Schwinger-boson mean-field theory of an anisotropic ferrimagnetic spin chain

By using the Schwinger-boson mean-field theory, the Heisenberg ferrimagnetic spin chain with the single-ion anisotropy D is explored. Based on the effect of the single-ion anisotropy D, we obtain four branches of the low-lying excitation and calculate the anisotropy dependence of spin reduction and the longitudinal correlation at zero temperature. We also discuss the free energy, magnetic susceptibility and specific heat at finite temperature with different anisotropy D.