Magnetic excitations in a cycloidal magnet: the magnon spectrum of multiferroic TbMnO<sub>3</sub>

Senff, D.; Aliouane, N.; Argyriou, D. N.; Hiess, A.; Regnault, L.P.; Link, P.; Hradil, K.; Sidis, Y.; Braden, M.

doi:10.1088/0953-8984/20/43/434212

Cited by 58 publications

(101 citation statements)

References 50 publications

(130 reference statements)

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“…Its maximum is located around the electromagnon frequency and its total spectral weight for all reasonable parameters of the model is less than 10% of the spectral weight of the singlemagnon peak. This shows that the peak at 60 cm −1 results from the photoexcitation of a single zone boundary magnon, which can be identified in the magnon spectra obtained by inelastic neutron scattering [21]. Even though charged magnons can also be excited by e c and e b through couplings similar to Eq.…”

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confidence: 68%

Origin of Electromagnon Excitations in MultiferroicRMnO3

et al. 2009

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Electromagnon excitations in multiferroic orthorhombic RMnO3 are shown to result from the Heisenberg coupling between spins despite the fact that the static polarization arises from the much weaker Dzyaloshinskii-Moriya (DM) exchange interaction. We present a model incorporating the structural characteristics of this family of manganites that is confirmed by far infrared transmission data as a function of temperature and magnetic field and inelastic neutron scattering results. A deep connection is found between the magnetoelectric dynamics of the spiral phase and the static magnetoelectric coupling in the collinear E-phase of this family of manganites. PACS numbers:The coupling between the magnetic and ferroelectric order in a diverse set of materials termed multiferroics is currently a topic of intense study [1,2]. The interplay between these two orders is particularly striking in materials where ferroelectricity appears as a consequence of spontaneously breaking of inversion symmetry of the magnetic ordering. In many such magnetic ferroelectrics the spins order in an incommensurate cycloidal spiral state [3]. The microscopic origin of ferroelectricity for this case has been discussed by a number of authors [4,5,6], leading to a consensus, generically termed the spiral mechanism. It relies on the lowering of the energy of the antisymmetric Dzyaloshinskii-Moriya (DM) exchange in the spiral state by a polar lattice distortion, which induces an electric polarization, P ∝ Q×R, where R ∝ S i ×S i+1 is the spin rotation axis, and Q is the wave vector of the spiral. These ideas have been of central importance in the recent discovery of new multiferroic compounds.Another apparent consequence of multiferroicity is the existence of novel coupled magnon-phonon excitations called electromagnons [7,8]. A magnon that gives rise to oscillations of electric polarization can be excited by electric fields, thereby coupling much more strongly to light than the usual magnetic dipole excitation of magnons corresponding to antiferromagnetic resonance (AFMR). The resulting electric dipole spectral weight has been transferred from the phonons down to the magnon frequency. The dynamic magnetoelectric effects resulting from the coupling between spin and polarization waves were discussed theoretically at an early stage of the research on multiferroic materials [9]. More recently, Katsura, Balatsky and Nagaosa (KBN) noted that the magnetoelectric coupling of the spiral mechanism, also gives rise to an electromagnon [10]. When the spiral plane rotates around Q, so does the induced electric polarization, which couples this magnetic excitation to electric field e of a light wave normal to the spiral plane: e R. The first observation of the electromagnon peak for e a in TbMnO 3 with the bc-plane spiral spin ordering (Q b) seemed to confirm this selection rule [7]. However, recent measurements on other spiral multiferroics from the same family of materials, Eu 0.75 Y 0.25 MnO 3 [11] and DyMnO 3 [12], showed that this selection rule is violated...

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confidence: 68%

Origin of Electromagnon Excitations in MultiferroicRMnO3

et al. 2009

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“…Experimentally this is related to a shift in the scattering wavevector to larger values for increasing the temperature above this phase transition. The lack of a large change in scattering wavevector upon excitation with 1.55 eV light suggests that under these conditions, propagation of changes in the long-range ordering of the spin system within a single domain is very slow; indeed the magnon dispersion indicates an exceedingly low group velocity for all relevant wavevectors [5,6]. Thus even if the spin system is very quickly disrupted at the sample surface, it would necessarily take a long time to propagate this perturbation into the bulk.…”

Section: Discussionmentioning

confidence: 99%

“…One of these derivatives, TbMnO3, exhibits multiferroicity below 27 K [2], and serves as a prototypical example of chiral spin order. The nature of the long range spin-cycloid ordering under equilibrium conditions has been studied and clarified using both neutron scattering [3][4][5][6] and resonant x-ray diffraction [7][8][9]. In the latter technique, soft X-rays tuned to the Mn L2 edge at 652 eV show a strong resonant enhancement giving direct information about the long-range spin order.…”

Section: Introductionmentioning

confidence: 99%

Magnetic order dynamics in optically excited multiferroicTbMnO3

Johnson¹,

Kubacka²,

Hoffmann³

et al. 2015

Phys. Rev. B

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We performed ultrafast time-resolved near-infrared pump, resonant soft X-ray diffraction probe measurements to investigate the coupling between the photoexcited electronic system and the spin cycloid magnetic order in multiferroic TbMnO3 at low temperatures. We observe melting of the long range antiferromagnetic order at low excitation fluences with a decay time constant of 22.3 ± 1.1 ps, which is much slower than the ~1 ps melting times previously observed in other systems. To explain the data we propose a simple model of the melting process where the pump laser pulse directly excites the electronic system, which then leads to an increase in the effective temperature of the spin system via a slower relaxation mechanism. Despite this apparent increase in the effective spin temperature, we do not observe changes in the wavevector q of the antiferromagnetic spin order that would typically correlate with an increase in temperature under equilibrium conditions. We suggest that this behavior results from the extremely low magnon group velocity that hinders a change in the spin-spiral wavevector on these time scales.2

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“…The up-to-date situation with the lowfrequency electromagnon is a bit more complicated. According to recent experimental results [24,25] on the closely similar multiferroic TbMnO 3 , the low-frequency electromagnon corresponds to an eigenmode of the cycloidal spin structure [26] which becomes infrared active due to an incommensurate spin modulation of the cycloid. We note that an alternative explanation based on anisotropic effects has been suggested as well [27,28].…”

Section: Introductionmentioning

confidence: 95%

Soft-mode behavior of electromagnons in multiferroic manganite

et al. 2010

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The behavior of the low-frequency electromagnon in multiferroic DyMnO3 has been investigated in external magnetic fields and in a magnetically ordered state. Significant softening of the electromagnon frequency is observed for external magnetic fields parallel to the a-axis (B a), revealing a number of similarities to a classical soft mode behavior known for ferroelectric phase transitions. The softening of the electromagnon yields an increase of the static dielectric permittivity which follows a similar dependence as predicted by the Lyddane-Sachs-Teller relation. Within the geometry B b the increase of the electromagnon intensity does not correspond to the softening of the eigenfrequency. In this case the increase of the static dielectric permittivity seem to be governed by the motion of the domain walls.

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Magnetic excitations in a cycloidal magnet: the magnon spectrum of multiferroic TbMnO₃

Cited by 58 publications

References 50 publications

Origin of Electromagnon Excitations in MultiferroicRMnO3

Origin of Electromagnon Excitations in MultiferroicRMnO3

Magnetic order dynamics in optically excited multiferroicTbMnO3

Soft-mode behavior of electromagnons in multiferroic manganite

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Magnetic excitations in a cycloidal magnet: the magnon spectrum of multiferroic TbMnO3

Cited by 58 publications

References 50 publications

Origin of Electromagnon Excitations in MultiferroicRMnO3

Origin of Electromagnon Excitations in MultiferroicRMnO3

Magnetic order dynamics in optically excited multiferroicTbMnO3

Soft-mode behavior of electromagnons in multiferroic manganite

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Magnetic excitations in a cycloidal magnet: the magnon spectrum of multiferroic TbMnO₃