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

Skjærvø, Sandra Helen; Meier, Quintin N.; Feygenson, Mikhail; Spaldin, Nicola A.; Billinge, Simon J. L.; Božin, Emil S.; Selbach, Sverre M.

doi:10.1103/physrevx.9.031001

Cited by 44 publications

(48 citation statements)

References 72 publications

(78 reference statements)

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“…First the system breaks Z 3 symmetry, indicated by the decrease of vortex density, then the system breaks Z 2 symmetry, leading to non-zero polarization. This two-step nature of the ferroelectric transition in RMnO 3 has been observed experimentally [25]. The lattice responds to external electric field is in agreement with experimental results [15,16,26].…”

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confidence: 88%

A Monte-Carlo Study on the Coupling of Magnetism and Ferroelectricity in the Hexagonal Multiferroic RMnO3

2018

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The ferroelectric phase transition in RMnO 3 breaks both Z 3 and Z 2 symmetries, giving rise to 6 structural domains. Topological protected vortices are formed at the junctions of all 6 domains, and the ferroelectric phase transition is closely related to these Z 6 vortices. In this work, Monte-Carlo studies on both the ferroelectric and magnetic transition have been performed on RMnO 3 system. The magnetic simulation results on lattices with different structural domain distributions induced by external electric field and simulated quenching show different magnetic transition temperature T s , indicating that the coupling of magnetism and ferroelectricity is through the Z 6 structural domain. At extreme case, lattice quenched from above the ferroelectric transition results in high vortex density, which can drive the system into spin glass.Multiferroics are materials that host magnetism and ferroelectricity in a single phase [1]. The potential of having magnetism and ferroelectricity coupling makes these materials of great importance both technologically and scientifically. Judging by the source of magnetism and ferroelectricity, multiferroics can be categorized into type-I and type-II: in type-I multiferroics the magnetism and ferroelectricity have different origins and are often well separated in transition temperatures, whereas in type-II multiferroics the magnetism is the cause of ferroelectricity [2][3][4]. As a typical type-I multiferroic, the hexagonal RMnO 3 (R = Y, Lu, Sc, · · · ) becomes ferroelectric below T C ∼ 570-990 K when the crystal breaks the Z 3 symmetry of the high temperature P6 3 mmc phase through a structural instability of the Mn and O atoms due to trimerization [5][6][7]. The trimerization then leads to the rare earth atom splitting into two atomic sites which breaks the Z 2 symmetry and gives rise to polarization, as illustrated in Figure 1b. The space group of the ferroelectric phase is P6 3 cm [8]. Since the Mn atoms form triangular lattice in the xy-plane, the system becomes geometrically frustrated [9]. Below T N ∼ 90 K, the magnetic moment of Mn orders in a 120 • arrangement [8,10]. The weak interaction between magnetism and ferroelectricity in RMnO 3 was observed through in-plane dielectric anomaly [11].The Z 3 × Z 2 symmetry breaking in the ferroelectric transition of RMnO 3 creates 6 structural domains. As shown in Figure 1a-c, RMnO 3 consists of corner sharing MnO 5 bipyramid layers separated by the rare earth atom layers. From the top view, each MnO 5 bipyramid is surrounded by 3 rare earth atoms (α, β, γ). The trimerization involves tilting of the bipyramids towards one of the 6 symmetry equivalent directions: α + , β + , γ + , α − , β − , γ − , each of which corresponds to a structural domain [6]. This has been confirmed by observations using optics second harmonic generation, SEM, STM and AFM [6,[12][13][14][15][16]. Both the magnetic and ferroelectric order parameters are confined in the xy-plane due to the crystal geometry [17]. Based on this feature, a 2D 6-fold clock mode...

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confidence: 88%

A Monte-Carlo Study on the Coupling of Magnetism and Ferroelectricity in the Hexagonal Multiferroic RMnO3

2018

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“…4 for ErMnO 3 . The excellent agreement with experiment [42] suggests that the quasiharmonic population of phonons with increasing temperature is the dominant contribution to the thermal evolution of the lattice parameters. We then approximate the temperature dependence of the phonon frequencies, by calculating the eigenmodes of the dynamical matrix at the a, c lattice parameters for the corresponding temperature.…”

Section: Effect Of Change In Lattice Parameters On the Phonon Modesupporting

confidence: 75%

“…To motivate such measurements, we suggest that ErMnO 3 might show intriguing deviations from the temperature evolution that we calculated within Landau theory since it will likely have at least partial order-disorder character, in which the high-temperature structure is locally distorted, but the distortion vanishes on average. Such orderdisorder behavior was recently identified in the related material YMnO 3 [42], where inelastic neutron scattering indicated only limited phonon softening [60][61][62]. We suggest that ErMnO 3 is a good candidate for detection of the predicted emergence of a central peak at the transition (see for example [63]), which has so far proved elusive.…”

Section: Discussionsupporting

confidence: 60%

“…This mode has shown to be irrelevant in the region of the phase transition [40], a concept referred to as dangerous irrelevance [41]. The recent demonstration that the hexagonal manganites disorder continuously on all length scales close to T c [42] reinforces the continuous U(1) behavior in the region of the phase transition.…”

Section: B Structural Phase Transition In the Hexagonal Manganitesmentioning

confidence: 98%

“…Perturbations of the amplitude conserve the spacegroup symmetry, thus they belong to the irreducible representation A1. Perturbations of the order-parameter angle change the space-group symmetry from the ferroelectric P6 3 cm to P3c1, which corresponds to the irreducible representation B1 [42].…”

Section: B Structural Phase Transition In the Hexagonal Manganitesmentioning

confidence: 99%

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Manifestation of structural Higgs and Goldstone modes in the hexagonal manganites

et al. 2020

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Structural phase transitions described by Mexican hat potentials should in principle exhibit aspects of Higgs and Goldstone physics. Here, we investigate the relationship between the phonons that soften at such structural phase transitions and the Higgs-and Goldstone-boson analogs associated with the crystallographic Mexican hat potential. We show that, with the exception of systems containing only one atom type, the usual Higgs and Goldstone modes are represented by a combination of several phonon modes, with the lowestenergy phonons of the relevant symmetry having substantial contribution. Taking the hexagonal manganites as a model system, we identify these modes using Landau theory, and predict the temperature dependence of their frequencies using parameters obtained from density functional theory. Separately, we calculate the additional temperature dependence of all phonon mode frequencies arising from thermal expansion within the quasiharmonic approximation. We predict that Higgs-mode softening will dominate the low-frequency vibrational spectrum of InMnO 3 between zero Kelvin and room temperature, whereas the behavior of ErMnO 3 will be dominated by lattice expansion effects. We present temperature-dependent Raman scattering data that support our predictions, in particular confirming the existence of the Higgs mode in InMnO 3 .

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Electric field control of magnetism: multiferroics and magnetoelectrics

Ramesh

Martin

2021

Riv. Nuovo Cim.

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This article is written on behalf of a large number of colleagues, collaborators, and researchers in the field of complex oxides as well as current and former students and postdocs who continue to enable and undertake cutting-edge research in the field of multiferroics, magnetoelectrics, and the pursuit of electric-field control of magnetism. What we present is something that is extremely exciting from both a fundamental science and applications perspective and has the potential to revolutionize our world. Needless to say, to realize this potential will require numerous new innovations, both in the fundamental science arena as well as translating these scientific discoveries into real applications. Thus, this article will attempt to bridge the gap between fundamental condensed-matter physics and the actual manifestations of the physical concepts into real-life applications. We hope this article will help spur more translational research within the broad materials physics community. KeywordsMultiferroics • magnetoelectric coupling • Thin films • spin-coupling • Electric field control of magnetism

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

Cited by 44 publications

References 72 publications

A Monte-Carlo Study on the Coupling of Magnetism and Ferroelectricity in the Hexagonal Multiferroic RMnO3

A Monte-Carlo Study on the Coupling of Magnetism and Ferroelectricity in the Hexagonal Multiferroic RMnO3

Manifestation of structural Higgs and Goldstone modes in the hexagonal manganites

Electric field control of magnetism: multiferroics and magnetoelectrics

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