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Séminaire MCMF

The Far Infrared Dynamics of Multiferriocs RMnO3 and RMn2O5 (R=Rare Earth)

Néstor E. Massa

Laboratorio Nacional de Investigación y Servicios en Espectroscopía Optica-Centro CEQUINOR, Universidad Nacional de La Plata, C. C. 962, 1900 La Plata, Argentina.

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In this talk we will cover experimental work carried out in perovskite and perovskite related multiferroics. These are materials where in a certain temperature range ferroelectric and magnetic orders coexist, i.e., they have two order parameters, spontaneous polarization (antiferroelectric, ferroelectric, ferrilectric), and spontaneous magnetization (antiferromagnetism, ferromagnetism, ferrimagnetism) triggering, by magnetoelectric coupling, one order by the other. I will report on the temperature dependent lattice dynamics of orthorhombic NdMnO3 from 4 K to dissociation by combining far infrared emissivity and reflectivity techniques. We prompt by oxidation small polaron and hopping conductivity at high temperatures denoting eg electrons mobility in a Jahn-Teller distorted environment. In the far infrared a phase like-mode becomes well defined at 300 K and condenses below TN into two hardening modes. Measurements in hexagonal TmMnO3 yield a similar picture but showing split in the phonon-like band due to lower symmetry and two superexchange interactions in the ab plane. We have also found that “spin-like” bands depend on the Rare Earth mass. We will then review our results for the impurity phases RMn2O5 (R=Rare Earth). Far infrared spectra of these compounds suggest that in spite of the increment in complexity both sets of compounds, RMnO3 and RMn2O5, share multiferroicity within a common framework lacking of strong structural rearrangements.

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