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Title: Unconventional continuous structural disorder at the order-disorder phase transition in the hexagonal manganites

Abstract

The improper ferroelectricity in YMnO 3 and other related multiferroic hexagonal manganites are known to cause topologically protected ferroelectric domains that give rise to rich and diverse physical phenomena. The local structure and structural coherence across the ferroelectric transition,however, were previously not well understood. Here we reveal the evolution of the local structure with temperature in YMnO 3 using neutron total scattering techniques, and interpret them with the help of first-principles calculations and with a first-principles-based effective Hamiltonian. The results show that, at room temperature, the local and average structures are consistent with the established ferroelectric P6 3 cm symmetry. On heating, both local and average structural analyses show striking anomalies from ~800K up to the Curie temperature and signatures of a locally more preserved structure than on average, consistent with increasing fluctuations of the order parameter angle. These fluctuations result in an unusual local symmetry lowering into a continuum of structures on heating. This local symmetry breaking persists into the high-symmetry non-polar phase,constituting an unconventional type of order-disorder transition, and we pinpoint it as the reason for the anomalous behaviour near the phase transition. The hidden disorder revealed in YMnO 3 by total scattering is expected to find analogiesmore » in other materials with structural frustration or characteristic energy barriers of different magnitudes.« less

Authors:
 [1]; ORCiD logo [2];  [3];  [4];  [3];  [5];  [1]
  1. NTNU Norwegian Univ. of Science and Technology, Trondheim (Norway)
  2. Brookhaven National Lab. (BNL), Upton, NY (United States)
  3. ETH Zurich, Zurich (Switzerland)
  4. Forschungszentrum Jülich, Julich (Germany); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  5. Brookhaven National Lab. (BNL), Upton, NY (United States); Columbia Univ., New York, NY (United States)
Publication Date:
Research Org.:
Brookhaven National Lab. (BNL), Upton, NY (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1530478
Alternate Identifier(s):
OSTI ID: 1524558
Report Number(s):
BNL-211732-2019-JAAM
Journal ID: ISSN 2160-3308
Grant/Contract Number:  
SC0012704
Resource Type:
Published Article
Journal Name:
Physical Review. X
Additional Journal Information:
Journal Volume: 9; Journal Issue: 3; Journal ID: ISSN 2160-3308
Publisher:
American Physical Society
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY

Citation Formats

Skjaervo, Sandra H., Bozin, Emil S., Meier, Quintin N., Feygenson, Mikhail, Spaldin, Nicola A., Billinge, Simon J. L., and Selbach, Sverre M. Unconventional continuous structural disorder at the order-disorder phase transition in the hexagonal manganites. United States: N. p., 2019. Web. doi:10.1103/PhysRevX.9.031001.
Skjaervo, Sandra H., Bozin, Emil S., Meier, Quintin N., Feygenson, Mikhail, Spaldin, Nicola A., Billinge, Simon J. L., & Selbach, Sverre M. Unconventional continuous structural disorder at the order-disorder phase transition in the hexagonal manganites. United States. doi:10.1103/PhysRevX.9.031001.
Skjaervo, Sandra H., Bozin, Emil S., Meier, Quintin N., Feygenson, Mikhail, Spaldin, Nicola A., Billinge, Simon J. L., and Selbach, Sverre M. Mon . "Unconventional continuous structural disorder at the order-disorder phase transition in the hexagonal manganites". United States. doi:10.1103/PhysRevX.9.031001.
@article{osti_1530478,
title = {Unconventional continuous structural disorder at the order-disorder phase transition in the hexagonal manganites},
author = {Skjaervo, Sandra H. and Bozin, Emil S. and Meier, Quintin N. and Feygenson, Mikhail and Spaldin, Nicola A. and Billinge, Simon J. L. and Selbach, Sverre M.},
abstractNote = {The improper ferroelectricity in YMnO3 and other related multiferroic hexagonal manganites are known to cause topologically protected ferroelectric domains that give rise to rich and diverse physical phenomena. The local structure and structural coherence across the ferroelectric transition,however, were previously not well understood. Here we reveal the evolution of the local structure with temperature in YMnO3 using neutron total scattering techniques, and interpret them with the help of first-principles calculations and with a first-principles-based effective Hamiltonian. The results show that, at room temperature, the local and average structures are consistent with the established ferroelectric P63cm symmetry. On heating, both local and average structural analyses show striking anomalies from ~800K up to the Curie temperature and signatures of a locally more preserved structure than on average, consistent with increasing fluctuations of the order parameter angle. These fluctuations result in an unusual local symmetry lowering into a continuum of structures on heating. This local symmetry breaking persists into the high-symmetry non-polar phase,constituting an unconventional type of order-disorder transition, and we pinpoint it as the reason for the anomalous behaviour near the phase transition. The hidden disorder revealed in YMnO3 by total scattering is expected to find analogies in other materials with structural frustration or characteristic energy barriers of different magnitudes.},
doi = {10.1103/PhysRevX.9.031001},
journal = {Physical Review. X},
number = 3,
volume = 9,
place = {United States},
year = {2019},
month = {7}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
DOI: 10.1103/PhysRevX.9.031001

Figures / Tables:

FIG. 1 FIG. 1: Structures of YMnO3 phases. (a) The high-symmetry nonpolar (NP) structure with purple MnO5 bipyramids and turquoise Y cations. Oxygens are shown in red. (b) The Landau free energy of the hexagonal manganites as a function of the two-component order parameter ($\mathcal{Q}$, Φ) resembling a Mexican hat, with themore » NP structure at the top. In the brim of the hat, the polar (P), antipolar (AP), and intermediate (IM) subgroup structures occur at the minima, maxima, and intermediate regions, respectively. (c) Group-subgroup relationship between the high-symmetry nonpolar structure and the subgroup structures found in the brim of the Mexican-hat energy landscape. (d) The order-parameter observables for the polar subgroup are the bipyramidal tilt amplitude (angles αA and αP) and corrugation of Y cations (ΔY). Note that ΔY denotes the distance in the c direction between Y1 and Y2. Green arrows indicate the directions of the bipyramidal tilts. The angle between the O1-O2 line and the c axis defines the apical tilt αA and is a robust measure of the order-parameter amplitude Q irrespective of the value of Φ. The plane through the three in-plane oxygens (one O3 and two O4) relative to the ab plane defines the planar tilt angle αP and is related to both the order-parameter amplitude Q and angle Φ. (e)–(g), Structures of the subgroups at different order-parameter angles Φ: Y off-centering pattern (top) and bipyramidal tilting directions, indicated by green arrows (bottom). Atomic sites for the three subgroups are labeled and coded with colored circles to emphasize which positions are symmetry related in each phase. Atom positions with the same color markings are aligned along the c axis and have the same multiplicity. A detailed overview of the atomic positions for the space groups is given in Fig. S1 of the Supplemental Material [26].« less

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      Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.