Low Symmetry Phase in (001) BiFeO3_3 Epitaxial Constrained Thin Films

The lattice of (001)-oriented BiFeO$_3$ epitaxial thin film has been identified by synchrotron x-ray diffraction. By choosing proper scattering zones containing the fixed (001) reflection, we have shown that low-symmetry phases similar to a $M_A$ phase exist in the thin film at room temperature. These results demonstrate a change in phase stability from rhombohedral in bulk single crystals, to a modified monoclinic structure in epitaxial thin films

Electromagnon excitations in modulated multiferroics

The phenomenological theory of ferroelectricity in spiral magnets presented in [M. Mostovoy, Phys. Rev. Lett. 96, 067601 (2006)] is generalized to describe consistently states with both uniform and modulated-in-space ferroelectric polarizations. A key point in this description is the symmetric part of the magnetoelectric coupling since, although being irrelevant for the uniform component, it plays an essential role for the non-uniform part of the polarization. We illustrate this importance in generic examples of modulated magnetic systems: longitudinal and transverse spin-density wave states and planar cycloidal phase. We show that even in the cases with no uniform ferroelectricity induced, polarization correlation functions follow to the soft magnetic behavior of the system due to the magnetoelectric effect. Our results can be easily generalized for more complicated types of magnetic ordering, and the applications may concern various natural and artificial systems in condensed matter physics (e.g., magnon properties could be extracted from dynamic dielectric response measurements).Comment: 5 page

PEROVSKITE TYPE SEIGNETTOMAGNETS

Nous avons donné une rapide revue des recherches expérimentales et théoriques de l'institut Karpov pour la synthèse et l'étude des ferromagnétiques de type perovskites.A short review of exprimental and theoretical investigations of Karpov Institute in the synthesis and study of perovskite type seignettomagnets has been given

Modulated charged defects and conduction behaviour in doped BiFeO 3 thin films

10.1088/0022-3727/42/16/162001Journal of Physics D: Applied Physics4216-JPAP

CRYSTAL STRUCTURE AND PROPERTIES OF NEW CADMIUMAND THALLIUM-CONTAINING PEROVSKITES

De nouveaux composés du type pervoskite à base de cadmium et de thallium ont été synthétisés. Une étude aux rayons X et des mesures de propriétés diélectriques ont été réalisées. Il a été possible de conclure qu'ils sont caractérisables par leur polarisation spontanée.New cadmium- and thallium-containing perovskites have been synthesized. A X-ray study and some dielectric measurements have been fulfilled. It has been concluded that a spontaneously-polarized characterizes their