange. This understanding opens up new ways to tune the magnetic properties of rare-earth based magnets with nano-sized building blocks.

Monoxides of small terbium clusters: a density functional theory investigation

To investigate the effect of oxygen atom on the geometrical structures, electronic, and magnetic properties of small terbium clusters, we carried out the first-principles calculations on TbnO (n = 1-14) clusters. The capping of an oxygen atom on one trigonal-facet of Tbn structures is always favored energetically, which can significantly improve the structural stability. The far-infrared vibrational spectroscopies are found to be different from those of corresponding bare clusters, providing a distinct signal to detect the characteristic structures of TbnO clusters. The primary effect of oxygen atom on magnetic properties is to change the magnetic orderings among Tb atoms and to reduce small of local magnetic moments of the O-coordinated Tb atoms, both of which serve as the key reasons for the experimental magnetic evolution of an oscillating behavior. These calculations are consistent with, and help to account for, the experimentally observed magnetic properties of monoxide TbnO clusters [C. N. Van Dijk et al., J. Appl. Phys. 107, 09B526 (2010)].