Superconducting and normal-state properties of the layered boride OsB2

OsB2 crystallizes in an orthorhombic structure (Pmmn) which contains alternate boron and osmium layers stacked along the c axis. The boron layers consist of puckered hexagons as opposed to the flat graphite-like boron layers in MgB2. OsB2 is reported to become superconducting below 2.1 K. We report results of the dynamic and static magnetic susceptibilities, electrical resistivity, Hall effect, heat capacity, and penetration depth measurements on arc-melted polycrystalline samples of OsB2 to characterize its superconducting and normal-state properties. These measurements confirmed that OsB2 becomes a bulk superconductor below T-c = 2.1 K. Our results indicate that OsB2 is a moderate-coupling type-II superconductor with an electron-phonon coupling constant lambda(ep) approximate to 0.4-0.5, a small Ginzburg-Landau parameter kappa similar to 1-2, and an upper critical magnetic field H-c2 (0.5K) similar to 420 Oe for an unannealed sample and H-c2(1 K) similar to 330 Oe for an annealed sample. The temperature dependence of the superfluid density n(s)(T) for the unannealed sample is consistent with an s-wave superconductor with a slightly enhanced zero temperature gap Delta (0)= 1.9k(B)T(c) and a zero temperature London penetration depth lambda(0)=0.38(2) mu m. The n(s)(T) data for the annealed sample show deviations from the predictions of the single-band s-wave BCS model. The magnetic, transport, and thermal properties in the normal state of isostructural and isoelectronic RuB2, which is reported to become superconducting below 1.6 K, are also reported.