S. G. Condran, M. L. Plumer
Symmetry arguments are used to develop a spin Hamiltonian for the description
of the complex magnetic ordering in HoMnO$_3$. Using a novel application of the
Landau Lifshitz Gilbert dynamic torque equations to this model of the
frustrated Mn ions on an $AB$ stacked triangular antiferromagnetic, it is shown
that the four principal spin configurations observed in this compound are
stabilized. Ho-Mn coupling is found to be a consequence of an unusual trigonal
anisotropy term which is responsible for simultaneous Mn spin reorientation and
onset of Ho magnetic order. Based on these microscopic considerations, a
mean-field Landau-type free energy is derived which reproduces the succession
of observed temperature driven magnetic phase transitions at zero field,
including re-entrant behavior. In addition, our analysis suggests that the
basal-plane magnetic order should be slightly incommensurate with the lattice.
View original:
http://arxiv.org/abs/1202.2321
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