Magnetic crossover and complex excitation spectrum of the   ferromagnetic/antiferromagnetic spin-1/2 chain system alpha-TeVO4
  We report magnetic susceptibility, specific heat, and Raman scattering investigations of alpha-TeVO4 containing V-O edge-sharing chains. These chains promote a system of ferromagnetic/antiferromagnetic spin-1/2 Heisenberg alternating exchange chains with pronounced spin frustration. The magnetic susceptibility and Raman scattering evidence a crossover at T* = 85 K with different slopes of the reciprocal susceptibility and a magnetic phase transition into a long-range-ordered state at Tc = 16 K. From Raman scattering data a strong mutual coupling between lattice and magnetic degrees of freedom is deduced. A comparison to model calculations and prior Raman scattering on other chain systems yield a plausible interpretation of the microscopic mechanism for the crossover behavior. 
V. Gnezdilov, P. Lemmens, A. A. Zvyagin, V. O. Cheranovskii, K.   Lamonova, Yu. G. Pashkevich, R. K. Kremer, and H. Berger