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...

The authors introduce an emergent method to fabricate a few-nanometer-size columnar superlattice with a checkerboard pattern in inorganic spinels by harnessing the Jahn-Teller structural distortion. Transmission electron microscope images reveal that the fundamental building blocks are two types of long nanorods with the ∼4×4×70nm3 size, which are alternatively stacked in a way that the cross sectional and side views show checkerboard and herringbone patterns, respectively. The authors discuss that the strain induced by the Jahn-Teller distortion causes this peculiar self-assembled nanostructure in the coherent mixture of two spinel phases. This pure solid state self-assembly can be implemented to fabricate heterogeneous nanostructures with practical functionalities.