Jr. Parreira et al., NEEL ORDER IN THE GROUND-STATE OF SPIN-1 2 HEISENBERG ANTIFERROMAGNETIC MULTILAYER SYSTEMS/, Journal of statistical physics, 86(5-6), 1997, pp. 1367-1371
We show existence of Neel order for the ground state of a system with
Ri two-dimensional layers with spin 1/2 and Heisenberg antiferromagnet
ic coupling, provided M greater than or equal to 8. The method uses th
e infrared bounds for the ground state combined with ideas introduced
by Kennedy, Lieb, and Shastry.