Large magnetic anisotropy of a decorated spin-chain system K2Co3(MoO4)3(OH)2

The magnetic structure of K₂Co₃(MoO₄)₃(OH)₂ is studied in detail. The material has a half-sawtooth one-dimensional (1-D) structure containing two unique Co²⁺ ions, one in the chain backbone and one on the apex of the sawtooth creating a series of isosceles triangles along the b-axis. These triangles can be a source of magnetic frustration. The ability to grow large single crystals enables detailed magnetic measurements with the crystals oriented in a magnetic field along the respective axes. It has a Curie-Weiss temperature θ_CW of 5.3(2) K with an effective magnetic moment of 4.8(3)μ_B/Co. The material is highly anisotropic with a sharp antiferromagnetic ordering transition at 7 K with a metamagnetic transition at 2 kOe. Neutron diffraction was used to determine the magnetic structure and revealed a magnetic structure with canted spins along the backbone of the chain while spins along the sawtooth caps maintained a colinear orientation, arranging antiferromagnetically relative to the backbone spins. The parallel chains arrange antiferromagnetically relative to each other along the c-axis and ferromagnetically along the a-axis.