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

Abstract

The crystal and magnetic structures of hexagonal manganites YMnO₃ and LuMnO₃ have been studied by powder neutron diffraction up to 6 GPa in the temperature range of 10–300 K. At ambient pressure, a triangular antiferromagnetic (AFM) state of a Γ₁ irreducible representation is stable below T _N=70 K in YMnO₃. Upon application of high pressure, a spin-reorientation was observed and the triangular AFM structure evolves from Γ₁ to Γ₁+Γ₂ representation symmetry. In LuMnO₃, the triangular AFM state of a Γ₂ symmetry with T _N ≈ 95 K 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.

Keywords:

• spin liquid
• multiferroics
• neutron diffraction
• high pressure
• phase transitions
• magnetic frustration

Acknowledgements

The work was supported by Russian Foundation for Basic Research, grant 09-02-00311a and a grant from the President of the Russian Federation MD-696.2010.2 and state contract 02.740.11.0542. Works at SungKyunKwan University were supported by the Korea Research Foundation (Grant No. KRF-2008-220-C00012), and the KOSEF (Grant No. R17-2008-033-01000-0 and No. R31-2008-000-10029-0).