A systematic investigation on the structural, magnetic and magnetocaloric properties of Pr0.6Sr0.4–xAgxMnO3 (x=0.05 and 0.1) manganites was reported. Rietveld refinements of the X-ray diffraction patterns confirmed that all samples were single phase and crystallized in the orthorhombic structure with Pnma space group. Magnetic measurements in a magnetic applied field of 0.01 T revealed that the ferromagnetic-paramagnetic transition temperature TC decreased from about 293 to 290 K with increasing silver content from x=0.05 to 0.1. The reported magnetocaloric entropy change and relative cooling power for both samples were considerably remarkable with a ΔSmax value of 1.9 J/(kg·K) and maximum RCP values of 100 J/kg, under a magnetic field change (Δµ0H) equal to 1.8 T. The analysis of the universal curves gave an evidence of a second order magnetic transition for the studied samples. The magnetic field influence on both the magnetic entropy change and the relative cooling power was also studied and discussed.

The critical properties of monovalent doped manganite Pr0.55K0.05Sr0.4MnO3 around the paramagnetic to ferromagnetic phase transition were investigated through various methods: the modified Arrott plots (MAP), the Kouvel–Fisher method and the critical isotherm analysis. Data obtained near Tc were examined in the framework of the mean field theory, the 3D-Heisenberg model, the 3D-Ising model, and tricritical mean field. The deduced critical exponents values obtained using MAP method were found to be β=0.44(4) with TC≈303K and γ=1.04(1) with TC≈302K. Kouvel–Fisher method supplies the critical values to be β=0.41(2) with TC≈302K and γ=1.09(1) with TC≈302K. The obtained critical parameters show a tendency towards the mean-field behavior, suggesting the existence of long-range ferromagnetic order in the compound studied. The exponent δ deduced separately from isotherm analysis at T=303K was found to obey to the Widom scaling relation δ=1+γ/β. The reliability of obtained exponents was confirmed by using the universal scaling hypothesis. The itinerant character of ferromagnetism in the present system was also tested by using Rhodes–Wohlfarth's criterion.

Pr0.55K0.05Sr0.4MnO3 sample have been synthesized using the conventional solid state reaction. Rietveld refinements of the X-ray diffraction patterns at room temperature confirm that the sample is single phase and crystallizes in the orthorhombic structure with Pnma space group; the crystallite size is around 70 nm. The SEM images show that grain size spreads around 1000-1200 nm. DTA analysis does not reveal any clear transition in temperature range studied. The low-temperature DSC indicates that Curie temperature is around 297 K. Magnetization measurements in a magnetic applied field of 0.01 T exhibit a paramagnetic-ferromagnetic transition at the Curie temperature T-C = 303 K. A magnetic entropy change under an applied magnetic field of 2 T is found to be 2.26 J kg (1) K (1), resulting in a large relative cooling power around 70 J/kg. Electrical resistivity measurements reveal a transition from semiconductor to metallic phase. The thermal conductivity is found to be higher than that reported for undoped and Na doped manganites reported by Thaljaoui et al. (2013). (C) 2014 Elsevier B.V. All rights reserved.

Recently, we obtained a new Fe-Al-O fibrous material by applying the novel route of electrospinning. Here we report on the properties of the as prepared material established by PPMS magnetometry and X-ray diffraction. X-ray diffractograms revealed the coexistence of the orthorhombic multiferroic phase FeAlO3 along with traces of unreacted impurities. The structure of the FeAlO3 phase is described in the orthorhombic Pna2(1) space group and is of great current interest since the compound features piezoelectricity, ferrimagnetism and magnetoelectric effects at low temperatures. In contrast to known bulk material obtained by classical routes the new fibrous material shows a lower value of saturation magnetization and the magnetic transition occurs at a much lower temperature. In the discussion an attempt is made to disclose the reasons for the observed differences.

An orthorhombic DyMnO3 single crystal has been studied in magnetic fields up to 14T and between 3K and room temperature. The field dependent ordering temperature of Dy moments is deduced. The paramagnetic Curie Weiss behavior is related mainly to the Dy3+sublattice whereas the Mn sublattice contribution plays a secondary role. DC magnetization measurements show marked anisotropic features, related to the anisotropic structure of a cubic system stretched along a body diagonal, with a magnetic easy axis parallel to the crystallographic b axis. A temperature and field dependent spin flop transition is observed below 9K, when relatively weak magnetocrystalline anisotropy is overcome by magnetic fields up to 1.6T.

Basic principles of the electro-hydrodynamics are applied for synthesis of solid state Fe-Al-O multi-ferroic fibrous material. For that purpose stable blend spinning solutions comprised of a high molecular assisting organic polymer and salts of iron and aluminum are developed. These solutions are tested under electrospinning conditions and synthesis of homogeneous as spun non-woven mats characterized by fibre mean diameters in the micro-and nano-size range is successfully demonstrated. Multi-step thermal procedure is applied for the consecutive solvent evaporation, polymer pyrolisis and final fibre calcination. Electron-optical imaging technique and XRD are applied for revealing the sample morphology and the phase composition correspondingly. The results obtained outline the wide possibilities for fabrication of multi-ferroics fibrous nano-materials on the basis of Fe-Al-O.

Crystals of PrxLa1−xAlO3 solid solution have been grown by the Czochralski method for the first time, to the best of our knowledge. Crystals with high praseodymium concentration tend to grow spirally. The color of the crystals changes with chemical composition. X-ray diffraction shows an increase of the lattice constants with an increase in lanthanum ion concentration. The thermal conductivity has been investigated in the temperature range from 5 to 300 K. Completely different behavior of thermal conductivity is observed at low temperatures for the investigated crystals, whereas it remains roughly constant at high temperatures. The values of magnetic susceptibility lie within the expected range that could be expected for a paramagnetic material.

We report the high temperature thermoelectric properties of Ca1-xDyxMn1-yNbyO3-delta (x = 0, 0.02, 0.1 and y = 0, 0.02) synthesized by spray-drying method. A maximum power factor (PF) value of 2.65 mu WK-2 cm(-1) is obtained at 1100 K for CaMn0.98Nb0.02O3-delta. This represents an improvement of about 75% with respect to undoped CaMnO3-delta sample at the same temperature. We also provide a complete structural characterization of the samples. (C) 2011 Elsevier B.V. All rights reserved.

The magnetic anisotropy of rare-earth substituted 2212 materials (Bi2Sr2Ca0.8RE0.2Cu2Ox with RE = Gd, Dy, Ho, Er) is put into evidence. Superconducting powder dispersed in epoxy resin is oriented under an external magnetic field (4 T) in a direction that depends on the nature of the rare-earth used in the substitution. Both directions of observation (parallel or perpendicular to the field) were investigated. Splitting of (00l) peaks is neatly observed and discussed.

Synthesis of polycationic compounds by the spray-drying technique is an interesting alternative in the domain of aqueous precursor synthesis methods. Spray drying yields high quality samples with good reproducibility. The possibility of scaling up for production of large quantities with fast processing time is well established by the commercial availability of powders of various compositions. In this paper, we have discussed the advantages and limitations of this method and demonstrated its interest by synthesizing a few polycationic compounds selected for their attractive properties of thermoelectricity [Bi1.68Ca2Co1.69O8, La0.95A0.05CoO3 (A=Ca, Sr, Ba)] or magnetoresistance [La0.70A0.30MnO3 (A=Sr, Ba)]. We have confirmed the quality of these samples by reporting their structure, magnetic and transport properties.

We report the high temperature thermoelectric properties of Ca1-xDyxMn1-yNbyO3-δ (x = 0, 0.02, 0.1 and y = 0, 0.02 ) synthesized by spray-drying method. A maximum power factor (PF) value of 2.65 μW K -2 cm -1 is obtained at 1100 K for CaMn0.98Nb0.02O3-δ. This represents an improvement of about 75% with respect to undoped CaMnO3-δ sample at the same temperature. We also provide a complete structural characterization of the samples.

The trapped magnetic field is examined in bulk high-temperature superconductors that are artificially drilled along their c-axis. The influence of the hole pattern on the magnetization is studied and compared by means of numerical models and Hall probe mapping techniques. To this aim, we consider two bulk YBCO samples with a rectangular cross-section that are drilled each by six holes arranged either on a rectangular lattice (sample I) or on a centered rectangular lattice (sample II). For the numerical analysis, three different models are considered for calculating the trapped flux: (i), a two-dimensional (2D) Bean model neglecting demagnetizing effects and flux creep, (ii), a 2D finite-element model neglecting demagnetizing effects but incorporating magnetic relaxation in the form of an E-J power law, and, (iii), a 3D finite element analysis that takes into account both the finite height of the sample and flux creep effects. For the experimental analysis, the trapped magnetic flux density is measured above the sample surface by Hall probe mapping performed before and after the drilling process. The maximum trapped flux density in the drilled samples is found to be smaller than that in the plain samples. The smallest magnetization drop is found for sample II, with the centered rectangular lattice. This result is confirmed by the numerical models. In each sample, the relative drops that are calculated independently with the three different models are in good agreement. As observed experimentally, the magnetization drop calculated in the sample II is the smallest one and its relative value is comparable to the measured one. By contrast, the measured magnetization drop in sample (1) is much larger than that predicted by the simulations, most likely because of a change of the microstructure during the drilling process.

Structure, magnetic and magnetocaloric properties of poly- and nanocrystalline La0.5Ca0.5MnO3 manganites prepared by the citrate sol-gel method are studied in a broad temperature range. The Arrott plots show that the phase transition is of the second order. The cooling efficiency of 93-97J/kg is found for the poly- and nanocrystalline samples. The relatively weaker magnetocaloric effect in nanocrystalline La0.5Ca0.5MnO3 is spread over temperature range almost three times broader than for the polycrystalline one. Charge ordering effects decay in manganites with grain sizes below 150 nm. (C) 2010 Elsevier B.V. All rights reserved.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Physical properties of polycrystalline La0.5Ba0.5MnO3 are reported from low temperature (10 K) up to above room temperature. An aim has been to obtain microscopic parameters and to search for the characteristic lengths in terms of which one can discuss the interplay between magnetic, electric, and phonon excitations. The structural and magnetotransport measurements reveal a set of relatively high transition temperatures (near 300 K) between ferromagnetic/metallic and paramagnetic/semiconducting phases. It is found, in particular, that the so-called localization length increases from 0.085 to 0.24 nm when the magnetic field varies from 0 to 8 T. Moreover a “special field value” ∼0.03 T is observed in the description of the electrical resistance. It cannot be presently distinguished whether it is the signature of a spin reorientation transition in the canted phase or a mere saturation field for aligning magnetic domains. The relatively high magnetoresistance effect (≃55% at 8 T and 10 K) makes the La0.5Ba0.5MnO3 a very interesting material for among others sensor applications.

We report the temperature dependence of the thermal conductivity κ(T) of bulk polycrystalline composite samples containing a magnetoresistive manganite (La0.7Ca0.3MnO3) and an electrically insulating phase (Mn3O4). The sample porosity is shown to be a significant parameter affecting the experimental data: after porosity correction the curves display the characteristics of an ideal composite. A fit of the κ(T) curves at low temperature using the Debye model enables the mean free path of phonons scattered on “boundaries” to be determined. The values are on the order of the grain size but are influenced by the grain arrangement and the presence of twins.

We present a method for characterizing the propagation of the magnetic flux in an artificially drilled bulk high-temperature superconductor (HTS) during pulsed-field magnetization. As the magnetic pulse penetrates the cylindrical sample, the magnetic flux density is measured simultaneously in 16 holes by means of microcoils that are placed across the median plane, i.e. at an equal distance from the top and bottom surfaces, and close to the surface of the sample. We discuss the time evolution of the magnetic flux density in the holes during a pulse and measure the time taken by the external magnetic flux to reach each hole. Our data show that the flux front moves faster in the median plane than on the surface when penetrating the sample edge; it then proceeds faster along the surface than in the bulk as it penetrates the sample further. Once the pulse is over, the trapped flux density inside the central hole is found to be about twice as large in the median plane as on the surface. This ratio is confirmed by modelling.

The structural, magnetic and electrical transport properties of the Sn-doped TbMnO3 manganites are studied by X-ray diffraction, ac susceptibility, dc magnetization and electrical resistivity measurements. The Sn doping into the Tb and Mn sites of TbMnO3 compresses the unit cell and changes parameters of the antiferromagnetic phase whereas the magnetic moment of Mn are only weakly affected. The electrical resistivity of doped manganites is reduced and the activation energy EA is determined for the thermally activated conduction.