Professor Stephen Blundell

Abstract:

muSR can be applied to the study of various dynamical processes in polymers. These processes may relate to carrier motion, as in studies of conducting polymers which make use of muon generated polarons to measure carrier diffusion rates. Alternatively the processes of interest may be related to the structural dynamics of the polymer, which can show dramatic changes around the glass transition temperature. We report here examples of the use of muSR to study the muon states and muon mobility in the polymers polyethylene and polytetrafluoroethylene, where coherent FmuF precession signals have been observed. In the case of polystyrene, muon radical states formed on the phenyl ring have been used to make a detailed study of the dynamical freezing and onset of static disorder that accompanies the glass transition. Finally, we report a study of polaron diffusion in two polyphenylenevinylene conducting polymers. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract:

We present the results of recent muSR experiments on a variety of novel organic and molecular magnetic systems. Muons are sensitive to local static fields and magnetic fluctuations, but can probe much more than just the onset of long-range magnetic order. We review our work on nitronyl nitroxide organic ferromagnets and anti ferromagnets. We describe a muon study of the spin-crossover phenomenon which has been studied in Fe(PM-PEA)(2)(NCS)(2), and which shows Gaussian and root-exponential muon relaxation in the high-spin and low-spin phases, respectively. Experiments on a disc-shaped molecular complex containing Fe-19 (with spin 31/2) reveal the effects of quantum tunneling of magnetization and allow an estimate of the quantum tunneling rate. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract:

We present the results of zero-held mu(+)-SR measurements on CoCO3 and NiCO3. Both compounds are rhombohedral antiferromagnets which exhibit a spontaneous weak magnetisation below 22.2 and 17.2 K, respectively. This arises due to an anisotropic superexchange (Dzyaloshinsky-Moriya) interaction. We have studied the temperature dependence of the internal field in the ordered state and the magnetic fluctuations in the paramagnetic state. We describe the possible muon-site obtained from dipolar-field calculations. (C) 2002 Elsevier Science B.V. All rights reserved.