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Accueil > Evénements > Séminaires > Archives 2011 > Electromagnons in multife
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Séminaire général

Electromagnons in multiferroics : from observations to applications

Maximilien Cazayous

Magnetoelectric multiferroics possess coexisting magnetic and ferroelectric phases, with cross-correlation effects between magnetic and electrical degrees of freedom. As such, they can potentially be used to control spin-based properties by electric fields, with very low associated power dissipation. Indeed, just as coupling between magnetic and ferroelectric order parameters exists in multiferroics, coupled spin and lattice excitations termed electromagnons have also been demonstrated. Such mixed excitations have been evidenced at low temperature in multiferroic manganites (TbMnO3, ..) and suspected at room temperature in BiFeO3. Such novel excitations are directly related to electromagnetic coupling and reflect the intimate relationship between magnetic and ferroelectric magnetic orders. However, the exact magnetic and the polar components of the electromagnons has not been yet identified. Electromagnons probably belong to the most challenging open questions in the field and are currently under intense investigation

After an introduction to multiferroic materials and the concept of electromagnon, I show that in multiferroic TbMnO3 a c-axis magnetic field strongly impact the electromagnons excitations. [1] The electrical polarization of the electromagnons is strongly altered under magnetic field whereas their magnetic part is preserved. Entering the paraelectric phase the spectral weight of the electromagnons is transferred to the magnon excitations. The magnetic excitation and the polar activity at the origin of the electromagnons are discussed under the light of Heisenberg simulations.

In the second part of the talk, I show that in multiferroic BiFeO3 spin wave excitations can be controlled by an electric field at room-temperature, low power and in a non-volatile way. [2] Our experimental results clearly demonstrate that the frequency of spin waves can be varied by more than 30%, which represents a tunability several orders of magnitude larger than previously reported. We find that the ferroelectric polarisation acts as a handle to manage this tuning and demonstrate through Landau theory calculations that it originates from an electric-field-driven linear magnetoelectric coupling mechanism. Our results not only qualify BiFeO3 as a promising medium for magnonic devices but also, and more generally, extend the potential of this multifunctional material to transform information from one state variable into another (e.g., charge, spin, light, etc) in future hybrid computational architectures. We anticipate that they will inspire novel concepts in magnonics and encourage further exploration of coupled phenomena in multiferroics and other oxide-based systems.

[1] Magnetic field induced dehybridization of the electromagnons in multiferroic TbMnO3, P. Rovillain, M. Cazayous, Y. Gallais, A. Sacuto, M-A. Measson, H. Sakata and M. Mochizuki, Phys. Rev. Lett. 107, 027202 (2011).

[2] Electric-field control of spin waves at room temperature in multiferroic BiFeO3, P. Rovillain, R. de Sousa, Y. Gallais, A. Sacuto, M. A. Méasson, D. Colson, A. Forget, M. Bibes, A. Barthélémy, M. Cazayous, Nature Materials 9, 975 (2010).