Successive short- and long-range magnetic ordering in rosiaite-type CoGeTeO6 prepared by ion-exchange reaction

Abstract

The missing member of the rosiaite family, CoGeTeO₆, was synthesized by mild ion-exchange reactions and characterized by magnetization M and specific heat C_p measurements. It exhibits a successive short- and long-range magnetic ordering at T_short-range ≈ 45 K and T_N = 15 K, respectively. Based on these measurements, the magnetic H–T phase diagram was established, showing two antiferromagnetic phases separated by a spin-flop transition. The reason why the pronounced short-range correlation occurs at a temperature nearly three times higher than T_N was found by evaluating the Co–O⋯O–Co exchange interactions using energy-mapping analysis. Although CoGeTeO₆ has a layered structure, its magnetic structure consists of three-dimensional antiferromagnetic lattices made up of rhombic boxes of Co²⁺ ions. The experimental data obtained at high temperatures agree well with the computational results by treating the Co²⁺ ions of CoGeTeO₆ as S = 3/2 ions, but the heat capacity and magnetization data were obtained at low temperatures by treating the Co²⁺ ion as a J_eff = 1/2 ion.