Electric Field Control of Terahertz Polarization in a Multiferroic Manganite with Electromagnons

Abstract

All-electrical control of a dynamic magnetoelectric effect is demonstrated in a classical multiferroic manganite DyMnO3, a material containing coupled antiferromagnetic and ferroelectric orders. Due to intrinsic magnetoelectric coupling with electromagnons a linearly polarized terahertz light rotates upon passing through the sample. The amplitude and the direction of the polarization rotation are defined by the orientation of ferroelectric domains and can be switched by static voltage. These experiments allow the terahertz polarization to be tuned using the dynamic magnetoelectric effect.PACS numbers: 75.85.+t, 78.20.Jq, 78.20.Ek, 75.30.Ds Electric and magnetic field control of the propagation and the polarization state of terahertz radiation is one of the prerequisites for continuous progress of modern electronics. A number of recent developments in this direction have been achieved using multiferroics, i.e. materials simultaneously revealing electric and magnetic ordering [1][2][3][4][5]. Several multiferroics provide not only a direct coupling between static electric and magnetic properties but also give a possibility to modify dynamic susceptibilities by external fields. Application of a static magnetic field to the multiferroic materials leads to dichroism in the terahertz range [6,7] or even to more complex effects like controlled chirality [8] or directional dichroism [9][10][11]. Electric control of terahertz radiation is more difficult to realize and it has been recently demonstrated in Raman scattering experiments [12].Dynamical properties of several multiferroic materials in the terahertz range are governed by novel magnetoelectric modes called electromagnons [13][14][15][16]. Electromagnons may be defined as collective excitations of the magnetic structure which are coupled to the electric dipole moment.They may be regarded as a mixture of magnons and phonons. In orthorhombic rare earth manganites RMnO 3 one generally observes several electromagnons in the terahertz and sub-terahertz range. A strong high frequency mode around 2-3 THz is well understood on the basis of a symmetric Heisenberg exchange (HE) coupling [17,18] as a zone edge magnon which can be excited by electric component of the electromagnetic radiation. A second intensive mode existing at 0.5-1 THz has been explained using the same mechanism but including a Brillouin zone folding due to modulation of the magnetic cycloid [18,19]. In the sub-terahertz frequency range a series of weaker modes is observed in optical [14,20] and neutron scattering experiments [21]. These modes are explained as the magnetic eigenmodes of the spin cycloid in RMnO 3 . Some of these modes may get an electrical dipole activity due to the relativistic Dzyaloshinskii-Moriya (DM) mechanism. Dynamic contributions due to this mechanism have been investigated both experimentally and theoretically [20,[22][23][24][25]. In spite of its weakness, the DM interaction is a promising mechanism especially in application to spiral magnets as it connects static spontaneous ...

Influence of nonmagnetic Zn substitution on the lattice and magnetoelectric dynamical properties of the multiferroic material CuO

“…This mode was previously found [54] to lower in energy for isotopically pure 65 CuO in comparison to 63 CuO, demonstrating that it results from an LA motion of Cu 2+ ions along (101), modulating the strongest superexchange interaction J 80 meV [31]. The three principal Raman modes were at the same energies for 65 CuO and 63 CuO, as expected for vibrations associated only with oxygen motion [54], while they shifted to lower frequencies for Cu 18 O than for Cu 16 O [59]. Further evidence for the magnetically induced zone folding of phonons in CuO was reported by Kuz'menko et al, who reported additional IR-active modes that were linked to phonon modes at the X and A points [51].…”

“…Electromagnons-spin waves that become electric-dipole active in a magnetoelectric phase-are a recently discovered quasiparticle excitation that provide a window into the important spin interactions of magnetoelectrics [11][12][13][14][15][16][17]. The electric-field tuning of electromagnons in DyMnO 3 , an improper ferroelectric multiferroic [18], and of magnons in bulk BiFeO 3 , a proper ferroelectric multi-* j.lloyd-hughes@warwick.ac.uk ferroic [19], establish the potential of spin waves in data processing and communications [20].…”

“…A DM electromagnon has been reported in TbMnO 3 , substantially weaker than the Heisenberg electromagnons [16]. The electric-field control of polarization of terahertz (THz) radiation has recently been demonstrated using DM electromagnons in DyMnO 3 [18].…”

Structural and spectroscopic properties of the polar antiferromagnet Ni2MnTeO6

“…For example, directional dichroism might reveal the character of the spin excitation observed in the THz spectra and identify whether it corresponds to a pure magnon or electromagnon, as in Ni 3 TeO 6 . Unfortunately, since the magnetic excitation lies below 8 cm -1 , more precise transmission measurements with a spectrometer based on backward-wave oscillator sources 39 and a crystal with diameter at least 10 mm would be required. In addition, using single crystals, one can avoid possible impurities often present at grain boundaries of polycrystalline samples, thus the anomaly seen at 23 K could be absent or better resolved.…”

Terahertz Electrodynamics in Transition Metal Oxides

“…[184] Pimenov et al observed the new collective excitation corresponding to this multiferroic state known as electromagnon, i.e., electric-dipole active magnetic excitation in the imaginary part of the THz dielectric constant for GdMnO 3 and TbMnO 3 . [184,[187][188][189] This electromagnon has been reported as the rotational mode of the spiral spin plane which showed the absorption mode for E ω perpendicular to the plane of the spiral spin order. Such studies were further carried out with enhanced precision.…”