Professor Stephen Blundell

Abstract:

We report temperature dependent millimetre-wave spectroscopic experiments on single crystals of the organic molecular magnet 2-benzimidazolyl nitronyl nitroxide, in the range 1.4-100 K. This organic radical shows quasi one-dimensional (1-d) ferromagnetic intermolecular interactions with the intrachain exchange coupling constant J/k(B) = +22 K and interchain coupling constant J'/k(B) = 0.24 K. The linewidth of the electron spin resonance at low temperatures was seen to be considerably broadened as compared to that at higher temperatures. This is consistent with the low dimensional behaviour of the linewidth predicted theoretically. We also see a shift in resonance field at low temperatures. We also present the results of angular dependence experiments carried out at temperatures of 1.4 and 50 K, and frequency dependence experiments at 1.4 and 50 K. (c) 2005 Elsevier Ltd. All rights reserved.

Abstract:

We report the results of a muon spin rotation study on electron-doped chromium sulfides, Cr2S3-x, with 0≤x≤0.08. Two muon-spin precession frequencies are observed in each sample, corresponding to two distinct stopping sites. We show that even a small amount of electron doping, induced by sulfur deficiency, causes a drastic change in the magnetic properties. © 2005 The American Physical Society.

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.