Ground State and Excitation Spectrum of a Spin-1/2 Ising-Like Ferromagnetic Chain with Competing Interactions

Abstract

Excitation spectrum as well as ground states is studied in detail in the region near the Ising limit with small XY-component in a Heisenberg ferromagnetic chain with competing antiferromagnetic second-neighbor interaction. A spin-fluid-like phase with gapless excitation spectrum, which exhibits ferromagnetic long-range order, is derived in the intermediate region between the saturated ferromagnetic and (2, 2) antiphase states, by mapping onto a system of Bose-like particles with hard core of finite radius. Expressions for the magnetization, the susceptibility and the dispersion relalion of the excitation spectrum are obtained in the intermediate phase. This mapping is expected to be exact in the region near the degenerate point.