Spin-Wave Instabilities and Noncollinear Magnetic Phases of a Geometrically Frustrated Triangular-Lattice Antiferromagnet

Using a combination of phenomenological and Monte Carlo techniques, we examine in detail the relationship between spin-wave instabilities of the collinear magnetic phases and the resulting noncollinear phases for a geometrically frustrated triangular-lattice antiferromagnet. We demonstrate that the instability wave vector with the strongest intensity for the collinear phase dictates the ordering wave vector of the cycloid or complex noncollinear phase. The completed phase diagram for triangular-lattice antiferromagnet including the cycloid and noncollinear phases is shown in the right. Our results are related to the experimentally observed multiferroic phase of Al doped CuFeO₂. This work was done by J. T. Haraldsen and R. S. Fishman in collaboration with G. Alvarez at CSMD & CNMS, ORNL and M. Swanson at North Dakota State University. Phys. Rev. Lett. 102, 237204 (2009)