Ruthenocuprates RuSr2(Eu,Ce)2Cu2O10: Intrinsic magnetic multilayers

We report ac susceptibility data on RuSr_2(Eu,Ce)_2Cu_2O_(10-y) (Ru-1222, Ce content x=0.5 and 1.0), RuSr_2GdCu_2O_8 (Ru-1212) and SrRuO_3. Both Ru-1222 (x=0.5, 1.0) sample types exhibit unexpected magnetic dynamics in low magnetic fields: logarithmic time relaxation, switching behavior, and `inverted' hysteresis loops. Neither Ru-1212 nor SrRuO_3 exhibit such magnetic dynamics. The results are interpreted as evidence of the complex magnetic order in Ru-1222. We propose a specific multilayer model to explain the data, and note that superconductivity in the ruthenocuprate is compatible with both the presence and absence of the magnetic dynamics.Comment: 9 pages, 11 figures, Revtex; submitted to Phys.Rev.

Interesting magnetic properties of Fe1−x_{1-x}Cox_xSi alloys

Solid solution between nonmagnetic narrow gap semiconductor FeSi and diamagnetic semi-metal CoSi gives rise to interesting metallic alloys with long-range helical magnetic ordering, for a wide range of intermediate concentration. We report various interesting magnetic properties of these alloys, including low temperature re-entrant spin-glass like behaviour and a novel inverted magnetic hysteresis loop. Role of Dzyaloshinski-Moriya interaction in the magnetic response of these non-centrosymmetric alloys is discussed.Comment: 11 pages and 3 figure

Strong dependence of the Fe thin-film magnetic anisotropy on the Si(111) substrate preparation

We report on the influence of the Si (111) surface preparation on both the structural and the magnetic properties of iron thin films grown onto them. Two different substrate preparation procedures were used, in one of which the substrate was purposely oxidized. The surface analysis was performed by using atomic force and scanning tunneling microscopies, and the magnetic behavior of the films was observed by magneto-optic Kerr effect polarimetry. A strong relationship between the substrate preparation procedure, morphology, and the magnetic response of the iron films was found. A phenomenological model was used to interpret the experimental magnetization data and to derive the anisotropy parameters for both types of Fe samples. It was found that the magnetic response of the film grown onto the oxidized substrate is dominated by the uniaxial anisotropy originated from the substrate topology (a terracelike structure); the behavior of the other film, grown onto the unoxidized substrate, is determined by both cubic and easy-plane anisotropies

Multiscale modelling approach for simulating low velocity impact tests of aramid-epoxy composite with nanofillers

The addition of nanofillers to composites has attracted great attention since it adds multifunctional potential. However, the presence of nanofillers inside a composite may cause a more complex response in many situations, e.g. damage accumulation processes, and this response poses extra challenges in the development of reliable numerical approaches. In this work, a three-step multiscale modelling strategy was used to investigate the mechanical properties and damage accumulation of plain-weave aramid-epoxy composites with hybrid nanofillers (carbon nanotubes and graphene nanoplatelets). First, the mean-field method was employed in a microscale model to provide the elastic modulus of the matrix with nanofillers inside. The mechanical properties of such a matrix were then used to predict the global mechanical properties of aramid-epoxy composite using mesoscale models. Finally, those predictions were added as input to a homogeneous material model used to replicate a more complex loading condition (low-velocity tests), for which the direct use of the mesoscale approach is not feasible. In the latter, the mechanical properties of aramid-epoxy composite with nanofillers have been modelled using MAT_162 in LS-DYNA. The agreement between the experiments and simulations with regards to the loading curves and damage phenomena can thus validate the presented approach. In addition, the effect of nanofillers on the mechanical properties and damage evolution of the woven composites in low-velocity impact has been discussed. Finally, the present work can be helpful to improve the awareness in the design of innovative materials by means of predictive modelling approaches

Magnetic-field-dependent morphology of self-organized Fe on stepped Si(111) surfaces

The present work reports on Fe thin films grown on vicinal Si(111) substrates via rf magnetron sputtering. The dependencies of the growth mode and magnetic properties of the obtained iron nanostructures on both crystallographic surface orientation and on the direction of the very weak stray magnetic field from the magnetron gun were studied. Scanning tunneling microscopy images showed strong dependence of the Fe grains’ orientation on the stray field direction in relation to the substrate’s steps demonstrating that, under appropriately directed magnetic field, Si surfaces can be used as templates for well-defined self-assembled iron nanostructures. Magneto-optical Kerr effect hysteresis loops showed an easy-axis coercivity almost one order of magnitude smaller for the film deposited with stray field applied along the steps, accompanied with a change in the magnetization reversal mode. Phenomenological models involving coherent rotation and/or domain-wall unpinning were used for the interpretation of these results

Radarsat-2 Backscattering for the Modeling of Biophysical Parameters of Regenerating Mangrove Forests

The aim of this study is to understand the relationship between radar backscattering (σ°, β° and γ) of a multi-polarized Radarsat-2 C-band image with the structural attributes of regenerating mangrove vegetation located at the mouth of the Amazon River. CBH (circumference at breast height), height and species data were collected to characterize vegetation structure and above-ground biomass (AGB) at 17 plots with a total of 3090 measured individuals. Significant relationships between the linear σ° in VH (vertical transmit, horizontal receive) cross-polarization produced r2 values of 0.63 for the average height, 0.53 for the DBH, 0.46 for the basal area (BA) and 0.52 for the AGB. Using co-polarized HH (horizontal transmit, horizontal receive) and VV (vertical transmit, vertical receive), r2 values increased to 0.81, 0.79, 0.67 and 0.79, respectively. Vegetation attribute maps of average canopy height, DBH and AGB were generated for the study area. We conclude that multi-polarized Radarsat-2 images were adequate for characterization of vegetation attributes in areas of mangrove regeneration