Magnetic properties of the spin-1 heisenberg antiferromagnet on an interpolating square – triangular lattice in Popop-Fedotov representation

We study the S=1 anisotropic antiferomagnetic Heisenberg model on a square lattice for all temperatures using the Popov-Fedotov representation of spin operators. In this representation the constraint of single particle site occupation is rigorously fulfilled by introducing an imaginary valued chemical potential.