Johannes Richter, Heinz-Jürgen Schmidt
We consider a two-dimensional geometrically frustrated integer-spin Heisenberg system that admits an exact ground state. The system corresponds to a decorated square lattice with two coupling constants J1 and J2, and it can be understood as a generalized Shastry-Sutherland model. Main elements of the spin model are suitably coupled antiferromagnetic spin trimers with integer spin quantum numbers s and their ground state Phi will be the product state of the local singlet ground states of the trimers. We provide exact numerical data for finite lattices as well as analytical considerations to estimate the range of the existence in dependence on the ratio of the two couplings constants J2 and J1 and on the spin quantum number s. Moreover, we find that the magnetization curves as a function of the applied magnetic field shows plateaus and jumps. In the classical limit s \to \infty the model exhibits phases of three- and two-dimensional ground states separated by a one-dimensional (collinear) plateau state at 1/3 of the saturation magnetization.
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http://arxiv.org/abs/1202.5854
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