Professor Paolo G. Radaelli OSI

Abstract:

The phase-diagram of Ca2-x.SrxRuO4 has been studied by several diffraction techniques as function of concentration, temperature, pressure and magnetic field. The substitution of Sr through the smaller Ca induces a series of structural phase transitions with a strong impact on the physical properties. The spin triplet superconductor Sr 2RuO4 exhibits an undistorted crystal structure, and the Mott-insulator Ca2RuO4 strong structural distortions. For intermediate structural distortions samples stay metallic but with outstanding properties. Throughout the phase diagram we find a close coupling between the crystal structure on one side and magnetic and electronic behavior on the other side. © 2005 Materials Research Society.

Abstract:

We have used electron diffraction and neutron powder diffraction to elucidate the structural properties of superconducting NaxCoO 2•yD2O over a wide compositional range. Our measurements show that superconducting samples exhibit a number of supercells ranging from to , but the predominant modulation, observed also in the neutron data, is a double hexagonal cell with dimensions 2a × 2a × c. Rietveld analysis reveals that D2O is inserted between CoO 2 sheets to form a layered network of NaO6 triangular prisms. Our model removes the need to invoke a 5 K superconducting point compound and suggests that a solid solution of Na is possible within a relatively constant amount of water y. © IOP Publishing Ltd.

Abstract:

High-resolution x-ray and neutron powder-diffraction measurements were performed on polycrystalline VOMoO4. Below ≃ 40K the system orders in a simple Néel antiferromagnetic state (propagation vector k =0), indicating a dominant role of the nearest-neighbor interactions. The order is three dimensional but the reduced saturated magnetic moment m of 0.41 (1) μ V4+ at 2K indicates strongly two-dimensional character and enhanced quantum fluctuations. On cooling, there is no evidence of a reduction of the crystal symmetry. However, neutron diffraction indicates an anomalous evolution of the lattice parameters, which can be related to the onset of magnetic correlations. © 2005 The American Physical Society.