The magnetic structures of hexagonal manganites
YMnO3
and LuMnO3
have been studied by powder neutron diffraction up to 6 GPa in the temperature range
10–295 K. At ambient pressure, a triangular antiferromagnetic (AFM) state of a
Γ1 irreducible representation
is stable below TN = 70 K
in YMnO3. Upon
the application of high pressure, a spin reorientation is induced and the triangular AFM structure evolves
from Γ1
to Γ1+Γ2
representations. On the other hand, in
LuMnO3 the triangular AFM
state of a Γ2 irreducible
representation with TN≈90 K
remains stable over the entire pressure range investigated. The
ordered magnetic moment values decrease under pressure with
dM/dP = −0.35 μB GPa−1 in
YMnO3
and −0.08 μB GPa−1
in LuMnO3. Simultaneously, a considerable increase in diffuse scattering intensity was found in
YMnO3, while it was much
less pronounced for LuMnO3. Both features indicate the enhancement of spin fluctuations due to geometrical
frustration effects and an increase in the volume fraction of the spin-liquid state
coexisting with the ordered AFM phase. The characteristic spin correlation length
is weakly affected by pressure. The relationship between the pressure-induced
behaviour of magnetic structure and the structural characteristics of the
quasi-two-dimensional (2D) triangular network formed by Mn and O ions in hexagonal
RMnO3
is analysed.
We investigated the magnetic structure and short-range spin correlations of multiferroic hexagonal manganite YMnO 3 by powder neutron diffraction at high pressures up to 6.7 GPa. High pressure induces a spin-liquid phase in multiferroic YMnO 3 , coexisting with the suppressed long-range antiferromagnetic order. This spinliquid phase exhibits a temperature dependence distinctively different from short-range spin correlations seen at ambient pressure. Its formation occurs through an in-plane Mn-O bond symmetrization and results in reduced magnetoelastic coupling at high pressures.
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