P.A. Pattenden
University of Oxford
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by P.A. Pattenden.
Journal of Physics: Condensed Matter | 1994
P Bowmar; W. Hayes; Mohamedally Kurmoo; P.A. Pattenden; Mark A. Green; Peter Day; K Kikuchi
We describe results of Raman and infrared (IR) studies of single crystals of pure C60, CS2 solvated C60 (C601.5CS2), (BEDT-TIF)2 C60 (BEDT-TIF or ET is bis(ethylenedithio)tetrathiafulvalene) and C70. We find that changing the crystalline environment of C60 has little effect upon the vibrational frequencies of the intramolecular vibrations but has some effect on relative intensities of peaks. By comparing our IR and Raman spectra using the published inelastic neutron scattering and surface enhanced Raman data we have been able to identify the complete set of 46 fundamental intramolecular vibrational frequencies of C60 and 64 of the 122 fundamentals of C70. Theoretical calculations for C60 are not accurate enough to completely assign the symmetries of the identified fundamentals. We comment on effects of oxygen and laser power on the Raman spectrum of C60.
Hyperfine Interactions | 1997
Francis L. Pratt; Stephen J. Blundell; P.A. Pattenden; W. Hayes; K.H. Chow; Andrew P. Monkman; T. Ishiguro; K. Ishida; K. Nagamine
We report studies of spin dynamics in the conducting polymers polyaniline and polypyrrole using both μ+SR and μ-SR techniques. These measurements reveal characteristic field dependences and cutoff frequencies for the muon spin relaxation which can be related to the spin diffusion process. Clear evidence is seen for increased spin localisation at low temperatures where a crossover occurs from two or three dimensional spin diffusion to a one dimensional diffusion regime.
Solid State Communications | 1994
S.J. Blundell; P.A. Pattenden; R.M. Valladares; Francis L. Pratt; Tadashi Sugano; W. Hayes
We report the observation of a magnetic transition at around 90 mK in the nitronyl nitroxide radical system para-pyridyl nitronyl nitroxide (p-PYNN) in zero applied field using the muon-spin rotation (μSR) technique.
Journal of Physics: Condensed Matter | 1997
Stephen J. Blundell; F. L. Pratt; P.A. Pattenden; M. Kurmoo; K.H. Chow; Seishi Takagi; Th. Jestädt; W. Hayes
We report the first muon-spin relaxation study of an organic spin - Peierls system, the linear-chain compound MEM(TCNQ). Our results show a crossover from a Gaussian relaxation to an exponential relaxation as the temperature is lowered below the spin - Peierls transition. We associate this behaviour with the slowing down of the electronic fluctuations resulting from the opening of a gap in the magnetic excitation spectrum.
Journal of Physics: Condensed Matter | 1996
S.J. Blundell; Tadashi Sugano; P.A. Pattenden; Francis L. Pratt; R.M. Valladares; K.H. Chow; Hidehiro Uekusa; Yuji Ohashi; W. Hayes
We report the results of muon-spin-rotation/relaxation () experiments on two recently discovered nitronyl nitroxides, 1- and 2-naphthyl nitronyl nitroxide (1-NAPNN and 2-NAPNN). These two compounds are chemical isomers but, because of their slightly different molecular shapes, they have quite different crystal packing. A clear magnetic transition in the zero-field muon-spin relaxation is observed in 1-NAPNN below 100 mK while no such transition is seen in 2-NAPNN. These results support the postulate that the crystal structure strongly influences the nature of the magnetic ground states in these materials.
Synthetic Metals | 1995
P.A. Pattenden; R.M. Valladares; F. L. Pratt; S.J. Blundell; A.J. Fisher; W. Hayes; Tadashi Sugano
Abstract Recently, ferromagnetism has been observed in a family of organic molecular crystals based on the nitronyl nitroxide radical group. We report zero-field μSR measurements on compressed powder samples of the organic magnets p -NPNN and 3-QNNN which have been used to directly probe the temperature dependence of the spontaneous field and the relaxation rate in each system. In p -NPNN, we observe a temperature dependence of the spontaneous field which is very similar to that seen in an aligned single crystal experiment and yield the same Curie temperature ( T C = 670 mK). However, the oscillations in the measured signal are very strongly damped, particularly so just below the transition temperature. In 3-QNNN, the oscillations indicate a lower spontaneous field and a smaller Curie temperature ( T C = 210 mK).
Hyperfine Interactions | 1997
Stephen J. Blundell; P.A. Pattenden; F. L. Pratt; K.H. Chow; W. Hayes; Tadashi Sugano
Ferromagnetism has been observed in a family of organic molecular crystals based on the nitronyl nitroxide radical. We present the results of μSR 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. μSR can be used to study these ground states and thus help to relate the observed magnetic properties to the crystal structure of each material.
Synthetic Metals | 1995
Francis L. Pratt; R.M. Valladares; P.A. Pattenden; S.J. Blundell; W. Hayes; Andrew P. Monkman; K. Nagamine
Abstract Muon techniques have been used to study the spin excitations in polyaniline. The relaxation rate provides information about the spin dynamics: ID spin diffusion is observed at low temperature in non-metallic materials with a crossover to 2 or 3D behaviour at higher temperature. In the metallic polyaniline, in contrast to the undoped cases, the relaxation is rapidly quenched by field at all temperatures. Static and dynamic terms in the relaxation can be separated. The dynamic term shows a high field cutoff which occurs around 25 G at 20 K. This relaxation behaviour indicates a broad spectrum of spin fluctuations concentrated at frequencies in the region below 0.3 MHz. This is a frequency region that is somewhat lower than previously studied by other probes of spin dynamics.
Synthetic Metals | 1997
Francis L. Pratt; K. Ishida; K. Nagamine; P.A. Pattenden; Th. Jestädt; K.H. Chow; S.J. Blundell; W. Hayes; Andrew P. Monkman
The muon is a valuable probe of spin excitations in polymers, as the muon implantation process itself generates a test 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.
Physica B-condensed Matter | 1996
S.J. Blundell; S.R. Brown; K.H. Chow; D. W. Cooke; S. F. J. Cox; S.P. Cottrell; Claude Godart; L. C. Gupta; Z. Hossain; R.L. Lichti; A. Morrobel-Sosa; Chandan Mazumdar; R. Nagarajan; P.A. Pattenden; F. L. Pratt; J. L. Smith
Abstract Implanted muon spectroscopy shows that magnetic order coexists with superconductivity in TmNi2B2C. The muon response indicates that large amplitude fluctuations of the internal field are superimposed on a relatively small static component. The static field exhibits an unusual temperature dependence which shows no interruption at the superconducting transition and may represent evolution of a staggered or spiral arrangement of Tm moments. The dynamic component changes its spectral density at the superconducting transition and the question arises as to whether this is associated with Ni moment formation and fluctuation. In LuNi2B2C, where the rare earth ion is nonmagnetic, no signature of static order is seen. An intriguing change in the muon response does occur below about 4 K in this material; this seems suggestive of Ni moment fluctuation, although the evidence is not entirely conclusive.