Ferromagnetism and Spin Liquid Behavior in [Mo₃]¹¹⁺ Molecular Magnets

Molecular magnets based on [Mo₃]¹¹⁺ units with one unpaired electron per trimer have attracted recent interest due to the identification of quantum spin liquid candidacy in the family member LiZn₂Mo₃O₈. Here, we present comprehensive measurements on polycrystalline samples of the three related systems ZnScMo₃O₈, MgScMo₃O₈, and Na₃Sc₂Mo₅O₁₆ with the same Mo₃O₁₃ magnetic building blocks. The crystal structures are characterized with powder x-ray diffraction and the magnetic ground states are determined by performing AC and DC susceptibility, specific heat, neutron powder diffraction, and μSR measurements. Our work indicates that ZnScMo₃O₈ and MgScMo₃O₈ are weak ferromagnets, with zero field ordering temperatures of T_C ~ 6 K and T_C<1.5 K respectively. On the other hand, Na₃Sc₂Mo₅O₁₆ hosts a dynamical magnetic ground state and therefore is a candidate for quantum spin liquid behavior. By comparing the present results to past work on the same family of materials, we construct a universal phase diagram for this family of materials which suggests that their magnetic ground states are very sensitive to subtle changes in the nearest-neighbor Mo-Mo distance.