Observation of electromagnons in multiferroic manganites

Magnetodielectric materials are characterized by a strong coupling of magnetic and dielectric properties and in rare cases simultaneously exhibit both, magnetic and polar order. Among other multiferroics, TbMnO3 and GdMnO3 reveal a strong magneto-dielectric (ME) coupling and as a consequence fundamentally new spin excitations exist: Electro-active magnons, or electromagnons, i. e. spin waves which can be excited by ac electric fields.
Here we show that these excitations appear in the phase with an incommensurate (IC) magnetic structure of the manganese spins. In external magnetic fields this IC structure can be suppressed and the electromagnons are wiped out, thereby inducing considerable changes in the index of refraction from dc up to THz frequencies. Hence, besides adding a new creature to the zoo of fundamental excitations, the refraction index can be tuned by moderate magnetic fields, which allows the design of a new generation of optical switches and optoelectronic devices.   electromagnons

Spectrum of electromagnon in GdMnO3. Frequency dependence of the imaginary part of the THz-dielectric function in GdMnO3 with e||a and B||c. Symbols: experimental data, solid line: model calculations adding an over-damped Lorentzian to the residual high-frequency contribution (dashed line).

To learn more, see: A. Pimenov, A. A. Mukhin, V. Yu. Ivanov, V. D. Travkin, A. M. Balbashov and A. Loidl, Possible evidence for electromagnons in multiferroic manganites, Nature Physics 2, 97-100 (2006), or (cond-mat/0602173)..