Spin excitations in La2CuO4:: Consistent description by inclusion of ring exchange -: art. no. 100403

We consider the square lattice Heisenberg antiferromagnet with plaquette ring exchange and a finite interlayer coupling leading to a consistent description of the spin-wave excitation spectrum in La2CuO4. The values of the in-plane exchange parameters, including ring exchange J(square), are obtained consistently by an accurate fit to the experimentally observed in-plane spin-wave dispersion, while the out-of-plane exchange interaction is found from the temperature dependence of the sublattice magnetization at low temperatures. The fitted exchange interactions J=151.9 meV and J(square)=0.24J give values for the spin stiffness and the Neel temperature in excellent agreement with the experimental data.