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Abstract:

A new layered iron arsenide NaFeAs isostructural with the superconducting lithium analogue displays evidence for the coexistence of superconductivity and magnetic ordering.

Abstract:

The probability distribution of local magnetic field values experienced by implanted muons, given no prior information on the muon site, is calculated for various arrangements of magnetic dipoles commonly found in magnetic materials. Such distributions are useful for interpreting μSR data on complex magnetic systems such as molecular magnets where there are many possible muon sites. © 2009 Elsevier B.V. All rights reserved.

Abstract:

A new μ SR spectrometer (HiFi) is being constructed at the ISIS pulsed muon source. The spectrometer is intended for measurements in longitudinal magnetic fields up to 5 T. Here we discuss various aspects of the design and future operation of the HiFi spectrometer. Detailed analysis of the detector design is presented, and results from tests on detector prototypes are compared to simulations. Potential applications of this spectrometer in the fields of condensed matter and chemistry are also discussed. © 2008 Elsevier B.V. All rights reserved.

Abstract:

Systematic studies of magnetic critical exponents in local moment molecular magnets can be made by combining three different types of μ SR measurement; zero-field precession, longitudinal relaxation and the frequency shift in transverse field. Systems have been studied with 1D, 2D and 3D structures, having both simple and non-collinear magnetic interactions and the measurements have included investigation of the effect of chirality on the critical spin fluctuations. In the case of the model S = frac(1, 2) Heisenberg antiferromagnetic 1D chain Heisenberg antiferromagnetic quantum critical fluctuations suppress magnetic ordering and TCNQ radical ion salts can provide some excellent examples of this model. In particular, DEOCC-TCNQF4 behaves as a nearly ideal case with no ordering seen down to 20 mK even though the intrachain exchange interaction is 110 K. In contrast the DMTzNC-TCNQ compound orders at 1.5 K, but still shows evidence for significant residual quantum fluctuations in its ordered state in the form of a large suppression of the magnitude of the ordered part of the magnetic moment. From analysis of the characteristic field dependent muon relaxation behaviour as a function of temperature above the transition, the nature of the spin fluctuations is found to change as the transition is approached, suggesting a crossover either to 2D diffusion or to 1D ballistic motion. © 2008 Elsevier B.V. All rights reserved.

Abstract:

X-ray powder diffraction and magnetic susceptibility measurements show that Ag(pyz)(2)(S(2)O(8)) consists of 2D square nets of Ag(2+) ions resulting from the corner-sharing of axially elongated AgN(4)O(2) octahedra and exhibits characteristic 2D antiferromagnetism. Nevertheless, mu(+)SR measurements indicate that Ag(pyz)(2)(S(2)O(8)) undergoes 3D magnetic ordering below 7.8(3) K.