Phase diagram and magnetic structures of the Co-bearing dugganites Pb ₃TeCo₃A₂O₁₄ (A = V, P)

Exhibiting rich magnetic behaviour and potentially multiferroic properties, the dugganites, a Te⁶⁺ containing subgroup of the langasite series, are an attractive family of compounds for future study. It was recently shown that Pb-bearing members of the dugganite series undergo distortions away from the P321 symmetry that is characteristic of the langasites. Here, we detail the consequences these distortions have on the magnetism exhibited by Pb ₃TeCo₃V₂O₁₄ and Pb ₃TeCo₃P₂O₁₄, solving the magnetic structures of both compounds with respect to a new supercell. Using neutron scattering and magnetic susceptibility measurements, we show that small applied magnetic fields can seriously perturb the delicate magnetic states in both of these systems. This is further demonstrated by presenting how doping P ⁵⁺ onto the nonmagnetic V⁵⁺ site completely changes the magnetic structure from either of the end series members. Finally, it is shown using inelastic neutron scattering and magnetic susceptibility measurements that Pb₃TeCo₃V₂O₁₄ can be characterized using a model for isosceles trimers, which do not exist in the previously reported P321 subcell.