Abstract
The effects of quantum fluctuations due to directional anisotropy and frustration between nearest neighbors and next-nearest neighbors of the quantum spin-1/2 Heisenberg antiferromagnet on a square lattice are investigated using spin-wave expansion. We have calculated the spin-wave energy dispersion in the entire Brillouin zone, renormalized spin-wave velocities, and the magnetization up to second order in 1/S expansion for the antiferromagnetic Neel and collinear antiferromagnetic stripe phases. It is shown that the second-order corrections become significant with increase in frustration. With these corrections magnetizations and spin-wave velocities for both the phases become zero at the quantum critical points as expected from other numerical and analytical methods. We have shown that the transition between the two ordered phases are always separated by the disordered paramagnetic phase.
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