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Magnetic properties of the triclinic copper vanadate ␣-CuV 2 O 6 with linear chains of edge-sharing CuO 6 octahedra were studied by magnetic susceptibility and electron-spin-resonance measurements. The broad maximum of a magnetic susceptibility at T M ϭ44 K corresponding to the intrachain exchange interaction Jϭ34 K indicates one-dimensional short-range magnetic ordering within the chains. Three-dimensional long-range antiferromagnetic ordering takes place at T N ϭ24 K, suggesting a rather large value for the interchain exchange interaction J Ќ ϳ16.5 K. The energy gap found in the antiferromagnetic resonance spectrum 76 GHz agrees with the spin-flop magnetic-field value of about 2.7 T. ͓S0163-1829͑99͒05825-7͔The copper-and vanadium-based complex oxides are frequently found among those inorganic compounds which exhibit a low-dimensional magnetic behavior at lowering temperature. Besides other spin-chain and spin-ladder compounds this behavior was observed recently in CuM 2 O 6 (M ϭSb, Nb͒ compounds. While being of the same chemical formula these compounds possess different crystal structures and therefore different albeit quasi-one-dimensional arrangements of magnetic ions.In the monoclinic copper antimonate CuSb 2 O 6 the main building blocks are constituted by edge and corner sharing CuO 6 and SbO 6 octahedra. The magnetic Cu 2ϩ ions forming square lattices in the a-b plane are separated from each other by two sheets of nonmagnetic Sb 5ϩ ions along the c axis. The dominant antiferromagnetic interaction occurs through a linear Cu-O-O-Cu linkage which connects one set of two next-nearest-neighbor Cu 2ϩ ions. The interaction with other two next-nearest-neighbor Cu 2ϩ ions is frustrated, providing a dominance of quasi-one-dimensional in-plane interaction. The CuSb 2 O 6 exhibits a broad maximum of magnetic susceptibility at T M ϭ60 K and the transition to antiferromagnetic state at T N ϭ8.5 K. 1 The copper niobate was investigated in both monoclinic ␣-CuNb 2 O 6 and orthorhombic ␤-CuNb 2 O 6 polymorphs. Both structures contain zigzag chains of edge-sharing CuO 6 octahedra, separated by chains of edge-sharing NbO 6 octahedra forming washboardlike planes by the linkage of corner oxygens. The ground state of the ␣-CuNb 2 O 6 is separated by a spin gap from the excited states due to the alternating exchange coupling between the Cu 2ϩ spins within the quasione-dimensional chains. 2 The ␤-CuNb 2 O 6 exhibits a broad maximum of magnetic susceptibility at T M ϭ20 K followed by antiferromagnetic transition at T N ϭ7.5 K. 3

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