Partial glass isosymmetry transition in multiferroic hexagonal<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>ErMn</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>

Barbour, Andi; Alataş, Ahmet; Liu, Y.; Zhu, Chenhui; Leu, Bogdan M.; Zhang, X.; Sandy, Alec; Pierce, Michael S.; Wang, Xueyun; Cheong, Sang‐Wook; You, Hoydoo

doi:10.1103/physrevb.93.054113

Cited by 7 publications

(4 citation statements)

References 41 publications

(46 reference statements)

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“…The onset of structural fluctuations above 800 K coincides with the temperature of previously reported anomalies in lattice parameters and polarisation 12,15,23,34 . Our analysis of PDFs from ambient to above T C provides a local structure explanation for these anomalies, and also rules out a second macroscopic phase transition.…”

Section: Discussionsupporting

confidence: 85%

Unconventional Continuous Structural Disorder at the Order-Disorder Phase Transition in the Hexagonal Manganites

et al. 2019

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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. The results show that, at room temperature, the local and average structures are consistent with the established ferroelectric P 63cm symmetry. On heating, both local and average structural analyses show striking anomalies from ∼ 800 K up to the Curie temperature 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.arXiv:1707.09649v2 [cond-mat.mtrl-sci]

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Section: Discussionsupporting

confidence: 85%

Unconventional Continuous Structural Disorder at the Order-Disorder Phase Transition in the Hexagonal Manganites

et al. 2019

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“…While their specific origin still remains a puzzle (being detected with three independent set ups and techniques rules out the possibility of an interferometer or detector artifact) we may reason of these are due to the strong anisotropies between the Rare Earth and oxygens involved in plane buckling and bipyramid tilting in conjunction with the dynamics emerging from the c axis negative thermal expansion 49 and, perhaps, also associated to reinforcing ferroelectricity being the 4f 11 -3d 4 interplay a known player in polar ordering 45 in an on-going process with imperfect (√3x√3)R30° structural ordering. 50 It points to a symmetry allowed lattice phonon interactions with 4f electrons associated to ground Er 3+ crystal field levels that is better seen at low temperatures due to the increase in their population. Very recently, Singh et al 51 reported that in double perovskite Nd2ZnIrO6 low lying excitations amount to strong coupling between phonons and Nd 3+ 4f 3 crystal field excitations raising the possibility that all these magnetic and lattice degrees of freedom have common grounds that might also be shared by features found in HoMnO3 (Ref.…”

Section: A Low-frequency Phonons Magnetic Excitations and Er 3+ Cryst...mentioning

confidence: 93%

h−ErMnO3 absorbance, reflectivity, and emissivity in the terahertz to mid-infrared from 2 to 1700 K: Carrier screening, Fröhlich resonance, small polarons, and bipolarons

et al. 2020

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We report the temperature dependent THz to mid-infrared response of hexagonal-ErMnO3 using absorption, reflectivity, and emissivity techniques from 2 K to 1700 K. At low temperatures, lowest frequency vibrational modes which extend up the lock-in ferroelectric temperature, coexist with paramagnon excitations and are associated with well-defined crystal field Rare Earth pure magnetic replicas in an intriguing phonon-magnetic convergence enhancing the multiferroic character of h-ErMnO3. Increasing the temperature, a number of vibrational bands close to the space group predicted undergo profile broadening and softening. In particular, a distinctive set of bands in the 288-329 cm -1 (300 K) range has a component whose profile is carrier screened becoming nearly fully blurred in the intermediate phase between ~830 K and ~1500 K. Below TC ~830 K this asymmetric band, having one component still partially screened, further splits as spin phonon interaction and the tripling of the unit cell takes place revealing at TN ~79 K a delicate balance of long-and short-range interactions. Ambient Raman scattering brings up evidence of a Fröhlich resonance due to Coulomb interactions between carriers and the macroscopic field linked to the corresponding longitudinal optical phonon mode. We found it is dynamically correlated to the hexagonal c-axis negative thermal expansion. Quantitative analyses of the mid-infrared (MIR) optical conductivity show that also plays a role in small polarons and mediates in high temperature bipolarones.Bipolaron profiles at high temperatures change as the sample opacity increases when at ~900 K straight stripes turn curly toward complex vortex-antivortex domain patterns in the paraelectric phase. At still higher temperatures a low frequency Drude contribution is triggered by electron hopping signaling an insulator-metal phase transition at ~1600 K while the MIR response suggests coexistence between single small polarons and bipolarons. On closing, we draw a parallel with improper ferroelectrics sustaining a lattice incommensurate intermediate phase and unit cell tripling. We argue that in the h-RMnO3 (R=Rare Earth, Y) family of compounds the intermediate phase be considered incommensurate with onset at TINC ~1500 K and ferroelectric lock-in at TC ~830 K delimiting this regime in h-ErMnO3.

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“…Previously reported values of activation energy for the migration of ferroelectric domain walls in YMnO3 and ErMnO3 include 0.24 eV [61] and 0.54 eV [64] respectively. The loss peak in Q -1 is therefore also likely to be due to pinning/unpinning of some aspect of the ferroelectric domain structure which remains mobile under the low stress, high frequency conditions of an RUS experiment only above ~250 K. Changes induced in the ferroelectric domain wall configurations or whatever changes of other defects that occur as a consequence of cycling through the AFM -FIM transition relax back to the starting state after the crystals are heated back to temperatures above the (frequency-dependent) freezing/pinning temperature.…”

Section: Domain Wall Pinning/relaxationmentioning

confidence: 99%