Abstract

Two-dimensional triangular lattice has been the source of rich physics with its generic frustration effects. We have investigated the spin-lattice coupling and magnetism of the two-dimensional triangular lattice in hexagonal RMnO3. Hexagonal RMnO3 belongs to a class of multiferroic materials with both ferroelectric and antiferromagnetic transitions in a single compound. One of salient features of RMnO3 is that Mn ions form a natural 2D triangular lattice with a noncollinear 120 structure. In this talk, I will present our works conducted over the past few years, where we have addressed mainly two issues: (i) the origin of magnetoelectric coupling and (ii) the spin waves. First, by using high-resolution neutron and synchrotron diffraction studies we demonstrated that a strong spin-lattice coupling lies at the heart of the magnetoelectric coupling in these compounds. Second, I will discuss how the spin waves measured by inelastic neutron scattering techniques allowed us to not only confirm the existence of a strong spin-lattice coupling but also unravel unusual nonlinear magnon interaction effects in these materials somewhat unexpectedly.