Ferromagnetism in the XXZ chain with next-nearest-neighbor interactions

We study the total magnetization M of the one-dimensional spin−1/2 XXZ model with ferromagnetic nearest-neighbor (NN) exchange interactions J1 and antiferromagnetic next-NN J2, with corresponding anisotropies Δi. Near the isotropic limit, the model is expected to be relevant for quasi one-dimensional cuprates containing edge-sharing CuOn polyhedra. By numerical diagonalization of finite chains, we construct a phase diagram separating the regions of parameters for which M=0 from those in which the system is ferromagnetic (M≠0) with maximum possible M or intermediate M.