Crystal and Magnetic Structures of Selected Strongly Correlated Electron Systems

Serena Margadonna

Chemistry Department, University of Cambridge, Lensfield Road, CB2 1EW Cambridge, UK

Recent advances in diffraction instrumentation at the ILL (construction of Super D2b) have allowed the collection of high-quality data even on small samples which adopt complex disordered structures. In this presentation, I will discuss some of our recent structural and magnetic work on strongly correlated electron systems, which include: (i) the structural and magnetic characterisation of switchable systems exhibiting multistability, e.g. the family of mixed valence transition metal cyanides (Prussian blue analogues), (ii) the structural characterisation of intermediate valence rare-earth systems exhibiting zero- or negative- thermal expansion, driven by electronic instabilities, and (iii) the origin of the anomalous magnetic behaviour of the antiferromagnetic insulators (NH3)K3-xRbxC60 (x = 0-3) where TN first increases with lattice expansion and then swiftly decreases, in sharp contrast to what is expected for simple localised moment models (a smooth decrease in the exchange interaction, J and TN with increasing lattice constant). Complementary information obtained from synchrotron X-ray powder diffraction measurements are utilized throughout.