Thermodynamics of the bilinear-biquadratic spin-one Heisenberg chain

The magnetic susceptibility and specific heat of the one-dimensional S = 1 bilinear-biquadratic Heisenberg model are calculated using the transfer mat rix renormalization group. By comparing the results with the experimental d ata of LiVGe2O6 measured by Millet ct al. [Phys. Rev. Lett. 83, 4176 (1999) ], we find that the susceptibility data of this material, after subtracting the impurity contribution, can be quantitatively explained with this model . The biquadratic exchange interaction in this material is found to be ferr omagnetic, i.e., with a positive coupling constant.