Anomalous electrical and magnetic properties of a new quasi-low-dimensional mixed-valent molybdenum-cluster compound

Large plate-like single crystals of La₅Mo₄O₁₆ were prepared by electrolyzing molten mixtures of La₂O₃, MoO₃ and Na₂MoO₄. The temperature dependence of electrical resistivity in the ab plane and parallel to the c-axis of the single crystal shows semiconducting behavior in the temperature range 180-300 K and a sharp upturn in the resistivity below ∼180 K. The temperature variation of the susceptibility in the temperature range 200-300 K follows Curie-Weiss behavior with an observed moment ∼1.66 B.M. corresponding to one localized electron per formula unit. The magnetization study on a batch of randomly oriented single crystals showed a sharp decrease in the susceptibility at ∼180 K indicative of a long-range antiferromagnetic order. Directional magnetization studies on La₅Mo₄O₁₆ indicated that the magnetic ordering is confined to the ab plane. The anomalous electrical and magnetic properties are discussed in terms of the unique structure of La₅Mo₄O₁₆.