Muons and magnets

Abstract:

We report the results of muon-spin-rotation/relaxation (μ+SR) 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.

Abstract:

Millimetre wave magnetotransmission measurements are used to provide the first clear evidence for magnetic defects in CeNiSn. At least two defect configurations are observed, both probably involving Ce3+ ions.

Abstract:

We review recent studies of charge-transfer salts of the ion bis(ethylenedithio)tetrathiafulvalene which exhibit spin-density wave ground states, concentrating on techniques involving high magnetic fields and experiments carried out by the oxford group and coworkers.

Abstract:

The structure of the wave of the phase transformation in the deterministic discrete model of non-equilibrium phase transitions is investigated. In this model each of the cells forming a two-dimensional lattice can be in one of three states: stable, metastable or excited. The transition into the stable state is allowed only through an intermediate excited state. The change of the phase state of each cell is initiated by the variation of a continuous parameter, the 'temperature', taking into account the energy exchange between cells, the phase stability regions and local rules in the neighbourhood of the cell. Taking the square and hexagonal lattices as examples, it is shown that this model possesses the following fundamental property: when the lifetime of the excited states is increased beyond a certain threshold, an abrupt change of the dynamics of the phase transition occurs. The wavefront then acquires a beam-like or fractal-like structure and, in the latter case, the system of cells has a quasicontinuous frequency spectrum of white or coloured noise. The application of this model to the description of non-equilibrium (explosive) crystallization in amorphous metals and semiconductors is discussed.