High-pressure effect on the crystal and magnetic structures of the frustrated antiferromagnet YMnO3

Abstract

The high-pressure (to 5 GPa) effect on the crystal and magnetic structures of the hexagonal manganite YMnO3 is studied by neutron diffraction in the temperature range 10–295 K. A spin-liquid state due to magnetic frustration on the triangular lattice formed by Mn ions is observed in this compound at normal pressure and T > TN = 70 K, and an ordered triangular antiferromagnetic state with the symmetry of the irreducible representation Γ1 arises at T < TN. The high-pressure effect leads to a spin reorientation of Mn magnetic moments and a change in the symmetry of the antiferromagnetic structure, which can be described by a combination of the irreducible representations Γ1 and Γ2. In addition, it is observed that the ordered magnetic moment of Mn ions decreases from 3.27 μB (5 GPa) to 1.52 μB (5 GPa) at T = 10 K and diffuse scattering is enhanced at temperatures close to TN. These effects can be explained within the model of the coexistence of the ordered antiferromagnetic phase and the spin-liquid state, whose volume fraction increases with pressure due to the enhancement of frustration effects.