Department of Physics, Sungkyunkwan University
Hexagonal manganites RMnO3 show ferroelectric transitions at very high temperatures, some of them above 700 K, while they order antiferromagnetically below 100 K. This coexistence of both ferroelectric and antiferromagnetic transitions in a single compound, so-called multiferroic behavior, is a rare phenomenon and has been the subject of recent intensive studies. Another interesting point about the magnetic properties of the rare-earth hexagonal manganites is that the Mn moments form natural two-dimensional edge-sharing triangular networks. Although some of early studies, including neutron diffraction experiments, were carried out in 60s on these materials, with the renewed interests in multiferroic behavior the physical properties of the hexagonal manganites have been reinvestigated. In this talk, we will present our recent works on several hexagonal manganites using both neutron scattering and bulk properties. Key points that will be covered in the talk are: First, we will discuss experimental evidence of spin frustrations observed in both neutron scattering and bulk measurements. Second, we will examine experimental results due to an unusually strong spin-lattice coupling. Third, we will show how the magnetic ground states of RMnO3 change upon chemical doping and external pressure.