Magnetic order and finite-temperature properties of the two-dimensional frustrated Heisenberg model - art. no. 104406

Ground-state and finite-temperature properties of the square-lattice S=1/2 Heisenberg model with antiferromagnetic nearest- and next-nearest-neighbor interactions (J(1)-J(2) model) are investigated by a spin-rotation-invarian t Green's-function theory, where a reasonable agreement with numerical diag onalization data is found. The quantum phase transitions from the Neel and collinear phases into a spin-liquid phase are obtained at (J(2)/J(1))(c 1)= 0.24 and (J(2)/J(1))(c 2) =0.83, respectively, which considerably improves the results by a previous similar approach. The low-temperature magnetic su sceptibility at J(2)/J(1)less than or similar to0.5, the temperature of the susceptibility maximum, and the antiferromagnetic correlation length are f ound to decrease with increasing frustration. For high-T-c cuprates the rel ationship between the t-J model and an effective J(1)-J(2) model is analyze d.