The low energy part of the vibration spectrum in PbMg 1/3 Nb 2/3 O 3 (PMN) relaxor ferroelectric has been studied by means of neutron scattering above and below the Burns temperature, T d . The transverse acoustic and the lowest transverse optic phonons are strongly coupled and we have obtained a model for this coupling. We observe that the lowest optic branch is always underdamped. A resolution-limited central peak and quasi-elastic scattering appear in the vicinity of the Burns temperature. It is shown that it is unlikely that the quasielastic scattering originates from the combined effects of coupling between TA and TO phonons with an increase of the damping of the TO phonon below T d . The quasi-elastic scattering has a peak as a function of temperature close to the peak in the dielectric constant while the intensity of the central peak scattering increases strongly below this temperature. These results are discussed in terms of a random field model for relaxors.
The state with a giant permittivity ͑Ј ϳ 10 4 ͒ and ferromagnetism have been observed above 185 K ͑including room temperature͒ in single crystals of diluted semiconductor manganite-multiferroic Eu 0.8 Ce 0.2 Mn 2 O 5 in the investigations of x-ray diffraction, heat capacity, dielectric and magnetic properties, conductivity, and Raman light-scattering spectra of this material. X-ray diffraction study has revealed a layered superstructure along the c axis at room temperature. A model of the state with a giant Ј including as-grown two-dimensional layers with doping impurities, charge carriers, and double-exchange-coupled Mn 3+-Mn 4+ ion pairs is suggested. At low temperatures these layers form isolated electrically neutral small-size one-dimensional superlattices, in which de Haas-van Alphen oscillations were observed. As temperature grows and hopping conductivity increases, the charge carrier self-organization in the crystal causes formation of a layered superstructure consisting of charged layers ͑with an excess Mn 3+ concentration͒ alternating with dielectric layers of the initial crystal-the ferroelectricity due to charge-ordering state. Ferromagnetism results from double exchange between Mn 3+ and Mn 4+ ions by means of charge carriers in the charged layers. Temperature evolution of frequency shifts of A g modes and quasielastic scattering in Raman-scattering spectra agree with the pattern of phase transitions in ECMO suggested.
Based on measurements of soft x-ray magnetic diffraction under in situ applied electric field, we report on significant manipulation and exciting of commensurate magnetic order in multiferroic ErMn2O5. The induced magnetic scattering intensity arises at the commensurate magnetic Bragg position whereas the initial magnetic signal almost persists. We demonstrate the possibility to imprint a magnetic response function in ErMn2O5 by applying an electric field.
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