Determination of the exchange energies in Li2VOSiO4from a high-temperature series analysis of the square-lattice J1-J2 Heisenberg model

We present a high-temperature expansion (HTE) of the magnetic susceptibility and specific heat data of Melzi et al. on Li 2 VOSiO 4 [Phys. Rev. B 64, 024409 (2001)]. The data are very well reproduced by the J 1 -J 2 Heisenberg model on the square lattice with exchange energies J 1 =1.25′0.5 K and J 2 =5.95′0.2 K. The maximum of the specific heat C m a x υ (T m a x ) is obtained as a function of J 2 /J 1 from an improved method based on HTE.