Magnetically induced femtoscale strain modulations in HoMn2O5

International audienceX-ray scattering was used to investigate the magnetically induced ionic displacements in the low-temperature commensurate ferroelectric/antiferromagnetic phase of the multiferroic HoMn2O5. The structural modulation signal appearing at twice the magnetic wave vector km=(1/201/4) has been used, combined with symmetry analysis, to determine a model for the ionic displacements up to a precision of 10-3Å. The symmetry-breaking operations that are associated to the active irreducible representation have been experimentally determined from the analysis of the modulation modes. They reveal a lowering of symmetry to the polar point group m2m. Calculations based on the determined model show that the magnetic structure along the c direction is stabilized via nearest-neighbor and next-nearest-neighbor interactions through the rare-earth layer. We also show that by knowing both the magnetic and the magnetically induced strain waves patterns, it is possible to remove any phase ambiguity between the crystal and magnetic structures

Simultaneous dynamic electrical and structural measurements of functional materials

A new materials characterization system developed at the XMaS beamline, located at the European Synchrotron Radiation Facility in France, is presented. We show that this new capability allows to measure the atomic structural evolution (crystallography) of piezoelectric materials whilst simultaneously measuring the overall strain characteristics and electrical response to dynamically (ac) applied external stimuli

Order Parameters and Phase Diagrams of Multiferroics

The symmetry properties, order parameters, and magnetoelectric phase diagrams of multiferroics are discussed. After brief reviews of Ni$_3$V$_2$O$_8$, TbMnO$_3$, and RbFe(MoO$_4$)$_2$, we present a detailed analysis of RMn$_2$O$_5$ (with R=Y, Ho, Dy, Er, Tb, Tm).Comment: 23 pages, 7 figures, 3 tables. For FOCUS ON MULTIFERROICS (IOP

Intrinsic and extrinsic nature of the giant piezoelectric effect in the initial poling of PMN-PT

Demonstrating both the intrinsic and extrinsic nature of the giant piezoelectric effect (GPE) in complex solid solutions, near the morphotropic phase boundary, has been extremely challenging until now, because such materials exhibit multiple phases on the order of tens of microns across, meaning important information is lost due to averaging when using established high resolution diffraction techniques to extract three dimensional structural information. We have used a different approach proposed by Nisbet et al. [Acta Crystallogr. Sect. A 71, 20 (2015)], which has been adapted to differentiate between spatially adjacent phases and simultaneously track the evolution of those phases in response to electric fields. As a result, we have identified three environment specific GPEs. The first of these is a GPE which is an order of magnitude greater than previously reported for a given change in field. This is observed during a tetragonal-monoclinic transition in a multiphasic environment. A secondary, large GPE is observed in the neighboring, nontransitioning, monoclinic phase due to stress biasing, and a more typical GPE is observed when the system becomes monophasic. Our results demonstrate the simultaneous and complex interplay of intrinsic and extrinsic factors contributing to the GPE which is likely to have implications for device manufacture and miniaturization

Purification and characterization of 3,4-dihydroxyphenylalanine decarboxyase from pig kidney

A procedure for 3,4-dihydroxyphenylalanine decarboxylase from pig kkdney purification is described in detail. The preparation has no detectable impurity on electrophoresis and on ultracentrifugation and authors. However two significant differences are observed: a different stimulation of activity by added pyridoxal 5'-phosphate and a nearly complete decarboxylation of L-3,4-dihydroxyphenylalanine in absence of added coenzyme. Absorption, fluorescence and circular dichroism properties of the coenzyme-apoenzyme interaction are also described. The results are consistent with the existence of at least four coenzyme-apoenzyme complexes, three of them active