The two-dimensional S = 1/2 (or quantum) Heisenberg antiferromagnet (2D QHAF) forms the magnetic skeleton of the superconducting copper oxides such as La2-xSrxCuO4+d with the strong magnetic interactions purported to play a prominent role in the formation of Cooper pairs. While the zero-field properties of the 2D QHAF have been examined in depth, very little is know of the effects of external fields upon its behavior. Recent theoretical predictions* predict a strong field dependence of the energy spectrum. I will describe two structures and properties of two new families of molecular-based 2D QHAF with moderate exchange strengths in which the field-dependent properties can be examined in detail. *Zhitomirsky and Chernyshev, PRL 82, 4536 (1999); Syljuåsen and Lee, PRL 88, 207207 (2002).
Clark University, Worcester, Massachusetts (USA)