Muons and magnets

Abstract:

Zero field muon spin relaxation measurements have been made on the charge transfer salt (tetrakisdimethylaminoethylene)C-60 [TDAE-C-60]. The effects of high temperature annealing on the dynamics and local magnetic properties of the compound are investigated. With the sample in the ferromagnetic alpha-phase, a signal characteristic of magnetic order is observed below 16 K. The initial asymmetry shows a discontinuity around 200 K, while the relaxation rate shows temperature activated behaviour above around 120 K. Annealing at 383 K is found to destroy the ferromagnetic signal and results in a relaxation rate peaked at 10 K, which may be attributable to the freezing out of a dynamic Jahn-Teller distortion.

Abstract:

Organic molecular FETs provide an experimental framework for studying the band-filling dependent properties of two-dimensional metals. We propose experiments to investigate the band-filling dependent cyclotron resonance and the effect of van Hove singularities. (C) 2002 Elsevier Science B.V. All rights reserved.

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.