Abstract

We have investigated crystal structures and magnetic properties of cobalt chalcogenides BaLa₂Co(S_1 − xSe_x)₅ (0.0 ≤ x ≤ 0.4). This system has a tetragonal crystal structure with the space group I4/mcm. The lattice constants a and c increase linearly with Se content x. The temperature dependence of the magnetic susceptibilities of BaLa₂Co(S_1 − xSe_x)₅ shows that the antiferromagnetic transition temperature (63–65 K) increases and the magnetic moment of Co²⁺ decreases with increasing x. Their specific heat shows the decrease of the Debye temperatures with increasing x. The neutron diffraction data collected at 10 K for BaLa₂CoS₅ indicate that the Co²⁺ ions have a collinear antiferromagnetic structure with an ordered moment of 3.56 μ_B. The magnetic moments lie in a parallel direction with the c-axis.