Field-Induced Spin-Structural Transition and Giant Magnetostriction in Ising Chain α-CoV2O6

We have investigated the temperature and magnetic field dependence of magnetization, specific heat (C-p), and relative sample length change (Delta L/L-0) for understanding the field-induced spin-structural change in quasi-one-dimensional spin chain alpha-CoV2O6 which undergoes antiferromagnetic (AFM) transition below T-N = 15 K. Analysis of C-p(T) shows that an effective S = 1/2 Ising state is realized below 20 K, though the magnetic fluctuations persist well above T-N. C-p and the coefficient of linear thermal expansion (alpha) exhibit strong H dependence in the AFM state. We also observe a huge positive magnetostriction [Delta L(H)/L-0] below 20 K which does not show any tendency of saturation up to 9 T. With increasing field, a sharp and symmetric peak emerges below T-N in both C-p(T) and alpha(T) due to field-induced first-order ferrimagnetic/ ferromagnetic-paramagnetic transitions. The large value of magnetostriction below T-N suggests strong spin lattice, coupling in alpha-CoV2O6.