Effective easy-axis anisotropy of the two-sublattice single-chain magnet with twisted easy planes

An analytical solution for the spin-wave spectrum of the two-sublattice 1D magnet with S-A = S-B = 1 and twisting easy planes has been obtained. Such planes are mutually twisted by an angle phi relative to each other. For the case of mutually orthogonal easy planes phi = pi/2, the spectrum vs. quasi-momentum dependence has been compared with that of an easy-axis magnet with the easy axis aligned along the line of intersection of the planes. An analogy of the spectra of the models has been shown, indicating the possibility of the effective easy axis anisotropy in easy-plane two-sublattice single-chain magnets.