Neutron diffraction study of the layered compounds MnPSe 3 and FePSe 3

In the insulating compounds MnPSe ₃ (1) and FePSe ₃ (2) the divalent transition metal ions form planar honeycomb lattices. A neutron diffraction study revealed a collinear antiferromagnetic order below T_N = 74 ± 2 K (1) and T_N = 119 ± 1 K (2) with the corresponding wavevectors k = [000] (1) and k = [ {1}/{2} 0 {1}/{2}] (2). In MnPSe ₃ the magnetic moments ( m₀ = 4.74 μ_B) lie within the basal plane and in FePSe ₃ ( m₀ = 4.9 μ_B) they are pointing along the c-axis. The collinear structures are determined by the dominating intralayer interactions between first ( J₁), second ( J₂) and third neighbours ( J₃) which in MnPSe ₃ are all antiferromagnetic whereas in FePSe ₃J₁ is ferromagnetic and J₂ and J₃ are antiferromagnetic.