Professor Stephen Blundell

Abstract:

The muon is a valuable probe of spin excitations in polymers, as the muon implantation process itself generates a lest excitation whose dynamical properties can be studied via the evolution of the muon spin polarisation. We report here studies on undoped polyaniline in its emeraldine base form (PANI:EB). Characteristic field dependences and cutoff frequencies for the muon spin relaxation are observed which are related to the spin diffusion. One-dimensional diffusion is seen at low temperatures and at short probe times. The on chain diffusion is observed to have a weak metallic temperature dependence whereas the interchain diffusion is strongly activated and phenyl ring rotations are seen to have an important effect on the diffusion processes.

Abstract:

The crystallography and electronic properties of the Ln(2-x)Sr(1+x)Mn(2)O(7) manganese oxides adopting the n = 2 Ruddlesden-Popper (RP) structure are discussed, focusing on the structural phase diagrams and electronic properties in the vicinity of the Mn + 3.5 oxidation slate and in particular the ease of synthesis of single phases of these materials.

Abstract:

We report the results of magnetization, susceptibility and muon spin rotation/relaxation (mu SR) measurements and crystal structure analyses of the organic neutral and ion radicals based on nitronyl nitroxide. Magneto-structural correlations in naphthyl and quinolyl nitronyl nitroxides, some of which exhibit ferromagnetic intermolecular interactions, are discussed in terms of intermolecular and interatomic contacts. The temperature dependence of the paramagnetic susuceptibility of sodium 2-sulfonatofuryl nitronyl nitroxide and 2-carboxyfuryl nitronyl nitroxide are interpreted in terms of a combination of ferromagnetic and antiferromagnetic interactions. Of the organic radicals exhibiting ferromagnetic intermolecular interactions, magnetic transitions in the zero-field muon spin relaxation are observed in l-naphthyl and p-cyanophenyl nitronyl nitroxide below 0.10 and 0.17 K, respectively.

Abstract:

Ferromagnetism has been observed in a family of organic molecular crystals based on the nitronyl nitroxide radical. We present the results of mu SR experiments on a number of nitronyl nitroxide compounds. The zero-field spin precession of muons implanted in diamagnetic states can be used to follow the magnetic order parameter as a function of temperature. Five of the materials studied show magnetic transitions, although the transition temperature and the nature of the magnetic ground state in each case are quite different. mu SR can be used to study these ground states and thus help to relate the observed magnetic properties to the crystal structure of each material.