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 w ith single-ion anisotropy in the presence of an applied magnetic field is i nvestigated on the basis of the Schwinger bosom mean-field theory. The spec ific heat, the susceptibility and the magnetization as functions of tempera ture, the anisotropy as well as the applied held are discussed, respectivel y. The energy spectrum as a function of both the external field and the ani sotropy is obtained. The results indicate that the single-ion anisotropy do es not change so much the features of the specific heat, while the suscepti bility the magnetization and the energy gaps are remarkably affected by the external field and the anisotropy. It is observed that with varying the ex ternal held a magnetization plateau exists at very low temperature. The sys tem appears to exhibit a ferrimagnetic longe-range order for both h not equ al 0 and D-1 not equal 0 in the ground state. Our results are compared with those obtained by other methods.