“Supersolid” phase in spin-1 easy-plane antiferromagnetic

The phase states are investigated for the spin-1 two-sublattice antiferromagnetic with strong easy-plane single-ion anisotropy, exceeding the exchange interaction, in an external magnetic field. Two cases of field orientation are considered: perpendicular to the easy-plane, and in-plane orientation. The analysis of spectra of elementary excitations allows determining the lines of the phase transitions and their types. The (H, D) phase diagram is built for both orientations of the magnetic field. It is shown that the magnetization of sublattices reaches saturation only at infinitely large field, if it is oriented in-plane. This is related with the fact that the spin magnetic moment is not integral of motion in such geometry