Muons and magnets

Abstract:

Zero field (ZF) muon spin relaxation measurements on the organic metal κ-BETS2FeCl4 clearly show the formation of an antiferromagnetically ordered state below TN = 0.45 K. The magnetic order remains unperturbed on cooling through the superconducting transition Tc ∼0.17 K, providing unambiguous evidence for the coexistence of antiferromagnetic order and superconductivity in this system. Detailed studies of the internal field distribution show contrasting behavior for different muon sites and provide experimental evidence for an ordered spin structure in the BETS layers in addition to that taking place in the Fe layers. © 2002 Elsevier Science B.V. All rights reserved.

Abstract:

Angle-dependent muon spin rotation measurements have been made on the organic superconductor κ-(BEDT-TTF)2Cu(SCN)2. Oscillations are observed in the width of the internal field distribution, which are periodic in the perpendicular component of the applied magnetic field, Bz = B cos θ, with a uniform period over a range of angles and fields. These oscillations are superimposed on the standard cos θ scaling expected for the width in a highly anisotropic superconductor. The oscillation period is of order 2 mT and the amplitude is particularly strong at fields comparable with the period. The origin of this novel phenomenon is discussed in terms of the low field instabilities of tilted vortices in this highly anisotropic superconductor. © 2002 Elsevier Science B.V. All rights reserved.

Abstract:

μSR 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 μSR to study the muon states and muon mobility in the polymers polyethylene and polytetrafluoroethylene, where coherent FμF 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. © 2002 Elsevier Science B.V. All rights reserved.

Abstract:

Dilution on the B-site with Ir or Rh can lead to the enhancement of ferromagnetic couplings in layered manganites. We report a muSR study of the spin dynamics of the layered manganites La0.25Sr1.75MnpIr1-pO4 (p = 0.5, 0.75) as a function of the dilution. We have characterized the static magnetic behavior using SQUID magnetic measurements and used muon spin relaxation spectroscopy to provide evidence for short-range ferromagnetic correlations. Furthermore, the effect of dilution on the critical dynamics in this two-dimensional spin system is reported and related to the dynamics above and below the critical percolation threshold. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract:

Angle-dependent muon spin rotation measurements have been made on the organic superconductor kappa-(BEDT-TTF)(2)Cu(SCN)(2). Oscillations are observed in the width of the internal field distribution, which are periodic in the perpendicular component of the applied magnetic field, B-z = B cos theta, with a uniform period over a range of angles and fields. These oscillations are superimposed on the standard cos theta scaling expected for the width in a highly anisotropic superconductor. The oscillation period is of order 2 mT and the amplitude is particularly strong at fields comparable with the period. The origin of this novel phenomenon is discussed in terms of the low field instabilities of tilted vortices in this highly anisotropic superconductor. (C) 2002 Elsevier Science B.V. All rights reserved.