Entangled spin clusters: Some special features

In this paper, we study three specific aspects of entanglement in small spin clusters. We first study the effect of inhomogeneous exchange coupling strengths on the entanglement properties of the S=1/2 antiferromagnetic linear chain tetramer compound NaCuAsO₄. The entanglement gap temperature T_E is found to have a nonmonotonic dependence on the value of α, the exchange coupling inhomogeneity parameter. We next determine the variation of T_E as a function of S for a spin dimer, a trimer, and a tetrahedron. The temperature T_E is found to increase as a function of S but the scaled entanglement gap temperature t_E goes to zero as S becomes large. Last, we study a spin-1 dimer compound to illustrate the quantum complementarity relation. We show that in the experimentally realizable parameter region, magnetization and entanglement plateaus appear simultaneously at low temperatures as a function of the magnetic field. Also, the sharp increase in one quantity as a function of the magnetic field is accompanied by a sharp decrease in the other so that the quantum complementarity relation is not violated.