Phase Diagram of Spin-1/2 Alternating Ferromagnetic Chain with XY-Like Anisotropy

Abstract

By the use of the numerical method we investigate the ground state phase diagram of spin-1/2 alternating ferromagnetic chain. We numerically diagonalized the Hamiltonian of finite systems (up to 20 spins) and analyzed the numerical data for various physical quantities using the finite size scaling and the extrapolation methods. The ground state is either the effective singlet (ES) state or the spin fluid (SF) state depending on the value of the alternation parameter δ and the anisotropy parameter Δ≡J_z⁄J_⊥(Δ=−1 for the isotropic ferromagnetic case and Δ=0 for the XY case). The phase diagram obtained in this work strongly stupports the theoretical studies of Kohmoto-den Nijs-Kadanoff and Okamoto-Sugiyama. We also discuss the critical properties near the ES–SF transition line.