Melzi R, Carretta P, Lascialfari A, Mambrini M, Troyer M, Millet P, Mila F
Dipartimento di Fisica "A. Volta," Unita INFM di Pavia, 27100 Pavia, Italy.
Phys Rev Lett. 2000 Aug 7;85(6):1318-21. doi: 10.1103/PhysRevLett.85.1318.
NMR and magnetization measurements in Li2VOSiO4 and Li2VOGeO4 are reported. The analysis of the susceptibility shows that both compounds are two-dimensional S = 1/2 Heisenberg antiferromagnets on a square lattice with a sizable frustration induced by the competition between the superexchange couplings J1 along the sides of the square and J2 along the diagonal. Li2VOSiO4 undergoes a low-temperature phase transition to a collinear order, as theoretically predicted for J2/J1>0.5. Just above the magnetic transition the degeneracy between the two collinear ground states is lifted by the onset of a structural distortion.
