Magnetization steps and cluster-type statistics for a diluted Heisenberg   antiferromagnet on the square lattice: Models with two exchange constants
  The paper presents theoretical results on the magnetization of a diluted Heisenberg antiferromagnet on the square lattice for models with two exchange constants (J1-J2 and J1-J3). Cluster with up to five spins (5/2) are considered. 
Yaacov Shapira and Valdir Bindilatti