Magnetic susceptibility of a CuO2 plane in the La2CuO4 system:: I.: Random-phase approximation treatment of the Dzyaloshinskii-Moriya interactions -: art. no. 214418

Motivated by recent experiments on undoped La2CuO4, which found pronounced temperature-dependent anisotropies in the low-field magnetic susceptibility, we have investigated a two-dimensional square lattice of S=1/2 spins that interact via Heisenberg exchange plus the symmetric and antisymmetric Dzyaloshinskii-Moriya anisotropies. We describe the transition to a state with long-ranged order and find the spin-wave excitations, with a mean-field theory, linear spin-wave analysis, and using Tyablikov's random-phase approximation decoupling scheme. We find the different components of the susceptibility within all of these approximations, both below and above the Neel temperature, the latter using the method of Lee and Liu, and obtain evidence of strong quantum fluctuations and spin-wave interactions in a broad temperature region near the transition.