Low-Temperature Thermodynamic Properties Of The Heisenberg Antiferromagnetic Chain With Two Easy-Axis Single-Ion Anisotropies

In this paper, the spin wave theory is applied to the one-dimensional Heisenberg antiferromagnet in the coexistence of two different anisotropies D-1 and D-2, which are separately the easy-axis single-ion anisotropies for sublattice A and sublattice B of the system. Both the ground-state and low-temperature properties of the system are strongly affected by the competition between these two anisotropies. Two kinds of the competition in terms of the deviation parameter Delta = D-1 - D-2 are discussed for the uniform anisotropy taking the values of D = D-1 and D = (D-1 + D-2)/2, respectively. The Delta-dependent behaviors (such as the power, exponential and linear laws) are obtained for the total magnetization, the staggered magnetizations, the internal energy, the specific heat and the susceptibility. It is found that at zero-temperature, the interplay between these two anisotropies induces the antiferromagnetic-disorder phase transition in the small anisotropy region with D-1 not equal D-2. For the selected cases of D-1 = D-2, our results for are in agreement with the findings obtained by the existing theories and the quantum Monte Carlo data.