Abstract
Neutron-scattering experiments probe changes in atomic structure of the multiferroic hexagonal manganite YMnO${}_{3}$ during its structural phase transition and find signatures of a new type of transition that could explain some of the material's unusual electric behavior.
Highlights
The multiferroic hexagonal manganites, h-RMnO3 (R 1⁄4 Dy-Lu, In, Y, or Sc), are improper ferroelectrics where the polarization emerges as a secondary effect due to an improper coupling to the primary distortion mode
We discovered unconventional behavior across the improper ferroelectric transition in the hexagonal manganites where the amplitude of the two-dimensional order parameter is order-disorder-like, but the order-parameter angle behaves displacively
This unusual behavior is indicated by our finding that the local structure across TC differs strongly from the established average structure symmetry and that the local low-symmetry distortions are conserved in the high-symmetry phase, both evidence of an order-disorder mechanism
Summary
The multiferroic hexagonal manganites, h-RMnO3 (R 1⁄4 Dy-Lu, In, Y, or Sc), are improper ferroelectrics where the polarization emerges as a secondary effect due to an improper coupling to the primary distortion mode. Studies based on powder neutron [12,13] and x-ray [13,14,15,16,17,18] diffraction show good agreement with a polar model describing the average structure at low and intermediate temperatures, while structural anomalies have been reported between 800 K and the Curie temperature TC These findings led to a range of reported values for TC and proposals of two distinct structural phase transitions [12,13,14,15,16,19], it is understood that there is only one phase transition at TC, with the polarization slowly emerging as a secondary effect [20,21,22,23,24]
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