RESUMEN
We combine infrared and Raman spectroscopies to investigate finite length scale effects in CuGeO3 nanorods. The infrared-active phonons display remarkably strong size dependence whereas the Raman-active features are, by comparison, nearly rigid. A splitting analysis of the Davydov pairs reveals complex changes in chemical bonding with rod length and temperature. Near the spin-Peierls transition, stronger intralayer bonding in the smallest rods indicates a more rigid lattice which helps to suppress the spin-Peierls transition. Taken together, these findings advance the understanding of size effects and collective phase transitions in low-dimensional oxides.
RESUMEN
dc Magnetic susceptibility measurements and the torque magnetometry were used to experimentally probe the symmetry of the antiferromagnetically (AFM) ordered state of Bi(2)CuO(4). A phenomenological approach to the anisotropy energy is used to model the angular dependence of torque for easy axis and easy plane anisotropy. Comparison of these results with the experimentally obtained curves leads to the conclusion that the antiferromagnetically ordered state in Bi(2)CuO(4) has an easy plane anisotropy with the c plane as an easy plane. The estimated value of the critical field for the spin-flop in the easy plane is H(c)≈15-20 kOe giving the easy plane anisotropy energy constant K(22)≈27-47×10(3) erg mol(-1). The resulting antiferromagnetic structure contains two equally populated mutually perpendicular AFM domains in zero magnetic field.
