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arXiv · 0710.1251

Biconical structures in two-dimensional anisotropic Heisenberg antiferromagnets

M. Holtschneider·W. Selke
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Abstract

Square lattice Heisenberg and XY antiferromagnets with uniaxial anisotropy in a field along the easy axis are studied. Based on ground state considerations and Monte Carlo simulations, the role of biconical structures in the transition region between the antiferromagnetic and spin--flop phases is analyzed. In particular, adding a single--ion anisotropy to the XXZ antiferromagnet, one observes, depending on the sign of that anisotropy, either an intervening biconical phase or a direct transition of first order separating the two phases. In case of the anisotropic XY model, the degeneracy of the ground state, at a critical field, in antiferromagnetic, spin--flop, and bidirectional structures seems to result, as in the case of the XXZ model, in a narrow disordered phase between the antiferromagnetic and spin--flop phases, dominated by bidirectional fluctuations.

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M. Holtschneider, W. Selke. 2007-12-19. Biconical structures in two-dimensional anisotropic Heisenberg antiferromagnets. https://doi.org/10.1103/physrevb.76.220405

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