Abstract
The spin-1 antiferromagnetic Heisenberg model was investigated by
the introduction of spin operators on a square lattice in terms of a mean-field approximation (MFA). The bilinear exchange interaction parameters Jx and Jz, the crystal field
interactions Dx and Dz, and the external magnetic field components Hx and Hz along
the x- and z-axes were all incorporated in the model Hamiltonian. The effects of the
Dzyaloshinskii-Moriya interaction (DMI), ∆m, were also included along the y-axis,
i.e. containing the spin components only along the x- and z-axis. Various phases of the
model, including ferromagnetic (FM), antiferromagnetic (AFM), and random (R) were
identified by studying the thermal variations of the order-parameters, susceptibilities,
specific heats, and free energy of the sublattices. The second-order phase transition temperatures between these phases were identified, in addition to the existence of first-order
phase transitions. Numerous critical points, including the three-phase coexistence, were
observed on the phase diagrams. The reentrant behavior was also seen for appropriate
values of the system parameters.