Magnetic susceptibility and electrical conductivity of transition-metal platinum oxides. Evidence for one-dimensional electronic interactions

Bulk magnetic susceptibility measurements have been made on the orthorhombic compounds CoPt₃O₆, MnPt₃O₆, and NiPt₃O₆, and the structurally related cubic phase Co_0.37Na_0.14Pt₃O₄, in the temperature range 300-4 K. These compounds, which are rather unusual in that they contain first-row transition metals in eight coordination, are all paramagnetic above 25 K and show Curie-Weiss behavior with effective magnetic moments μ_eff(Co) = 4.8 ± 0.2μ_B,μ_eff(Mn) = 5.8 ± 0.1 μ_B, μ_eff(Ni) = 3.9 ± 0.2 μ_B, and μ_eff(Co) = 4.2 ± 0.5 μ_B, respectively. The inverse susceptibilities of CoPt₃O₆ and MnPt₃O₆ exhibit deviations from Curie-Weiss behavior below 25 K, and a minimum is observed for CoPt₃O₆ at about 8K. Single-crystal electrical conductivity measurements along the c-axis (σ_∥) in CoPt₃O₆ and MnPt₃O₆ show these materials to be semiconducting, but with relatively high conductivities and low activation energies σ_∥ (294 K) = 40 Ω^-1-cm^-1 and E_a = 0.07 eV for CoPt₃O₆ and σ_∥ (303 K) = 111Ω^-1cm^-1 and E_a = 0.02 eV for CoPt₃O₆. The results for CoPt₃O₆. MnPt₃O₆, and NiPt₃O₆are discussed in terms of their anisotropic structures, which favor magnetic coupling in one-dimension along linear arrays of eight-coordinated paramagnetic ions and one-dimensional electrical conduction along columnar stacks of planar PtO₄ groups containing partially oxidized linear chains of platinum. One-dimensional electronic interactions in MPt₃O₆ compounds are suggested by metal-metal distances along the c-axis of 3̃.1 A for both the platinum and the 3d transition metal ions, compared to a distance of 6.1 A between the chains in the perpendicular plane. These materials and their electronic properties are compared with systems with well characterized examples of one-dimensional magnetic coupling and electrical conductivity.