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Abstract:
The Heisenberg model on a triangular lattice is a prime example of a
geometrically frustrated spin system. However most experimentally
accessible compounds have spatially anisotropic exchange interactions.
As a function of this anisotropy, ground states with different magnetic
properties can be realized. Motivated by recent experimental findings on
Cs2CuCl4-xBrx, we discuss the full phase diagram of the anisotropic
model with two exchange constants J(1) and J(2), including possible
ferromagnetic exchange. Furthermore a comparison with the related square
lattice model is carried out. We discuss the zero-temperature phase
diagram, ordering vector, ground-state energy, and ordered moment on a
classical level and investigate the effect of quantum fluctuations
within the framework of spin-wave theory. The field dependence of the
ordered moment is shown to be nonmonotonic with field and control
parameter.
