In the strontium iron-cobalt arsenides SrFe2-xCoxAs2 (0.2 < or = x < or = 0.4) superconductivity with T_{c} up to 20 K is observed in magnetic susceptibility, electrical resistivity, and specific heat data. This first observation of bulk superconductivity induced by electron doping in this family of compounds-despite strong disorder in the Fe-As layer-favors an itinerant electronic theory in contrast to the strongly correlated cuprates and renders a p- or d-wave pairing unlikely. The magnetic ordering present in SrFe2As2 is rapidly suppressed by substitution of Fe by Co. Density functional theory calculations show that this is due to a rigid downshift of the Fe-3d_{x;{2}-y;{2}}-related band edge in the density of states.

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New germanium-platinum compounds with the filled-skutterudite crystal structure were synthesized. The crystal structure and composition were investigated by x-ray diffraction and microprobe analysis. Magnetic susceptibility, specific heat, and electrical resistivity measurements evidence superconductivity in LaPt4Ge12 and PrPt4Ge12 below 8.3 K. The parameters of the normal and superconducting states were established. Strong coupling and a crystal electric field singlet ground state is found for the Pr compound. Electronic structure calculations show a large density of states at the Fermi level. Similar behavior with lower Tc was observed for SrPt4Ge12 and BaPt4Ge12.

Single crystalline Sn 2 Co 3 S 2 with the shandite-type structure was investigated by magnetization, magnetoresistance, Hall effect, and heat capacity measurements and by 119 Sn Mößbauer spectroscopy. Sn 2 Co 3 S 2 orders ferromagnetically at 172 K with an easy-axis magnetization of ≈1 μ B along the hexagonal c axis. The half-metallic ferromagnetic state is investigated by detailed band-structure calculations by density functional theory (DFT) methods. The magnetoresistance and the Hall effect as well as the DFT results show that ferromagnetic Sn 2 Co 3 S 2 is a compensated metal. The 119 Sn Mößbauer spectroscopic data confirm these findings. Large transferred hyperfine fields B hf up to 34.2 T are observed.