One-dimensional mixed-spin Heisenberg antiferromagnet with single-ion anisotropy in a magnetic field: Thermodynamics

The S = 1 and S = 1/2 alternating Heisenberg antiferromagnetic spin chain with single-ion anisotropy in the presence of an applied magnetic field is investigated on the basis of the Schwinger bosom mean-field theory. The specific heat, the susceptibility and the magnetization as functions of temperature, the anisotropy as well as the applied held are discussed, respectively. The energy spectrum as a function of both the external field and the anisotropy is obtained. The results indicate that the single-ion anisotropy does not change so much the features of the specific heat, while the susceptibility the magnetization and the energy gaps are remarkably affected by the external field and the anisotropy. It is observed that with varying the external held a magnetization plateau exists at very low temperature. The system appears to exhibit a ferrimagnetic longe-range order for both h not equal 0 and D-1 not equal 0 in the ground state. Our results are compared with those obtained by other methods.