Symmetry Guide to Ferroaxial Transitions

Hlinka, J.; Přívratská, Jana; Ondrejkovic, P.; Janovec, V.

doi:10.1103/physrevlett.116.177602

Cited by 93 publications

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“…Under the space-time inversion group, two-types of multipoles are often discussed, namely, electric multipole (E: polar/true tensor) and magnetic multipole (M: axial/pseudo tensor) 1,2, 18 . In addition to these ordinary multipoles, another two-types of multipoles are definable: one is the electric toroidal (ET) multipole and the other is the magnetic toroidal (MT) multipole, which have opposite parity from the ordinary ones under spatial inversion [19][20][21][22] . The most familiar toroidal multipole is the MT dipole.…”

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Microscopic Description of Electric and Magnetic Toroidal Multipoles in Hybrid Orbitals

Hayami

Kusunose

2018

J. Phys. Soc. Jpn.

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We present a general formalism of multipole descriptions under the space-time inversion group. We elucidate that two types of atomic toroidal multipoles, i.e., electric and magnetic, are fundamental pieces to express electronic order parameters in addition to ordinary electric and magnetic multipoles. By deriving quantummechanical operators for both toroidal multipoles, we show that electric (magnetic) toroidal multipole higher than dipole (monopole) can become a primary order parameter in a hybridized-orbital system. We also demonstrate emergent cross-correlated couplings between electric, magnetic, and elastic degrees of freedom, such as magneto-electric and magneto(electro)-elastic couplings, under toroidal multipole orders.

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Microscopic Description of Electric and Magnetic Toroidal Multipoles in Hybrid Orbitals

Hayami

Kusunose

2018

J. Phys. Soc. Jpn.

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“…172 of Ref. [9]) implies the existence of four ferroelastic and ferroelectric domain states, most work has been done in the cubic phase, where the domains do not intervene.…”

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Lattice modes and the Jahn-Teller ferroelectric transition ofGaV4S8

et al. 2016

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Crystal of GaV 4 S 8 , a multiferroic system hosting a Néel-type skyrmion lattice phase, has been investigated by polarized Raman and IR spectroscopy above and below the ferroelectric phase transition. Counts of the observed IR and Raman-active modes belonging to distinct irreducible representations agree quite well with group-theory predictions. Phonon spectra are assigned and interpreted with the aid of ab initio calculations of the phonon spectra in the ferroelectric phase. Results allow appreciation of phonon frequencies of the modes involved in Jahn-Teller distortion and their contribution to the spontaneous polarization. DOI: 10.1103/PhysRevB.94.060104 The ternary chalcogenide GaV 4 S 8 (GVS) has recently attracted considerable attention due to its multiferroic properties. First of all, the low-temperature zero-field phase of GVS is simultaneously ferroelectric and ferromagnetic up to about T FM ≈ 5 K. Its magnetization corresponds to S = 1/2 per formula unit and its electric polarization is also appreciable (P s ≈ 1 μC cm −2 ). Moreover, clear experimental evidence has been found for a sizable magnetoelectric coupling [1]. Secondly, GVS exhibits an interesting magnetic cycloidal order between T FM and T N = 13 K, which can be transformed by a moderate magnetic field (of about 40 mT) into a Néel-type skyrmion lattice (SkL) phase [2]. As predicted in the seminal works of Bogdanov et al. [3][4][5] the important prerequisite for the appearance of this very unusual spin texture (Néel-type SkL) is the polar macroscopic symmetry of the underlying crystal lattice. In GVS, the suitable C 3v symmetry emerges together with the ferroelectric polarization below the JahnTeller phase transition T JT = 42 K [6,7]. This unusual phase transition was shown to be driven by a strong electron-phonon coupling between the unpaired electron in the highest-energy, orbitally degenerate electronic state of the V 4 cluster and two corresponding Jahn-Teller-active zone-center modes of the noncentrosymmetric paraelectric structure of GVS [8].The aim of this Rapid Communication is to explore the role of the zone-center phonon modes in the phase transition using Raman and IR spectroscopy and the ab initio approach. In particular, we have (i) determined the spectrum of zonecenter phonon modes of GVS, (ii) identified two phonon modes primarily involved in the phase transition, and (iii) related these findings to the Jahn-Teller phase transition and dielectric properties of GVS.GVS is a lacunar spinel, i.e., it can be presented as a spinel structure lacking every second Ga atom. It can be viewed as a face-centered cubic (fcc) lattice formed of * hlinka@fzu.cz tetrahedral GaS 4 and cubane V 4 S 4 clusters [see Fig. 1(a)]. The paraelectric phase of GaV 4 S 8 has a noncentrosymmetric cubic (T d ) symmetry [6]. The hybridization of the valence states of the vanadium metal ions within the V 4 S 4 magnetic building blocks leads to one unpaired localized electron occupying a triply degenerate t 2 cluster orbital with an overall spin 1/2. The Ga...

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“…phase transition (through the common structural motif between both structural modifications). The enriched diversity of LiO 4 and SO 4 tetrahedrabased phases, built by chains, layers or three-dimensional connections, can serve for studies of the macroscopic symmetry lowering or/and changes in the [LiSO 4 ] À framework dimensionality and their current applications, for instance, ferroic phases, nonlinear and transport properties (Hlinka et al, 2016;Mishra et al, 2013).…”

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“…Below 285 K, it undergoes a ferroelectric-ferroelastic phase transition with a final monoclinic phase (P2 1 =c; Mashiyama & Kasano, 1993). Very recently, this non-polar and ferroelastic phase has been identified as a ferroaxial crystal structure (Hlinka et al, 2016). There is also the so-called -LiNH 4 SO 4 (-LAS) or -modification.…”

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Structures and thermal stability of the α-LiNH₄SO₄ polytypes doped with Er³⁺ and Yb³⁺

Sabalisck

Guzmán-Afonso

González-Silgo

et al. 2017

Acta Crystallogr Sect B

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In order to clarify the polymorphism in the lithium sulfate family, LiRE x (NH 4 ) 1 À x SO 4 (0.5 x 4.0 mol%, nominal value; RE = Er 3+, Yb 3+and Dy 3+ ) crystals were grown from aqueous solution by slow evaporation between 298 and 313 K. The doping of the samples allowed us to obtain two polymorphic forms, and , of LiNH 4 SO 4 (LAS). By means of X-ray diffraction (XRD) in single crystals, we determined the crystal structures of two newpolytypes, which we have named 1 -and 2 -LAS. They present the same space group P2 1 /c and the following relation among their lattice parameters: a 2 = Àc 1 , b 2 = Àb 1 , c 2 = À2a 1 À c 1 . In order to evaluate the stability of the newpolytypes, we performed thermal analysis, X-ray diffraction and dielectric spectroscopy on single crystals and polycrystalline samples over the cyclic temperature range: 190 ! 575 ! 190 K. The results obtained by all the techniques used in this study demonstrate that -polytypes are stable across a wide range of temperatures and they show an irreversible phase transition to the paraelectric -phase above 500 K. In addition, a comparative study of -andpolytypes shows that both polymorphic structures have a common axis, with a possible intergrowth that facilitates their coexistence and promotes the reconstructive ! transition. This intergrowth was related to small anomalies detected between 240 and 260 K, in crystals with an -habit.

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Symmetry Guide to Ferroaxial Transitions

Cited by 93 publications

References 40 publications

Microscopic Description of Electric and Magnetic Toroidal Multipoles in Hybrid Orbitals

Microscopic Description of Electric and Magnetic Toroidal Multipoles in Hybrid Orbitals

Lattice modes and the Jahn-Teller ferroelectric transition ofGaV4S8

Structures and thermal stability of the α-LiNH₄SO₄ polytypes doped with Er³⁺ and Yb³⁺

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Symmetry Guide to Ferroaxial Transitions

Cited by 93 publications

References 40 publications

Microscopic Description of Electric and Magnetic Toroidal Multipoles in Hybrid Orbitals

Microscopic Description of Electric and Magnetic Toroidal Multipoles in Hybrid Orbitals

Lattice modes and the Jahn-Teller ferroelectric transition ofGaV4S8

Structures and thermal stability of the α-LiNH4SO4 polytypes doped with Er3+ and Yb3+

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Structures and thermal stability of the α-LiNH₄SO₄ polytypes doped with Er³⁺ and Yb³⁺