Physical properties of the novel ruthenate La_(3.5)Ru_4O_(13): Possible mixed valence of Ru ions

摘要

Structural, magnetization, heat capacity, and electrical resistivity measurements have been carried out on a new ruthenate compound La_(3.5)Ru_4O_(13). This compound forms in the orthorhombic structure (Pmmm space group, #47). The coexistence of the triple-layered perovskite-type planes [quasi-two-dimensional (2D) structure] and the rutilelike slabs [one-dimensional (1D) structure] leads to interesting magnetic and electronic properties in this compound. The relatively short Ru-O bond distances or stronger 4d-2p hybridization of rutilelike slabs suggest an electronic delocalization feature along the slab axis (b-axis). In the high-temperature region, a Curie-Weiss behavior of the magnetic susceptibility is observed with an effective magnetic moment μ_(eff) = (2.44 ± 0.02) μ_B per Ru ion and a paramagnetic Curie temperature θ_p=-198 ± 2 K. The magnetic susceptibility of this compound shows a peak at T～ 47 K typical of an antiferromagnetic (AFM) order which is confirmed by heat capacity measurements. This AFM order can be associated with the AFM coupling of Ru ions of the quasi-2D layers. The electronic specific heat coefficient y is found to be 12 mJ/mol_(Ru)K_2, suggesting moderate carrier correlations. Resistivity and magnetic data suggest that the quasi-2D substructure shows semiconducting behavior, while a metallic behavior is expected for the 1D slabs.