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

Abstract

Bulk magnetic susceptibility measurements have been made on the orthorhombic compounds CoPt 3O 6, MnPt 3O 6, and NiPt 3O 6, and the structurally related cubic phase Co 0.37Na 0.14Pt 3O 4, 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 CoPt 3O 6 and MnPt 3O 6 exhibit deviations from Curie-Weiss behavior below 25 K, and a minimum is observed for CoPt 3O 6 at about 8K. Single-crystal electrical conductivity measurements along the c-axis (σ ∥) in CoPt 3O 6 and MnPt 3O 6 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 CoPt 3O 6 and σ ∥ (303 K) = 111Ω −1cm −1 and E a = 0.02 eV for CoPt 3O 6. The results for CoPt 3O 6. MnPt 3O 6, and NiPt 3O 6are 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 PtO 4 groups containing partially oxidized linear chains of platinum. One-dimensional electronic interactions in MPt 3O 6 compounds are suggested by metal-metal distances along the c-axis of 3̃.1 A for both the platinum and the 3 d 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.