Professor Stephen Blundell

Abstract:

The two-dimensional antiferromagnet [Cu(HF2)2(pyz)] n (pyz=pyrazine) has a rectangular lattice (see picture) displaying two types of FHF- bridging modes. The spin exchange through Cu-(FHF)2-Cu is about 90% stronger than through Cu-pyz-Cu, and the 1,1-coordinated FHF-, which is close in nature to F - ⋯ HF, is largely responsible for the exchange. C black, Cu red, F green, H cyan. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Abstract:

A muon-spin relaxation (μ+SR) investigation is presented for the molecular superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br. Evidence is found for low-temperature phase separation throughout the bulk of the material, with only a fraction of the sample showing a superconducting signal, even for slow cooling. Rapid cooling reduces the superconducting fraction still further. For the superconducting phase, the in-plane penetration depth is measured to be λ||=0.47(1)μm, and evidence is seen for a vortex decoupling transition in applied fields above 40 mT. The magnetic fluctuations in the normal state produce a precipitous drop in relaxation rate above 100 K, and we discuss the possible causes for the unusual relaxation that we observe for T>Tc. © 2011 American Physical Society.