Magnetochiral dichroism resonant with electromagnons in a helimagnet

Kibayashi, Shunsuke; Takahashi, Y.; Seki, Shu; Tokura, Y.

doi:10.1038/ncomms5583

Cited by 54 publications

(54 citation statements)

References 44 publications

(83 reference statements)

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“…The first one, the so-called magnetochiral dichroism (MChD), requires a chiral material with finite magnetization, and the directional dichroism is present for light beams propagating parallel and antiparallel to the direction of the magnetization. MChD has been detected in several akermanite compounds, [8,11] and in Cu(Fe,Ga)O 2 [12]. The second one is realized when a material simultaneously possesses magnetization, M and electric polarization (or a polar axis), P [19].…”

Section: Pacs Numbersmentioning

confidence: 99%

“…These functionalities rely on the magneto-electric (ME) effect which is enhanced in multiferroics by the coexistence of ferroelectric and magnetic order. Recent studies of multiferroic materials from gigahertz frequencies to Xray wavelengths have demonstrated that finite frequency ME effect gives rise to another useful phenomenon, the directional dichroism [4][5][6][7][8][9][10][11][12][13][14]. The non-reciprocal directional dichroism and its Kramers-Kronig counterpart, non-reciprocal directional birefringence, are the absorption coefficient and refractive index differences, respectively, for counter-propagating light beams detectable irrespective of the light polarization state.…”

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Unidirectional terahertz light absorption in the pyroelectric ferrimagnetCaBaCo4O7

et al. 2015

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Spin excitations were studied by absorption spectroscopy in CaBaCo4O7 which is a type-I multiferroic compound with the largest magnetic-order induced ferroelectric polarization (∆P =17 mC/m 2 ) reported, so far. We observed two optical magnon branches: a solely electric dipole allowed one and a mixed magnetoelectric resonance. The entangled magnetization and polarization dynamics of the magnetoelectric resonance gives rise to unidirectional light absorption, i.e. that magnon mode absorbs the electromagnetic radiation for one propagation direction but not for the opposite direction. Our systematic study of the magnetic field and temperature dependence of magnon modes provides information about the energies and symmetries of spin excitations, which is required to develop a microscopic spin model of CaBaCo4O7. PACS numbers:Multiferroic materials have gained tremendous interest because of their versatile possibilities for applications in sensing, data storage and computing [1][2][3]. These functionalities rely on the magneto-electric (ME) effect which is enhanced in multiferroics by the coexistence of ferroelectric and magnetic order. Recent studies of multiferroic materials from gigahertz frequencies to Xray wavelengths have demonstrated that finite frequency ME effect gives rise to another useful phenomenon, the directional dichroism [4][5][6][7][8][9][10][11][12][13][14]. The non-reciprocal directional dichroism and its Kramers-Kronig counterpart, non-reciprocal directional birefringence, are the absorption coefficient and refractive index differences, respectively, for counter-propagating light beams detectable irrespective of the light polarization state. These effects enable new applications for multiferroics in photonics, e.g. one-way light guides and polarization rotators. The largest directional dichroism in multiferroics is at terahertz (THz) frequencies [11] what can boost terahertz photonics in the future, similar to the prospect of graphene non-reciprocal terahertz devices [15]. The dc and the finite frequency ME effect, which determine the efficiency of any multiferroic device, are intimately connected by a sum rule [16] allowing a large static ME effect only if a large non-reciprocal directional dichroism is present in the absorption spectrum of electromagnetic radiation. The pyroelectric ferrimagnet CaBaCo 4 O 7 is a type-I multiferroic compound with the largest magnetic-order induced ferroelectric polarization (∆P =17 mC/m 2 ) reported, so far [17]. In this paper we report a magnon mode in CaBaCo 4 O 7 which shows unidirectional light absorption. Namely, the non-reciprocal directional dichroism is so strong for the magnon resonance that it absorbs terahertz radiation only in one direction, but not in the opposite direction.In the long wavelength limit the directional dichroism emerges from the dynamic magnetoelectric (ME) coupling, δP ω =χ em (ω)H ω and δM ω =χ me E ω [7,8]. The induced polarization, δP ω and magnetization, δM ω interfere constructively/destructively with H ω and E ω fields of the l...

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Section: Pacs Numbersmentioning

confidence: 99%

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confidence: 99%

Unidirectional terahertz light absorption in the pyroelectric ferrimagnetCaBaCo4O7

et al. 2015

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“…Indeed observations of the directional dichroism have been reported for several multiferroic materials such as Ba 2 CoGe 2 O 7 [17][18][19], RMnO 3 (R =rare-earth ions) [20,21], and CuFe 1−x Ga x O 2 [22], in which nontrivial spin orders induce the ferroelectric polarization via the relativistic spin-orbit interaction. In these materials, the optical ME effect is observed at the electromagnon resonance frequencies in the terahertz (THz) regime.…”

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Microwave Magnetochiral Effect inCu2OSeO3

Mochizuki

2015

Phys. Rev. Lett.

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We theoretically find that in a multiferroic chiral magnet Cu2OSeO3, resonant magnetic excitations are coupled to collective oscillation of electric polarization, and thereby attain simultaneous activity to ac magnetic field and ac electric field. Because of interference between these magnetic and electric activation processes, this material hosts gigantic magnetochiral dichroism on microwaves, that is, the directional dichroism at gigahertz frequencies in Faraday geometry. The absorption intensity of microwave differs by as much as ∼30% depending on whether its propagation direction is parallel or antiparallel to the external magnetic field.PACS numbers: 76.50.+g,78.20.Ls,78.20.Bh,78.70.Gq Collective excitations of spins in magnets, so-called magnons or spin waves, can be activated not only via a direct process with ac magnetic field H ω coupled to magnetizations but also via an electric excitation by ac electric field E ω coupled to charge degrees of freedom. When the magnon or spin-wave modes have simultaneous activity to the H ω and E ω components of electromagnetic waves, interference between the two activation processes, that is, the magnetically activating and the electrically activating processes, gives rise to peculiar optical and/or microwave phenomena, so-called optical ME effect. One of the most important examples is the directional dichroism, that is, oppositely propagating electromagnetic waves exhibit different absorptions.Multiferroic materials with concurrent magnetic and ferroelectric orders [1][2][3][4][5][6][7][8] provide an opportunity to realize the electric-dipole active magnons (so-called electromagnons) [9][10][11][12][13], and thus the optical ME effect via the magnetoelectric coupling [14][15][16]. Indeed observations of the directional dichroism have been reported for several multiferroic materials such as Ba 2 CoGe 2 O 7 [17][18][19], RMnO 3 (R =rare-earth ions) [20,21], and CuFe 1−x Ga x O 2 [22], in which nontrivial spin orders induce the ferroelectric polarization via the relativistic spin-orbit interaction. In these materials, the optical ME effect is observed at the electromagnon resonance frequencies in the terahertz (THz) regime.The directional dichroism is observed also at higher frequencies, i.e., x-ray and visible-light regimes in several polar magnets, which is caused by electron transitions among the spin-orbit multiplets [23][24][25][26][27][28][29]. However, observations of the effect at gigahertz (GHz) frequencies are quite limited and the effect observed so far is very tiny whose difference in absorption intensity is only 2.5% at most [32], while the directional dichroism at GHz frequencies is anticipated for application to microwave devices [30]. This is because most of the well-known multiferroic materials based on simple spiral or antiferromagnetic spin structures with short-period modulation tend to have relatively large spin-wave gaps of several meV, which inevitably results in rather high resonance frequencies in THz regime. To achieve the microwave ME effect...

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“…The presence of an external magnetic field within a chiral medium introduces time-reversal as well as space-reversal symmetry breaking simultaneously, and, as a second-order phenomenon, it is very hard to measure experimentally. So far, magnetochirality has been verified in liquid molecular systems, organic compounds, anisotropic crystals and chiral ferromagnets [2][3][4][5][6][7][8][9][10][11][12][13][14]. Recently, it has been theoretically proposed that magnetochiral dichroism (MChD) can be promoted in chiral magnetic metamaterials such as helical lattices of magnetic garnet spheres [15].…”

Section: Introductionmentioning

confidence: 99%

Magnetochirality in hierarchical magnetoplasmonic clusters

Yannopapas

2015

Solid State Communications

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Magnetochiral dichroism resonant with electromagnons in a helimagnet

Cited by 54 publications

References 44 publications

Unidirectional terahertz light absorption in the pyroelectric ferrimagnetCaBaCo4O7

Unidirectional terahertz light absorption in the pyroelectric ferrimagnetCaBaCo4O7

Microwave Magnetochiral Effect inCu2OSeO3

Magnetochirality in hierarchical magnetoplasmonic clusters

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