Possible phase transition of anisotropic frustrated Heisenberg model at finite temperature

The frustrated spin-1/2 J 1 a - J 1 b - J 2 antiferromagnet with anisotropy on the two-dimensional square lattice was investigated, where the parameters J 1 a and J 1 b represent the nearest neighbor exchanges and along the x and y directions, respectively. J 2 represents the next-nearest neighbor exchange. The anisotropy includes the spatial and exchange anisotropies. Using the double-time Green's function method, the effects of the interplay of exchanges and anisotropy on the possible phase transition of the Néel state and stripe state were discussed. Our results indicated that, in the case of anisotropic parameter 0≤ η J 1 b /2, a first-order phase transformation between the two states may also occur. However, for J 2< J 1 b /2, the Néel state is always more stable than the stripe state.