Effects of the geometric frustration on the ground-state and thermodynamic properties of the spin-1 Heisenberg model for an isotropic triangular lattice

We study the ground state and thermodynamic properties of the spin-1 antiferromagnetic Heisenberg model on an isotropic triangular lattice with nearest-neighbor J1 and next-nearest-neighbor J2 exchange interactions. The auxiliary fermionic representation of spin operators within the Popov-Fedotov functional integral formalism is used to calculate thermodynamic quantities. The Luttinger-Tisza procedure is used to represent the classical ground state energy in term of the magnetic order vector Q, which allows considering the contribution of fluctuations to the free energy of the system. The results obtained are compared with those of linear spin wave approximation and other methods. The effect of magnetic frustration on the sublattice magnetization, energy excitation spectrum and specific heat of the ordered magnetic phase will also be discussed in detail.