Electronic structure, vibrational stability, and predicted infrared-Raman spectra of the As 20 , As @ Ni 12 , and As @ Ni 12 @ As 20 clusters Structure and stability of endohedral fullerene Sc 3 N@C 80 were studied by temperature-dependent Raman and infrared spectroscopy as well as by quantum-chemical ͓density-functional-based tight-binding͔ calculations. The material showed a remarkable thermal stability up to 650 K. By both theory and experiment, translational and rotational Sc 3 N modes were found. These modes give a direct evidence for the formation of a Sc 3 N-C 80 bond which induces a significant reduction of the ideal I h -C 80 symmetry. From their splitting pattern a crystal structure with more than one molecule in the unit cell is proposed. According to our results: ͑i͒ a significant charge transfer from the Sc 3 N cluster to the C 80 cage; ͑ii͒ the strength of three Sc-N bonds; ͑iii͒ the chemical bond between triscandium nitride cluster and C 80 cage; and ͑iv͒ a large HOMO-LUMO gap are responsible for the high stability and abundance of Sc 3 N@C 80 .

It is demonstrated by means of density functional and ab-initio quantum chemical calculations, that transition metal -carbon systems have the potential to enhance the presently achievable area density of magnetic recording by three orders of magnitude. As a model system, Co 2 -benzene with a diameter of 0.5 nm is investigated. It shows a magnetic anisotropy in the order of 0.1 eV per molecule, large enough to store permanently one bit of information at temperatures considerably larger than 4 K. A similar performance can be expected, if cobalt dimers are deposited on graphene or on graphite. It is suggested that the subnanometer bits can be written by simultaneous application of a moderate magnetic and a strong electric field. PACS numbers: 31.15.es, 75.30.Gw, 75.75.+a Keywords: applications of density functional theory, magnetic anisotropy, magnetic properties of nanostructures 1 Long-term magnetic data storage requires that spontaneous magnetization reversals should occur significantly less often than once in ten years. This implies that the total magnetic anisotropy energy (MAE) of each magnetic particle should exceed 40 kT , 1 where k is the Boltzmann constant and T is the temperature. Among the elemental ferromagnets (Fe, Co, Ni, and Gd), cobalt metal shows the highest MAE, about 0.06 meV per atom in the hexagonal close packed structure. Thus, Co is the main ingredient of magnetic data storage materials at present. At room temperature, data loss due to fluctuations is avoided, if a Co grain contains not less than 40 k · 300 K/0.06 meV ≈ 15,000 atoms. In fact, the grain diameter of contemporary Co(Cr,Pt,SiO 2 ) recording media is close to 8 nm, each grain containing about 50,000 atoms and each bit being composed of some dozen grains.2 The grain size could be considerably reduced by using the intermetallic compounds FePt or CoPt with record MAE of almost 1 meV per atom in their structurally ordered L1 0 bulk phase. It is, however, hard to achieve the required ordered structure in nano-particles. 3Obviously, a further reduction of the bit size is primarily limited by the value of MAE per atom. Recent efforts to enhance this value were focused on single atoms or small clusters deposited on the surface of heavy metals. This approach combines two ideas: 4 Firstly, the magnitude of MAE is related to the size of the orbital moments. The latter are quenched for highly coordinated atoms but can be large if the coordination is low. Secondly, the magnitude of MAE is related to the strength of spin-orbit coupling which grows with atomic number. Considerable progress was achieved in this way by deposition of single Co atoms on a Pt surface, yielding a record MAE of 9 meV per Co atom. 5 Unfortunately, clusters of several Co atoms on Pt show a much smaller MAE per atom, roughly inversely proportional to the number of atoms. 5More recently, the magnetic properties of transition metal dimers came into the focus of interest. 6,7,8,9 Isolated magnetic dimers are the smallest chemical objects that possess a magnetic a...

The electronic structure of small fullerenes determined experimentally by anion photoelectron spectroscopy is compared with calculations. A huge mass signal and a large gap of 1.3 eV comparable to the gap of C 70 have been found for C 32 , indicating that this cluster is the most stable fullerene below C 60. Also C 36 , C 44 , and C 50 exhibit large gaps and surprisingly high stabilities. The criteria for the selection of clusters sufficientl stable to form a cluster material are discussed.

We report the observation of quantized rotational states of a diatomic C2 unit in solid endohedral fullerene C(2)Sc(2)@C(84). The rotational transitions induce a periodic line pattern in the low energy Raman spectrum. The rotational constant B and the C-C distance were found to be 1.73 cm(-1) and 0.127 nm, respectively. Density functional calculations revealed an intrinsic rotational barrier of the order of only a few meV for the C2 unit. The Schrödinger equation involving the potential barrier was solved and the Raman tensor matrix elements were calculated, yielding good quantitative agreement with the experiment. To our best knowledge this is the first intrinsic rotational spectrum of a diatomic plane molecular rotor.

Ionization energies of the higher fullerenes C n (n ) 70-106) were measured by means of the ionmolecular equilibria-Knudsen cell mass spectrometry method. The obtained values were found to decrease with the size, going from IE(C 70 ) ) 7.36 eV down to IE(C 106 ) ) 6.92 eV, with unexpectedly low IE(C 74 ) ) 7.13 eV. A good correlation of the experimental results with the theoretical values is demonstrated. A simple model describing the ionization properties dependence from the fullerene size is proposed.