Magnetic soft modes in the distorted triangular antiferromagnet alpha-CaCr(2)O(4)

Abstract

In this Letter, we explore the phase diagram and excitations of a distorted triangular lattice anti-ferromagnet. The unique two-dimensional distortion considered here is very different from the "isosceles''- type distortion that has been extensively investigated. We show that it is able to stabilize a 120 degrees spin structure for a large range of exchange interaction values, while new structures are found for extreme distortions. A physical realization of this model is alpha-CaCr(2)O(4), which has a 120 degrees structure but lies very close to the phase boundary. This is verified by inelastic neutron scattering which reveals unusual rotonlike minima at reciprocal space points different from those corresponding to the magnetic order. © 2012 The American Physical Society