Exchange-bond structure and magnetization-step spectra of a diluted   Heisenberg antiferromagnet on the square lattice: Lopsided two-exchange   models
  Theoretycal results on the magnetization and susceptibility of a Heisenberg diluted antiferromagnet in the square lattice are given. The models considered have two exchange constants (J1-J2 and J1-J3) of which the second is much smaller than the first (lopsided models). Cluster statistics for clusters with up to 5 spins is given. A procedure to account for the contribution to the magnetization of clusters with more than 5 spins is described. 
Yaacov Shapira and Valdir Bindilatti