BaCo 2Si 2O 7: A new one-dimensional antiferromagnet based on chains of oxide bridged CoO 4 tetrahedra

Abstract

The new compound BaCo 2Si 2O 7 was obtained by heating the mixture BaCO 3, CoCO 3 and SiO 2 to 1300°C for 48 h. The material was characterized by single-crystal X-ray diffraction and magnetic susceptibility measurements. Each cobalt ion is surrounded by four oxygen atoms arranged in a distorted tetrahedral shape. These tetrahedral are linked into chains through the sharing of one of the oxygen atoms. The CoO 4 chains are cross-linked by bridging Si 2O 7 groups. The barium ions occupy channels that run parallel to the crystallographic c-axis. The effective magnetic moment, μ eff = 4.70 B.M., at 25°C is consistent with Co 2+ in a tetrahedral environment having three unpaired electrons. Anti-ferromagnetic coupling of the electrons occurs between the nearest neighbour cobalt ions, as indicated by the sign of the Weiss constant, θ p = −46 K, and by the presence of a broad maximum in the susceptibility curve. At 26 K it undergoes a three-dimensional magnetic transition into a field-induced weak ferromagnet that is characteristic of a one-dimensional metamagnet.