Spin fluctuations and structural modifications in frustrated multiferroics RMnO3 (R=Y, Lu) at high pressure

The crystal and magnetic structures of hexagonal manganites YMnO3 and LuMnO3 have been studied by powder neutron diffraction up to 6GPa in the temperature range of 10-300K. At ambient pressure, a triangular antiferromagnetic (AFM) state of a 1 irreducible representation is stable below TN=70K in YMnO3. Upon application of high pressure, a spin-reorientation was observed and the triangular AFM structure evolves from 1 to 1+2 representation symmetry. In LuMnO3, the triangular AFM state of a 2 symmetry with TN approximate to 95K remains stable in the investigated pressure range. The ordered Mn magnetic moment is suppressed at high pressure and low temperature, with much more pronounced effects for YMnO3, indicating enhanced spin fluctuations due to stronger magnetic frustration of the triangular lattice under higher pressure. The relationship between the evolution of spin fluctuations and in-plane Mn-O bonds under pressure is analyzed.