FRUSTRATION AND ZERO-POINT MOTION IN HEISENBERG BODY-CENTERED TETRAGONAL ANTIFERROMAGNETS

Body-centred tetragonal (BCT) antiferromagnets are a central topic of both theoretical and experimental research. The Heisenberg BCT antiferromagnet shows full frustration induced by the lattice structure for all physically meaningful values of the exchange parameters. A previous analysis of the minimum-energy configuration indicated full frustration only if no coupling between next-nearest-neighbour planes is present. However, the analysis was restricted to a classical helix configuration whereas infinite non-helical configurations characterized by an arbitrary angle between the spin at the centre and the spins at the corner minimize the classical energy of the model in a substantial part of the parameter space. In any case the relevance of quantum fluctuations in solving the infinite degeneracy is confirmed. The first quantum correction to the magnon energy spectrum is shown to lift the degeneracy of the soft lines which are present in the classical approximation. © 1990 IOP Publishing Ltd.