Phases of the spin-21 Heisenberg antiferromagnet on the diamond-decorated square lattice in a magnetic field
Heisenberg model has long been an interesting and intensive research topic owing to its intrinsic theoretical interest and potential application in many areas. Understanding non-equilibrium system of the Heisenberg antiferromagnet might promote our understanding of magnetic system and give us theoretical background on quantum signal manipulation. In this thesis, we consider the Heisenberg antiferromagnet in time periodic magnetic field using the Classical Spin Wave Theory and the Schwinger Boson Theory. The spin-spin response functions for the Heisenberg antiferromagnet in 2 cases of time periodic field were obtained, including case (1) B⃗0(t) = Bo(t)ẑ, where B0(t) is a periodic magnetic field in time, and (2) B⃗0(t) = Bo(cos(Ωt)x̑+sin(Ωt)ŷ). In the Classical Spin Wave Theory, the spin-spin response function and absorption spectrum of spin wave are obtained. In the Schwinger Boson Theory, the spin-spin response calculation gives same result to its classical analog. The 1/S quantum correction factor is shown to be identical to that of case when time dependent magnetic field is absent.