Electromagnons in multiferroic manganites

Rolando Aguilar, Physics Department, U of Maryland

In multiferroic materials the coexistence of magnetic and ferroelectric orders can produce cross coupling between electric and magnetic signals that are usually independent and exhibit interesting new fundamental features. The absence of both time and space inversion symmetry in relatively low symmetry crystal structures can produce a rich array of novel magneto-electric phenomena. One such new phenomenon, which is the topic of this talk, is a strong coupling between the low lying magnetic and lattice excitations to produce spin waves that interact strongly with light by acquiring electric dipole activity from the phonons. Therefore these excitations, called electromagnons, produce a contribution to the static dielectric constant that can be manipulated by magnetic fields. I will discuss the electromagnon excitations in 2 classes of multiferroic materials, RMn2O5 and RMnO3, where R is a rare earth ion or Y. The origin of these excitations will be discussed in terms of the symmetric Heisenberg exchange interaction, as opposed to the antisymmetric Dzyaloshinskii-Moriya exchange that has traditionally been used to explain the static ferroelectric polarization. A model of symmetric exchange striction is used for both families of materials that is capable of reproducing the main observed features of the electromagnons as measured by their interaction with light. *Work done in collaboration with A.B. Sushkov, M. Mostovoy, S-W. Cheong and H.D. Drew. Support from NSF-MRSEC DMR-0520471 is acknowledged.

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