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The magnetic susceptibility and magnetization of high quality single crystal β-TeVO 4 are reported. We show that this compound, made of weakly coupled infinite chains of VO 5 pyramids sharing corners, behaves as a S = ½ one-dimensional Heisenberg antiferromagnet. I. INTRODUCTIONVanadium oxides with the V 4+ ions (S = ½) are excellent model systems for one-dimensional spin-½ quantum magnets. Most studies have been focused on two classes of vanadium oxide chains with edge-and corner-shared VO n polyhedra (VO 5 square pyramids or VO 6 octahedra). Compounds in which adjacent building blocks share their edges are good realizations of the one-dimensional (1D) Heisenberg Hamiltonian.1 In compounds built up of the corner-sharing topology, the nearest-neighbor (NN) exchange coupling may be more then an order of magnitude smaller 2, 3 and an important role of the next-nearest neighbor (NNN) interactions take place. The interplay between frustration and quantum spin fluctuations results in a rich phase diagram with commensurate/incommensurate phases and unusual magnetic properties of these materials.Recently, α-TeVO 4 with the zigzag chains formed by distorted VO 6 octahedra sharing edges have been discovered as a quasi-one-dimensional spin-½ Heisenberg system with alternating NN ferromagnetic (FM) interactions and NNN antiferromagnetic (AF) interaction. 4 As it was known 5 , the compound TeVO 4 can be prepared in two different crystalline forms with a reversible polymorphic transformation at 650°C (α↔β). In contrast to α-phase, β-TeVO 4 has a significant difference in its structure: the zigzag chains are formed by distorted VO 5 pyramids sharing their corners. Thus, the corner-sharing of VO 5 pyramids can lead to the considerable reducing of a scale of the existing exchange interactions in the 1D spin system.In this paper, we report on the single crystal magnetic properties of a quasi-one-dimensional spin-½ chain system, β-TeVO 4 . Though this compound phase has been known for a long time 5 , to our knowledge, its magnetic properties on powdered or single crystal samples were hitherto not reported at all. We discuss that the actual topology of magnetic couplings for such system might be indeed more complex than originally envisioned.

The effect of a magnetic field on the magnetic susceptibility χ(T) and the temperature of the three magnetic phase transitions in single-crystal β-TeVO4 is studied at low temperatures. The H-T phase diagram is obtained for H||b and H ⊥ b. A tricritical point with coordinates H* = 3.2 ± 0.1 T and T* = 3.0 ± 0.1 K is found for H||b.