Professor Stephen Blundell

Abstract:

We present the results of recent muon-spin rotation (muSR) experiments on a variety of novel 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. The spin-crossover phenomenon has been studied in Fe(PM-PEA)(2)(NCS)(2), which shows Gaussian and root-exponential muon relaxation in the high-spin and low-spin phases, respectively. Dy spin fluctuations have been studied with muSR in the ferrimagnetic chain Dy(hfac)(3)(NITEt). 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:

Peaks in the interlayer magnetoresistance of the layered superconductor kappa-(BEDT-TTF)(2)Cu(NCS)(2) are observed in the presence of an exactly in-plane magnetic field. The existence of these resistance peaks implies the presence of a three-dimensional Fermi surface extending in the interlayer region. Analysis of the width of the peaks yields a value for the interlayer transfer integral. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract:

Zero field (ZF) muon spin relaxation measurements on the organic metal kappa-BETS2FeCl4 clearly show the formation of an antiferromagnetically ordered state below T-N = 0.45 K. The magnetic order remains unperturbed on cooling through the superconducting transition T-c similar to0.17 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. (C) 2002 Elsevier Science B.V. All rights reserved.

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.