Ground-state properties of an S=1/2 Δ-chain with ferro- and antiferromagnetic interactions

Using numerical methods, we investigate the ground-state properties of an S = 1/2 Delta-chain in which the nearest-neighbor exchange interactions between apical and basal spins are ferromagnetic and those between basal spins are antiferromagnetic. We,find that the ground state of the system is the ferromagnetic or the ferrimagnetic state depending,on whether the former interaction constant is larger or smaller than the twice of the latter one. We also discuss the ground-state :magnetization curve of the system in connection with experimental results for [Cu(bpy)H2O][Cu(bpy)(mal)H2O](ClO4)(2). (C) 2004 Elsevier B.V. All rights reserved.