Prof Arzhang Ardavan

Abstract:

Two different structural isomers of Nd@C82 have been isolated using two-stage high-performance liquid chromatography. Their molecular orbital structures have been studied by a combination of scanning tunneling microscopy (STM) and density functional theory (DFT). Matching filled and empty-states STM images to DFT calculations allowed us to distinguish directly between the two isomers on the surface. © 2005 Elsevier B.V. All rights reserved.

Abstract:

For the first time, two types of the metallofullerene Nd@C82 have been isolated and characterized. HPLC was used to isolate Nd@C 82(I, II). The two isomers were characterized by mass spectrometry and UV-Vis-NIR absorption spectroscopy. Nd@C82(I) was found to be similar in structure to the main isomer of other lanthanofullerenes such as La@C82, as was previously reported. We assign Nd@C82(I) to have a C2v cage symmetry. Nd@C82(II) showed a markedly different UV-Vis-NIR absorption spectrum to Nd@C82(I). Its spectrum is in good agreement with that of the minor isomer of metallofullerenes such as Pr@C82. We therefore assign Nd@C82(II) to have a C s cage symmetry. In contrast to other metallofullerenes, both isomers appear to be equally abundant. © 2005 American Institute of Physics.

Abstract:

We present numerical calculations of a tight-binding model applied to a finite square lattice in the presence of a perpendicular magnetic field. The persistent current associated with each eigenstate is calculated, the chirality of which is determined by whether the eigenstate exists within the bulk or localised to the edges of the lattice. This treatment allows us to extract oscillations in the magnetization, which are analogous to de Haas-van Alphen oscillations. We consider the influence of short range disorder and long range potential modulations on these systems.

Abstract:

We report millimetre-wave electron spin resonance (ESR) measurements on single crystals of the high-spin molecules Cr-10(OMe)(20)(O2CCMe3)(10) and Cr12O9(OH)(3)(O2CCMe3)(15) within a temperature range of 1.4 K to 50 K and in magnetic fields of up to 5 Tesla. In our experiments it is possible to vary the orientation of the magnetic field with respect to the crystal axes, and thus to study the ESR lineshapes as a function of both temperature and angle. Our results confirm that Cr-10(OMe)(20)(O2CCMe3)(10) behaves as a single-molecule magnet with S = 15 and D = -0.03 K, while Cr12O9(OH)(3)(O2CCMe3)(15) has S = 6 and D similar to 0.1 K. A comparison of the experimental spectra with numerical simulations gives good agreement at low temperatures. At higher temperatures, we observe a narrowing of the ESR spectrum that is not explained by simple models.