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Study of Double-Layer Heisenberg Antiferromagnetic Systems

A double-layer square lattice Heisenberg antiferromagnetic system is studied by using Green's function technique. It is shown that the sublattice magnetization increases with the increase of the antiferromagnetic interlayer exchange coupling for small , while it turns to decrease for large . In contrast to the conventional spin-wave calculations, there always exists a finite zero-temperature staggered magnetisation. The transition from the antiferromagnetic phase to disordered phase is also discussed.