Experimental evidence for an intermediate phase in the multiferroic YMnO3

We have studied YMnO$_{3}$ by high-temperature synchrotron X-ray powder diffraction, and have carried out differential thermal analysis and dilatometry on a single crystal sample. These experiments show two phase transitions at about 1100K and 1350K, respectively. This demonstrates the existence of an intermediate phase between the room temperature ferroelectric and the high temperature centrosymmetric phase. This study identifies for the first time the different high-temperature phase transitions in YMnO$_{3}$.Comment: 10 pages 5 figures. New version, Additional data, Journal of Physics: Condensed Matter, in Pres

Phenomenological Landau analysis of predicted magnetoelectric fluorides: KMnFeF6_{6} and Ba2_{2}Ni7_{7}F18_{18}

Recently, we predicted based on symmetry considerations that KMnFeF$_{6}$ and Ba$_{2}$Ni$_{7}$F$_{18}$ are likely magnetoelectric multiferroic materials. In this contribution, we investigate with Landau theory and crystal structure considerations the polarization and the linear magnetoelectric effect in these materials. Based on these two examples, we show that any magnetoferroelectric will display additional electrical polarization below its magnetic ordering temperature. This additional electrical polarization is not related to the linear magnetoelectric effect. Its magnitude depends on the dielectric susceptibility.Comment: 11 pages, accepted for publication in Journal of Physics: Condensed Matte

Evolution de la perméabilité haute fréquence (jusqu'à 3GHz) de couches minces ferromagnétiques à base de cobalt en fonction de la contrainte

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