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We have performed inelastic neutron scattering on a single crystal sample of Sr 14 Cu 24 O 41 to study the spin dynamics of the Cu 2 O 3 spin ladder layers, and CuO 2 chains. Data collected with incident energies of 50 meV, 200 meV, 350 meV and 500 meV are best fitted with a dispersion with a spin gap of 32.5±0.1 meV and a maximum of 193.5±2.4 meV, consistent with a coupling along the ladders, J || = 130 meV and a rung coupling J ⊥ =72 meV. We find that excitations with an energy transfer of approximately 11.5 meV can be described solely in terms of a dimer chain with an antiferromagnetic intra-dimer coupling, J 1 = 11.2 meV, between next-nearest-neighbour Cu ions and a ferromagnetic inter-dimer coupling, J 2 = -1.1 meV. The dimers are separated by two Cu ions providing a periodicity for the dimer chain of five units.

Hole distribution for (Sr,Ca,Y,La)14Cu24O41 ladder compounds studied by x-ray absorption spectroscopy Nücker, N.; Merz, M.; Kuntscher, C.A.; Gerhold, S.; Schuppler, S.; Neudert, R.; Golden, M.S.; Fink, J.; Schild, D.

We report significant intergrain magnetoresistance (IMR) in polycrystalline double perovskites of SrFe1−x(Mo or Re)xO3 at room temperature. Systematics of the temperature dependence of IMR indicates that the observed large room-temperature IMR in SrFe1/2Mo1/2O3 originates from the ferrimagnetic nature of insulating grain boundaries as well as the half-metallicity of this perovskite. Our results indicate that a new avenue for spin-polarized tunneling junctions is to utilize insulating interface layers with ferromagnetic or ferrimagnetic coupling.

We measured thermal conductivity kappa, thermoelectric power S, and electric conductivity sigma of La(5/8-x)Pr(x)Ca(3/8)MnO3, showing an intricate interplay between metallic ferromagnetism (FM) and charge ordering (CO) instability. The change of kappa, S, and sigma with temperature (T) and x agrees well with the effective medium theories for binary metal-insulator mixtures. This agreement clearly demonstrates that with the variation of T as well as x, the relative volumes of FM and CO phases drastically change and percolative metal-insulator transition occurs in the mixture of FM and CO domains.

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