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Irrigation plays a fundamental role in advancing agricultural frontiers and increasing crop productivity, especially in semi-arid environments, because they exhibit high spatiotemporal rainfall variation. This practice is suggested even for adapted crops, such as forage cactus (Opuntia sp.), sorghum (Sorghum bicolor), and single or intercropping systems. In this study, aimed to evaluate the profitability of using irrigation in a single and intercropping forage cactus-sorghum system in a semi-arid region. The experimental design was in randomized blocks in a 5 × 3 factorial arrangement: five drip irrigation depths (0, 25, 50, 75, and 100% of the reference evapotranspiration - ET0) and three cropping systems (single forage cactus, single sorghum, and intercropping forage cactus-sorghum), with four replicates. The 0% ET0 treatment corresponded to rainfed conditions at a depth of 355 mm. A cycle of forage cactus and two sorghum cultivars (plant and regrowth) was conducted between November 2014 and November 2015. It was verified that the highest costs for implantation of the crop systems in irrigated conditions are due to the acquisition of irrigation and input systems, representing 85.3% of the effective operational cost. The single sorghum and forage cactus-sorghum systems provided the highest fresh matter productivity (62,013.05 and 60,075.36 kg ha-1, respectively). Based on economic indicators, the adoption of irrigation depths (25, 50, 75, and 100% ET0) promoted profits for the systems (single and intercropping) from the second year of implementation. RESUMO O uso da irrigação desempenha papel fundamental no avanço das fronteiras agrícolas e no aumento da produtividade nas áreas de cultivo, principalmente em ambientes semiáridos que apresentam alta variação espaço-temporal de chuvas. Essa prática é sugerida até mesmo para cultivos adaptados como palma forrageira (Opuntia sp.) e sorgo (Sorghum bicolor). Assim, objetivou-se avaliar a rentabilidade do uso da irrigação no sistema solteiro e sistema consorciado palma-sorgo no semiárido. O delineamento experimental foi em blocos casualizados em esquema fatorial 5 × 3: cinco lâminas de irrigação por gotejamento (0, 25, 50, 75 e 100% da evapotranspiração de referência - ET0) e três sistemas de cultivo (palma forrageira solteira, sorgo solteiro e consórcio palma-sorgo), com quatro repetições. O tratamento 0% ET0 correspondeu à condição de sequeiro com uma lâmina de 355 mm. Foi conduzido um ciclo de palma e dois de sorgo (planta e rebrota) compreendidos de novembro 2014 a novembro de 2015. Verificou-se que os maiores custos para implantação dos sistemas de cultivo em condições irrigadas se devem à aquisição do sistema de irrigação e insumos, representando 85,3% do custo operacional efetivo. O sistema sorgo solteiro e o sistema palma forrageira-sorgo proporcionaram as maiores produtividades de matéria fresca (62.013,05 e 60.075,36 kg ha-1), respectivamente. Com base em indicadores econômicos, a adoção de lâminas de irrigação (25, 50, 75 e 100% ET0) promoveu lucros para os sistemas (solteiro e consorciado) a partir do segundo ano de implantação.

Samples of superconducting Bi1.65Pb0.35Sr2Ca2 Cu3O10+δ (Bi-2223) with nanoparticle-sized grains were produced with the help of high-energy ball milling, followed by pelletizing, and flash sintering. X-ray powder diffraction patterns suggest that the grain size was not altered by flash sintering. The temperature dependence of the magnetic susceptibility χ ( T ) , electrical resistivity ρ ( T ) , and thermoelectric potential S ( T ) , all revealed features consistent with superconductivity below T c ≈ 108 K, though these features were progressively suppressed with the milling time. These data indicate that milling generates nanoparticle-sized grains with the Bi-2223 phase at the core, surrounded by a severely damaged and disordered outer shell. The thickness of this outer layer increases with milling time. The extent of the damage surrounding the grain cores has severe implications on the properties of the pellets. While the onset of superconductivity is clearly marked by the diamagnetic response in χ ( T ) , and a drop in S ( T ) , the signature in ρ ( T ) is more subtle and difficult to resolve, as it is superimposed on a semiconducting-like resistivity background. Measurements of the real ( e ′ ) and imaginary ( e ″ ) components of the dielectric permittivity in the low frequency limit reveal two distinct interfaces of charge accumulation, one at the margins between the crystalline grain cores and the damaged outer layers, and the second between the grain boundaries. The behaviors of ρ ( T ) and e ″ near room temperature follow closely an Arrhenius dependence, yielding activation energies in the range between 50 and 200 meV. The transport properties can be explained by a hopping model.

In the present work we demonstrate that C-doped Zr$_{5}$Pt$_{3}$ is an electron-phonon superconductor (with critical temperature T$_\mathrm{C}$ = 3.7\,K) with a nonsymmorphic topological Dirac nodal-line semimetal state, which we report here for the first time. The superconducting properties of Zr$_{5}$Pt$_{3}$C$_{0.5}$ have been investigated by means of magnetization and muon spin rotation and relaxation ($\mu$SR) measurements. We find that at low temperatures the depolarization rate is almost constant and can be well described by a single-band $s-$wave model with a superconducting gap of $2\Delta(0)/k_\mathrm{B}T_\mathrm{C}$ = 3.84, close to the value of BCS theory. From transverse field $\mu$SR analysis we estimate the London penetration depth $\lambda_{L}$ = 469 nm, superconducting carrier density $n_{s}$ = 2$\times$10$^{26}$ $m^{-3}$, and effective mass m$^{*}$ = 1.584 $m_{e}$. Zero field $\mu$SR confirms the absence of any spontaneous magnetic moment in the superconducting ground state. To gain additional insights into the electronic ground state of C-doped Zr$_5$Pt$_3$, we have also performed first-principles calculations within the framework of density functional theory (DFT). The observed homogenous electronic character of the Fermi surface as well as the mutual decrease of $T_\mathrm{C}$ and density of states at the Fermi level are consistent with the experimental findings. However, the band structure reveals the presence of robust, gapless fourfold-degenarate nodal lines protected by $6_{3}$ screw rotations and glide mirror planes. Therefore, Zr$_5$Pt$_3$ represents a novel, unprecedented condensed matter system to investigate the intricate interplay between superconductivity and topology., Comment: 9 pages, 5 figures

A preliminary study of the magnetic relaxation in (Bi, Pb)-2223 superconducting ceramics doped with α -Al 2 O 3 nanoparticles is presented, taking as starting point the measurements of the M ( t ) dependence, both in samples in the form of powder as in pellet. The relaxation of the three types of vortices that can exist inside these materials is analyzed, emphasizing on the intragranular region where the planar defects exist and, consequently, Abrikosov-Josephson vortices emerge. Finally, interesting results of the comparison between the behavior of the samples in the form of powder and in the form of pellet are shown from the estimation of the pinning energy of the vortices.

By combining experimental results and a simple model, we offer here an explanation for the role played by the low-angle grain boundaries and the doping with α-Al2O3 nanoparticles in the trapping of the magnetic flux in Bi1.65Pb0.35Sr2Ca2Cu3O10+δ (Bi-2223) ceramic samples. Our model correlates the size of the nanoparticles, properties of the superconducting matrix, and the magnetic flux trapped at the intragranular planar defects, the so-called Abrikosov-Josephson vortices. The results indicate that the role played by the doping with α-Al2O3 nanoparticles is to pin the AJ vortices at the grain boundaries with misorientation angles $\theta \sim 10^{\circ }$. We also argue that a similar procedure for identifying conditions for the trapping of the magnetic flux may be applied to other superconducting materials doped with non-magnetic nanoparticles.

Materiais do tipo \'La IND. 0.7-X\' \'Y IND.X\' \'Ca IND. 0.3\' MnO IND.0.99\' \'ANTPOT.57 \'Fe IND. 0.01\' \'O IND.3\' ; \'X = 0 e 0.10 ; foram produzidos através do método de precursores sol-gel. Resultados das análises dos diagramas de difração de raios-X indicaram que os materiais são de fase única e que houve uma substituição efetiva do Fe no sítio do Mn, sem provocar distorções significativas na cela unitária da estrutura cristalina do \'La IND. 0.60\' Y IND. 0.10\' \'Ca IND. 0.30\' \'MnO IND.3\' . Resultados das análises de \'ro\'(T) e M(T) revelaram que a pequena substituição de Fe altera a temperatura de Curie \'T IND.C\' assim como a temperatura de transição metal-isolante \'T IND.MI\' do sistema. A análise dos resultados de espectroscopia Mössbauer revela a coexistência e competição de duas fases magneticamente ordenadas e uma paramagnética em uma ampla região de temperatura compreendida entre 20 e 80 K. Resultados de resistividade elétrica a presença de campo magnético externo revelaram que ambas as amostras apresentam um efeito de magnetorresistência colossal MRC. Este efeito de MRC foi observado ocorrer em uma faixa de temperatura similar à faixa de temperatura onde a variação da fração volumétrica das fases ordenadas é máxima. Amostras de \'La IND. 0.60\' \'Y IND.0.10\' \'Ca IND. 0.3\' \'MnO IND.3\' foram produzidas com diferentes interfaces e/ou porosidades mas mantendo o mesmo tamanho de grão. Isto foi feito através da compactação e sinterização do pó de óxido de manganês e terra-rara misturado com diferentes proporções volumétricas P = 0, 10, 20 e 30% de um polímero. O resultado da análise termogravimétrica indicou uma oxidação total do polímero e a ausência de resíduos em temperaturas acima de 500 \'GRAUS\'C. Medidas de difração de raios-X mostraram que os materiais produzidos são monofásicos e que não ocorreu reação química entre o poliméro e o pó de \'La IND. 0.60\' \'Y IND. 0.10\' \'Ca IND. 0.3\' MnO IND.3\'. As medidas de ) porosimetria ao mercúrio PHg e as observaçãoes no microscópio eletrônico e varredura MEV indicaram que os materias possuem diferentes densidades de poros, tamanho de grão essencialmente constante e da ordem de 0.5 \'mu\'m. Medidas de magnetização M(T), resistividade elétrica \'ro\'(T) e principalmente resistividade elétrica com campo magnético aplicado \'ro\'(T, H), foram comparados entre as amostras com diferentes interfaces. Os resultados das medidas de resistência elétrica na presença de H indicaram que o comportamento de \'ro\'(H)\' \'ro\'(H=0) é essencialmente o mesmo entre as amostras com P=0 e 30% de poros. Este resultado sugere que o efeito de MRC é fracamente dependente da densidade de poros. Analisando-se os resultados de espectroscopia de impedância X(T, \'omega\'), nas amostras com P=0 e 30% de poros, foi possível observar duas contribuições para R(T) com tempos de relaxação diferentes. Entretanto, não foi possível atribuí-los aos grãos e contornos, mas a outros processos com diferentes dinâmicas do tipo spin-rede no material. Isso sugere que esses diferentes processos de relaxação ocorrem em regiões micrométricas, distintas e localizadas dentro do grão. O efeito de magnetorresistência intergranular MRI foi associado ao processo de tunelamento de spins, polarizados entre estas regiões diminutas dentro do grão, e não necessariamente entre os grãos físicos destes materiais. Microstructural control and intergranular magnetoresistance in manganites \'La IND. 0.7-X\' \'Y IND.X\' \'Ca IND. 0.3\' \'MnO IND.3\' ;X=0.0 and 0.1

In the present work, we demonstrate that C-doped Zr

The effects of Fe3O4 nanoparticles (NPs) and Rhizobium inoculation on nodulation, nitrogen fixation and plant growth of common bean (cv. Red Guama, Phaseolus vulgaris) plants were investigated in growth chambers. Plants were exposed to: Fe3O4 NPs (2000 mg/L) (T1), Rhizobium inoculation (T2) and Fe3O4 NPs + Rhizobium inoculation (T3); non-treated plants were considered as controls. Harvested 35-day-old treated plants showed improved symbiotic performance including increased nitrogenase activity (51.2–90.7%), nodule leghaemoglobin (44.8–80.9%) and iron content (83.4–84.2%), number of active nodules per plant (58.7–122%) and nodule dry weight (40.2–70.6%). This resulted in enhanced symbiotic nitrogen fixation,and increased shoot (26.5–50.2%) and root (24.1–48.2%) total nitrogen content in treated plants in comparison with the controls. The best result was obtained using treatment T3. Furthermore, Fe3O4 NPs were taken up by bean plants in treatments T1 and T3, and these accumulated in their organs, including in nodules. All treatments led to an increase in root (51.9–79.8%) and shoot (27.5–52.7%) lengths, in leaf area (10.9–16.8%) and in root (10.1–17.8%), stem (9.8–12.7%) and leaf dry weight (8–17.3%) compared to control plants. Thus applied treatments have the potential to improve common bean plant growth through enhancement of nodulation and nitrogen fixation during vegetative growth.This study also provides strong evidence that the presence Fe3O4 NPs in nodules improves the symbiotic performance between Rhizobium (leguminosarum CF1 strain) and the common bean plant, due to enhanced nodulation and nitrogen fixation.

We have performed valence-band resonant photoemission spectroscopy across the transition-metal (TM) ${L}_{3}$ edge of ${\mathrm{Rh}}_{2}{\mathrm{O}}_{3}, {\mathrm{RuO}}_{2}$, and ${\mathrm{MoO}}_{2}$. This technique allows us to access important information on the partial contribution of each respective TM. We show that an extended cluster model, coupled with transitions between discrete and continua states, describes well the overall resonance behavior as well as the experimental constant initial-state (CIS) spectra. Moreover, we analyze the resonant enhancement of the main lines and satellite structures to discuss the influence of the different charge regimes, the TM--O $2p$ hybridization, and additional charge screenings to the CIS signal. Finally, we argue that this approach can be extended to the study of other transition-metal oxides.

We have studied the effect of the pelletization pressure on microstructural and electrical transport properties of superconducting ceramics with starting composition given by the formula $$\text {Bi}_{1.65}\text {Pb}_{0.35}\text {Sr}_2\text {Ca}_{2.5}\text {Cu}_{3.5}\text {O}_{10+\delta }$$ . The experimental data of electrical measurements was processed in order to obtain the weak-link resistivity, the orientation probability of the grains’ a-axes along a certain preferential direction, the slope of the linear part in the temperature dependence of the ab-planes resistivity, and the intrinsic effective anisotropy of the grains, of each sample. In contrast with the behaviour of $$\text {Bi}_{1.65}\text {Pb}_{0.35}\text {Sr}_2\text {Ca}_{2}\text {Cu}_{3}\text {O}_{10+\delta }$$ ceramics, the Ca, Cu enriched samples exhibit a reduction of their effective anisotropy at sample level and weak links resistivity with increasing compacting pressures. In addition, a compacting pressure of around 488 MPa may affect considerably the electrical and structural parameters of the material. The results suggest that a combined effect of the pelletization pressure and the doping with Ca and Cu can be used to improve the electrical transport properties of these materials for technological applications.

We have observed a change in the behaviour of voltage-relaxation curves with remnant magnetic flux, when the maximum magnetic field applied before starting the relaxation process, $$H_{am}$$, reaches 80 Oe in two samples of $$\hbox {Bi}_{1.65}\hbox {Pb}_{0.35}\hbox {Sr}_{2}\hbox {Ca}_{2}\hbox {Cu}_{3}\hbox {O}_{10+\delta }$$ (Bi-2223) doped with $$\alpha $$-$$\hbox {Al}_{2}\hbox {O}_{3}$$ nanoparticles. This modification consists in the emergence of a maximum in the temporal dependence of the voltage, V(t), which appears in the vicinity of the first 5 s after applying to the sample an excitation current lightly higher than the superconducting critical current of the material. In addition to that, the voltage drop rate increases appreciably with increasing applied magnetic fields. As complementary studies, X-ray diffraction patterns, scanning electron microscopy, measurements of magnetization as a function of applied magnetic field and critical current density are also included. The experimental results corroborate the occurrence of intragranular Abrikosov–Josephson vortices in Bi-2223 ceramic superconductors. Furthermore, the analysis provides a new procedure for detecting penetration of the magnetic flux into intragranular planar defects and clean regions of the grains (crystallites), with increasing applied maximum magnetic field, $$H_{am}$$.

We study the electronic structure of GdCrTiO 5 polycrystals by means of magnetic susceptibility and heat capacity measurements, as well as x-ray absorption spectroscopies on the Cr 2 p , Ti 2 p and O 1 s levels. The experimental results were interpreted with Charge Transfer Multiplet and Density Functional Theory calculations. Magnetic susceptibility and specific heat measurements indicate a long-range antiferromagnetic ordering at 0.9 K probably related to the Gd sublattice. The results indicate that spin-orbit interaction, rather than hybridization, may be crucial for the stabilization of magnetic ordering in the RCrTiO 5 (R = rare earth) family.

Magnetic separation can be considered a green technology because it is fast, efficient, consumes low energy, and minimizes the use of solvents and the generation of waste. It has been successfully used in laboratory scale to facilitate supported catalysts’ handling, separation, recovery, and recycling. Only few materials are intrisically magnetic, hence the application of magnetic materials as catalyst supports has broaden the use of magnetic separation. Iron oxides, silica-coated iron oxides, and carbon-coated-cobalt are among the most studied catalyst supports; however, other metal oxide coatings, such as ceria and titania, are also very interesting for application in catalysis. Here we report the preparation of magnetically recoverable magnetic supports containing silica, ceria, and titania. We found that the silica shell protects the iron oxide core and allows the crystalization of ceria and titania at high temperature without compromising the magnetic properties of the catalyst supports.

The Abrikosov–Josephson (AJ) vortices that emerge at intragranular defects of Bi-2223 bulk superconductors are detected. The study is based on the combination of magnetic and transport characterizations with a brief theoretical formulation that allow estimating the minimum angle of the intragranular planar defects where the AJ vortices emerges for a given applied magnetic field. Measurements of magnetization versus applied magnetic field, $$M(H_{a})$$ , in powder samples reveal that the intrinsic anisotropy effects of the grains in these materials suffer almost a complete attenuation due to their high shape anisotropy. In fact, powder samples behave as composed of isotropic grains with lower critical field ~80 Oe. However, a more detailed analysis of the quasi-linear part of these curves show that the penetration of the magnetic flux into intragranular defects occurs at similar values of applied magnetic fields than those reported in whiskers or well textured ceramics for their two main perpendicular directions which are lower values than ~80 Oe. Finally, taking into account a brief theoretical formulation, we have found that in the case of defects where the magnetic flux penetrates perpendicular to the c-axis of the crystallites (~30 Oe) approximately the stacking faults and defects with misorientation angles higher than ~14 $$^{\circ }$$ can be the main causes of flux-trapping, but the mechanism may change to low misorientation angles defects, less than ~6 $$^{\circ }$$ , when the intergranular magnetic field is approximately parallel to the c-axis (~60 Oe).

In this paper we present a new method to determine separately inter and intragranular magnitudes of polycrystalline superconducting materials, such as: intrinsic effective anisotropy, $$t=\rho _c/\rho _{ab}$$ , the slope of the linear part in the temperature dependence of the ab-planes resistivity, $$A_{ab}=\Delta \rho _{ab}/\Delta T$$ , the weak links resistivity, $$\rho _{wl}$$ , and the orientation probability of the grains’ a-axes along a certain preferential direction, $$\gamma _{xa}$$ . Here, $$\rho _{ab}$$ , $$\rho _{c}$$ and T are the main values of the resistivitity tensor and the measurement temperature, respectively. The application of the method, illustrated by two (Bi,Pb)2223 polycrystalline samples, allows comparing the parameters obtained for the grains with those reported in single crystals. Moreover, we have demonstrated that different compacting pressures in the fabrication of the pellets change not only the inter, but also the intragranular properties of the ceramics. The method could be used to follow the different steps during the synthesis of polycrystalline high $$T_{c}$$ superconductors in order to optimise the process.

The influence of different plungers/die materials for the synthesis of (Bi, Pb) 2 Sr 2 Ca 2 Cu 3 O 10+ δ (Bi-2223) superconductors via the spark plasma sintering SPS method and by using two different setups made of all-graphite and all-steel were investigated. AISI H13 die steel, which is widely used as a hot forging die, was chosen to verify the methodology. In the all-steel setup, samples were consolidated at 700 and 750 °C, for 5 min, and subjected to two different heating rates of 135 and 50 °C/min. Moreover, by using the all-graphite setup, a sample was consolidated at 750 °C, for 5 min by using a heating rate of 145 °C/min. Irrespective of the type of plungers/die materials used, the X-ray diffraction analysis indicate the occurrence of an extra phase Bi 2 Sr 2 CaCu 2 O 8+ δ (Bi-2212) in all samples and its volume fraction was estimated to be comprehended between ∼3% and 60%. In samples consolidated with the all-steel setup at 750 °C, for 5 min, and a heating rate of 50 °C/min, the volume fraction of the Bi-2212 phase was found to be as high as 60%. Computational simulations, by using the Finite Element Method (FEM) with an integrated PID control, were performed to evaluate the temperature profile within samples during the SPS consolidation. The model was then validated by comparing its predictions with experimental results, showing good agreement. From the temperature dependence of magnetization M ( T ) , performed in powder and pellet samples, we have inferred that superconductivity arises from grains with core-shell morphology, where the shell is oxygen deficient. The influence of carbon contamination as the mechanism responsible for the oxygen deficiency in SPS samples has been considered and refuted by the current data. No evidence of the role played by the carbon contamination or reduction in promoting the formation of grains with core-shell morphology has been found. We also argue that the consolidation process, conducted under vacuum, is responsible for the origin of an oxygen deficiency shell near grain boundaries in Bi-2223 samples.

The impact of the grain boundary misorientation distribution (GBMD) on the intergranular voltage relaxation (V − t) curves at zero applied magnetic field in Bi1.65Pb0.35Sr2Ca2Cu3 O 10+δ (Bi-2223) ceramic samples has been investigated. Changes in the GMBD were realized by subjecting powders of Bi-2223 to two different uniaxial compacting pressures (UCP) before the last heat treatment of the samples. The GBMD was then determined from X-ray rocking curves and revealed significant differences between intergranular media of the specimens. It was found that the UCP results in a two-time reduction in the population of high-angle grain boundaries (𝜃 > 12∘) while the orientation homogeneity of the grain boundaries rises ∼ 30 %, indicating an improvement of the degree of texture of the materials. Such changes are mirrored in the behavior of the V − t curves which are explained by invoking differences in the rearrangement of the transport current driven by the angular dependence of the critical current density along grain boundaries. Numerical simulations of the V − t curves support the experimental V − t results and further suggest the occurrence of current localization in conductive paths within the materials.

We have compared the dependence of the critical current density on maximum applied magnetic field, Jc(0, Ham), performed in pellets with the derivative of magnetization versus applied magnetic field, dM(Ha)/dHa, of the corresponding powder samples of Bi 1.65 Pb 0.35 Sr 2 Ca 2 + x Cu 3 + x O y samples; x = 0.2 and 0.5. In both cases the measurements were performed at 77 K. We have focused in the applied magnetic field range in which the magnetization as a function of applied magnetic field, M(Ha), is quasi-linear. The comparison reveals that the penetration of the magnetic flux within powder particles is closely related to the trapped flux observed by means of the Jc(0, Ham) dependence in pellet samples. The combined results are well explained within the framework of the three-level superconducting model. The results also suggest that the magnetic flux, for applied magnetic fields Ha ranged from ∼30 to ∼80 Oe, first penetrates the intragranular planar defects, as stacking faults and/or colonies of low angle boundaries, while the magnetic flux penetration in regions free of defects is observed for higher values of Ha. As a correlative result, we have observed a decrease of the superconducting critical temperature of the crystallites TC with increasing x, which may be related with an increase of the number of stacking faults of the material.

We studied the partial contributions to the valence band spectra of MoO2, RuO2 and Rh2O3. The experimental technique of choice was the Cooper minimum method to X-ray photoemission spectroscopy. The spectra were interpreted with an extended cluster model and compared to usual band structure calculations. We conclude that, for the correct description of the valence band, one must include charge transfer, final-state and many-body effects in the description of the electronic structure of these compounds, which can also be extended to other systems.

Based on transport measurements performed on Bi-2223 polycrystalline superconductors, we have determined the in-plane resistivity, $$\rho _{ab}(T)$$ , the effective grain resistivity, $$\rho _g(T)$$ , and the effective intergranular resistivity, $$\rho _j(T)$$ , by applying a model recently reported by our group. The obtained dependencies allowed us to determine the critical temperatures of ab planes, grains as a whole, and intergranular junctions for four different polycrystalline samples. In addition, we were able to propose a very simple and general method to determine the first two critical temperatures previously mentioned by using measurements performed in polycrystalline superconducting samples comprised by highly anisotropic crystallites. Finally, our results may explain the two-step superconducting transition, observed in the samples set, as a feature of this compound linked to its high electrical anisotropy.

The effect of Fe3O4 nanoparticles (NPs) on chemical properties of the soil rhizosphere and on the accumulation of nutrients in common bean plants was studied for two different concentrations of Fe3O4 NPs. The root-to-leaves translocation index for micro- and macronutrients was calculated. The results showed that Fe3O4 NP treatments had a significant effect ( $$P < 0.05$$ ) on the chemical properties of soil rhizosphere in terms of an increase in the contents of total P, extractable P, total K, extractable K, Ca, total Mn, total Fe and cation exchange capacity and of a decrease in Cl content in soil. The treatments led to a marked increase in the accumulation of nutrients in plants by revealing a higher content of total P, K, Ca, Mn and Fe in roots, stems and leaves. In addition, the plants treated with Fe3O4 NPs showed lower translocation of total Mn and Fe to stems and leaves compared with the control plants. The results indicate that Fe3O4 NPs may contribute to the conversion of the insoluble forms of total P, extractable P, total K, extractable K, Ca, total Mn and total Fe in soil into soluble forms that can dissolve in the soil solution and be taken up by plants. A greater capability in the roots, stems and leaves of Fe3O4-NP-treated plants to take up the nutrients suggests a beneficial effect for plant development and health. Likewise, the roots of plants treated with Fe3O4 NPs absorbed and accumulated the greatest quantities of Mn and Fe compared with the control plants.

Magnetic properties of dilute single crystals of ${\mathrm{Gd}}_{1\ensuremath{-}x}{\mathrm{Y}}_{x}{\mathrm{B}}_{4}$ ($x=0$, 0.2, and 0.4) were systematically studied. These antiferromagnetic Shastry-Sutherland compounds display a remnant magnetization $M{}_{\mathrm{R}}$ when field cooled below the N\'eel temperature ${T}_{\mathrm{N}}$. The magnitude of $M{}_{\mathrm{R}}$ at low magnetic fields is magnetic field dependent, increasing with increasing magnetic fields, and it saturates for $H\ensuremath{\le}30$ Oe. The ${M}_{R}(T)$ data for both $x\phantom{\rule{0.16em}{0ex}}=\phantom{\rule{0.16em}{0ex}}0.2$ and 0.4 compositions overlap, and the remnant magnetization follows a universal behavior. We argue that these findings are explained by taking into account the formation of magnetic domains within the crystals, originating from the dilution of a magnetically frustrated, antiferromagnetic sublattice.

The nonmonotonic behavior of the magnetic field dependence H of the superparamagnetic blocking temperature TB(H) (or Tmax(H)) of an assembly of magnetic nanoparticles NPs was studied both experimentally and theoretically. We have combined the measurements of zero-field cooling ZFC magnetization curves under H performed on samples with increasing concentration of Ni nanoparticles and Monte Carlo simulations. As a result, we have found that increasing the strength of the dipolar interaction between granules and the occurrence of a very narrow width of a log-normal volume particle size distribution of the NPs suppress the nonmonotonic behavior of Tmax(H).

Powders of single-phase Bi1.65Pb0.35 Sr2Ca2Cu3O10+δ (Bi-2223) were consolidated by the spark plasma sintering (SPS) method at 750 ∘C. The SPS samples exhibited very high density, but are oxygen deficient, as inferred from magnetization, M(T), data. Therefore, the samples were then subjected to a post-annealing heat treatment in air, at 750 ∘C for 5 min. From the combined data of X-ray diffraction, microstructures observed by SEM, and Vickers microhardness measurements, we have found that SPS post-annealed samples showed the presence of an extra phase. According to the EDS analysis and X-ray diffraction results, the extra was identified as an infinite layer compound with general formula Ca1−x Sr x CuO2. Irrespective of the presence of this additional phase, the superconducting properties of post-annealed SPS samples are optimized when they are heat treated in air, at 750 ∘C for just 5 min. We have also observed a decrease in the Vickers as well as different indentation features in post-annelaed samples when compared with SPS ones. The occurrence of a decohesion of grains has been also observed, a feature similar to that found previously in the same material. On the other hand, a pile up formation occurred throughout the indentation in the sample, in which the annealing was carried out. 3-D profilometer characterizations confirmed these results, which are close related to the occurrence of the extra phase Ca1−x Sr x CuO2.

A systematic study of the superconducting properties in a series of arc-melted Nb-B samples close to the 1:1 composition was carried out. Powder X-ray diffraction (XRD) shows that all samples are both non-stoichiometric, and comprising of two crystal phases: a majority orthorhombic NbB-type phase, and traces of a minor body-centered cubic Nb-rich phase Nb$_{ss}$ with stoichiometry close to Nb$_{0.98}$B$_{0.02}$. The emergence of superconductivity near T$_c \sim$ 9.0 K was inferred from magnetization data in chunk and powder samples. However, the very small superconducting volume fractions are inconsistent with superconductivity arising from the major NbB phase. On the other hand, micrographs of selected samples clearly show that the minority Nb$_{ss}$ forms a three-dimensional network of filaments that meander around the grains of the majority phase, forming a percolation path. Here we report the superconductivity of the Nb$_{ss}$ phase, and argue that the low superconducting volume fraction of non-stoichiometric NbB and zero resistance are due to the filaments of the minority phase. The electronic contribution to the entropy of the superconducting state, yielded from an analysis using the alpha model for single-band systems, indicates that the Sommerfeld constant of the arc-melted samples is close to the values found in non-superconducting NbB. Micrograph, XRD, and bulk measurements of magnetization, electrical resistivity, and specific heat suggest that the superconducting state in the NbB samples bearing some Nb$_{ss}$ minority phase is due to the latter., 7 pages, 5 figures

The spin correlations and excitations of the Sr2YRuO6 double perovskite are investigated by means of Raman scattering, complemented by synchrotron X-ray diffraction measurements. Anomalous softening of a breathing mode of the oxygen octahedra is observed below ~200 K, much above the long-range antiferromagnetic ordering temperature, TN1 = 32 K, due to a spin-phonon coupling mechanism in the presence of magnetic correlations. A diffusive Raman signal is also observed, possibly associated with spin excitations within magnetically correlated regions. Our results point to a characteristic energy and temperature scale of ~25 meV/200 K below which unusual behavior associated with magnetic correlations is observed in this material. Copyright © 2013 John Wiley & Sons, Ltd.

We present structural, magnetic, electrical, thermal transport, Hall coefficient, and pressure-dependent resistivity measurements on $\mathrm{C}{\mathrm{u}}_{x}\mathrm{ZrT}{\mathrm{e}}_{2\ensuremath{-}y}$ compounds with $x=0.05$, 0.1, 0.15, 0.2, and 0.3, and $y$ varied between $0\ensuremath{\le}y\ensuremath{\le}0.8$. In order to calculate the ground state, ab initio calculations of the electronic structure of these materials were performed. Our results show that copper intercalation in $\mathrm{ZrT}{\mathrm{e}}_{2}$ induces superconductivity in the $\mathrm{ZrT}{\mathrm{e}}_{2}$ system. For the $\mathrm{C}{\mathrm{u}}_{0.3}\mathrm{ZrT}{\mathrm{e}}_{1.2}$ sample, Hall and Seebeck coefficient measurements show that the system is predominantly negatively charged with carrier density close to ${10}^{19}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}3}$. The temperature dependence of the Hall coefficient, the Seebeck coefficient, and the lower critical field indicates that this material presents multiband character. Pressure-dependent resistivity vs temperature measurements reveal that while the normal-state resistivity decreases with increasing applied pressure, the superconducting transition temperature is completely insensitive to the applied pressure (for pressure in the range 0--1.3 GPa). This suggests that the Fermi gas is intrinsically degenerate under very high pressure, and therefore does not change much with varying external pressure. Finally the band structure calculation shows a dispersion curve containing a bulk three-dimensional Dirac conelike feature at the L point in the Brillouin zone, which is gapless in the absence of spin-orbit coupling, but develops a gap when this coupling is considered. Altogether, the results indicate that the superconducting compound $\mathrm{C}{\mathrm{u}}_{x}\mathrm{ZrT}{\mathrm{e}}_{2\ensuremath{-}y}$ presents a signature of multiband behavior and may possibly be a new example of a topological superconductor.

We study the electronic structure of the ${\mathrm{Sr}}_{2}{\mathrm{YRuO}}_{6}$ and ${\mathrm{Sr}}_{2}{\mathrm{YRu}}_{0.75}{\mathrm{Ir}}_{0.25}{\mathrm{O}}_{6}$ compounds using x-ray (resonant) photoemission and absorption spectroscopies. The experimental results are interpreted with first-principles calculations, which give a good agreement with all the spectra. These results show that, although the spin-orbit coupling does not induce orbital anisotropies in these systems, it is responsible for the reduction of magnetic moments within the the ${\mathrm{Ir}}^{5+}{\text{O}}_{6}$ octahedra, weakening the magnetic ordering in the substituted system. Finally, our findings support the idea that the canting of ${\mathrm{Ru}}^{5+}$ magnetic moments actually plays an important role in the stabilization of the intriguing magnetic ordering in the ${\mathrm{Sr}}_{2}{\mathrm{YRuO}}_{6}$ compound.

The face-centered-cubic (fcc) lattice of ${\mathrm{Ru}}^{5+}$ spins in the double perovskite ${\mathrm{Sr}}_{2}{\mathrm{YRuO}}_{6}$ shows a delicate, three-dimensional antiferromagnetic (AFM) ground state composed of stacked square AFM layers. Inelastic neutron scattering data taken on this state reveal a gapped low-energy excitation band emerging from [001] with spin excitations extending to 8 meV. These magnetic excitations are modeled by a simple ${J}_{1}\text{\ensuremath{-}}{J}_{2}$ interaction scheme allowing quantitative comparisons with similar materials. At higher temperatures, the low-energy excitation spectrum is dominated by a quasielastic component associated with size fluctuations of two-dimensional AFM clusters that exhibit asymmetric correlations even at low temperatures. Thus, the fcc lattice in general and the double-perovskite structure in particular emerge as hosts of both two-dimensional and three-dimensional dynamics resulting from frustration.

We have conducted magnetoresistance measurements ρ(T,H) in applied magnetic fields up to 18 T in Bi1.65Pb0.35Sr2Ca2Cu3O10+δ ceramic samples which were subjected to different uniaxial compacting pressures. The anisotropic upper critical fields Hc2(T) were extracted from the ρ(T,H) data, yielding \(H^{ab}_{c2}(0) \sim 130~\mathrm{T}\) and the out-of-plane superconducting coherence length ξc(0)∼3 A. We have also estimated \(H^{c}_{c2}(0) \sim 4.4~\mathrm{T}\) and ξab(0) ∼90 A. In addition to this, a flux-line-lattice (FLL) melting temperature Tm has been identified as a second peak in the derivative of the magnetoresistance dρ/dT data close to the superconducting transition temperature. An Hm vs. T phase diagram was constructed and the FLL boundary lines were found to obey a temperature dependence Hm∝(Tc/T−1)α, where α∼2 for the sample subjected to the higher compacting pressure. A reasonable value of the Lindemann parameter cL∼0.29 has been found for all samples studied.

We report on experimental studies of the Kondo physics and the development of non-Fermi-liquid scaling in UCu4+xAl8−x family. We studied 7 different compounds with compositions between x=0 and 2. We measured electrical transport (down to 65 mK) and thermoelectric power (down to 1.8 K) as a function of temperature, hydrostatic pressure, and/or magnetic field. Compounds with Cu content below x=1.25 exhibit long-range antiferromagnetic order at low temperatures. Magnetic order is suppressed with increasing Cu content and our data indicate a possible quantum critical point at xcr≈1.15. For compounds with higher Cu content, non-Fermi-liquid behavior is observed. Non-Fermi-liquid scaling is inferred from electrical resistivity results for the x=1.25 and 1.5 compounds. For compounds with even higher Cu content, a sharp kink occurs in the resistivity data at low temperatures, and this may be indicative of another quantum critical point that occurs at higher Cu compositions. For the magnetically ordered compounds, hydrostatic pressure is found to increase the Neel temperature, which can be understood in terms of the Kondo physics. For the non-magnetic compounds, application of a magnetic field promotes a tendency toward Fermi-liquid behavior. Thermoelectric power was analyzed using a two-band Lorentzian model, and the results indicate one fairly narrow band (10 meV and below) and a second broad band (around hundred meV). The results imply that there are two relevant energy scales that need to be considered for the physics in this family of compounds.

Measurements of X-ray diffraction, electrical resistivity, and magnetization are reported across the Jahn–Teller phase transition in LaMnO3. Using a thermodynamic equation, we obtained the pressure derivative of the critical temperature (T JT ), dT JT /dP = −28.3 K GPa−1. This approach also reveals that 5.7(3)J (mol K)−1 comes from the volume change and 0.8(2) J (mol K)−1 from the magnetic exchange interaction change across the phase transition. Around T JT , a robust increase in the electrical conductivity takes place and the electronic entropy change, which is assumed to be negligible for the majority of electronic systems, was found to be 1.8(3) J (mol K)−1.

In this work, we report on the magnetic properties of nickel nanoparticles (NP) in a SiO2–C thin film matrix, prepared by a polymeric precursor method, with Ni content x in the 0–10 wt% range. Microstructural analyses of the films showed that the Ni NP are homogenously distributed in the SiO2–C matrix and have spherical shape with average diameter of ~10 nm. The magnetic properties reveal features of superparamagnetism with blocking temperatures T B ~ 10 K. The average diameter of the Ni NP, estimated from magnetization measurements, was found to be ~4 nm for the x = 3 wt% Ni sample, in excellent agreement with X-ray diffraction data. M versus H hysteresis loops indicated that the Ni NP are free from a surrounding oxide layer. We have also observed that coercivity (H C) develops appreciably below T B, and follows the H C ∝ [1 – (T/T B)0.5] relationship, a feature expected for randomly oriented and non-interacting nanoparticles. The extrapolation of H C to 0 K indicates that coercivity decreases with increasing x, suggesting that dipolar interactions may be relevant in films with x > 3 wt% Ni.

We report on the detection of the transport Barkhausen-like noise (TBN) in polycrystalline samples of Bi 1.65 Pb 0.35 Sr 2 Ca 2 Cu 3 O 10+ δ (Bi-2223) which were subjected to different uniaxial compacting pressures. The transport Barkhausen-like noise was measured when the sample was subjected to an ac triangular-shape magnetic field ( f ∼ 1 Hz) with maximum amplitude B max ≈ 5.5 mT, in order to avoid the flux penetration within the superconducting grains. Analysis of the TBN signal, measured for several values of excitation current density, indicated that the applied magnetic field in which the noise signal first appears, B a ( t i ), is closely related to the magnetic-flux pinning capability of the material. The combined results are consistent with the existence of three different superconducting levels within the samples: (i) the superconducting grains; (ii) the superconducting clusters; and (iii) the weak-links. We finally argue that TBN measurements constitute a powerful tool for probing features of the intergranular transport properties in polycrystalline samples of high- T c superconductors.

We have studied the normal and superconducting transport properties of Bi1.65Pb0.35Sr2Ca2Cu3O10+δ (Bi-2223) ceramic samples. Four samples, from the same batch, were prepared by the solid-state reaction method and pressed uniaxially at different compacting pressures, ranging from 90 to 250 MPa before the last heat treatment. From the temperature dependence of the electrical resistivity, combined with current conduction models for cuprates, we were able to separate contributions arising from both the grain misalignment and microstructural defects. The behavior of the critical current density as a function of temperature at zero applied magnetic field, Jc(T), was fitted to the relationship Jc(T)∝(1−T/Tc)n, with n≈ 2 in all samples. We have also investigated the behavior of the product Jcρsr, where ρsr is the specific resistance of the grain-boundary. The results were interpreted by considering the relation between these parameters and the grain-boundary angle, θ, with increasing the uniaxial compacting pressure. We have found that the above type of mechanical deformation improves the alignment of the grains. Consequently the samples exhibit an enhance in the intergranular properties, resulting in a decrease of the specific resistance of the grain-boundary and an increase in the critical current density.

Experimental and theoretical studies on the magnetic field dependence of the electrical resistance R ( B a ) and the transport noise (TN) in polycrystalline high- T c superconductors subjected to different uniaxial compacting pressures were conducted. X-ray diffraction rocking curves were performed in different surfaces of the samples in order to investigated the degree of texture. The results indicated an improvement of the degree of texture with increasing the uniaxial compacting pressure. In theoretical simulations of the data, the polycrystalline superconductors were described as a series-parallel array of Josephson devices. The intergranular magnetic field is described within the framework of the intragranular flux-trapping model and the distribution of the grain-boundary angles is assumed to follow the Rayleigh statistical function. The proposed model describes well the experimental magnetoresistance R ( B a ) data. We have found that the behavior of the R ( B a ) curves changes appreciably when different uniaxially compacting pressures are applied to the sample and such a changes are reproduced by the model when different grain-boundary angles distributions are used. In addition, changes in the R ( B a ) dependence have their counterparts in the experimental transport noise signals.

We here report the synthesis, characterization and catalytic performance of new supported Ru(III) and Ru(0) catalysts. In contrast to most supported catalysts, these new developed catalysts for oxidation and hydrogenation reactions were prepared using nearly the same synthetic strategy, and are easily recovered by magnetic separation from liquid phase reactions. The catalysts were found to be active in both forms, Ru(III) and Ru(0), for selective oxidation of alcohols and hydrogenation of olefins, respectively. The catalysts operate under mild conditions to activate molecular oxygen or molecular hydrogen to perform clean conversion of selected substrates. Aryl and alkyl alcohols were converted to aldehydes under mild conditions, with negligible metal leaching. If the metal is properly reduced, Ru(0) nanoparticles immobilized on the magnetic support surface are obtained, and the catalyst becomes active for hydrogenation reactions.

The disclosure of magnetic ionic liquids (MILs) as stable dispersions of surface modified γ-Fe2O3 or CoFe2O4 nanoparticles (NPs) in the 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIBF4) ionic liquid is reported. The magnetic NPs were characterized by X-ray powder diffraction, transmission electron microscopy, and Raman spectroscopy. The surface modified NPs have proved to form stable dispersions in BMIBF4 in the absence of water and behave like a magnetic ionic liquid. The MILs have been characterized by Raman spectroscopy, magnetic measurements, and DSC. The stability of the magnetic NPs in BMIBF4 is consistently explained by assuming the formation of a semiorganized protective layer composed of supramolecular aggregates in the form of [(BMI)2(BF4)3]−. A superparamagnetic behavior and saturation magnetization of ca. 18 emu/g for a sample containing 30% w/w maghemite NPs/BMIBF4 have been inferred from static and dynamic magnetic measurements. DSC results have shown that the MIL composed of 30% w/w ...

Nanoparticles of NiMn 2 O 4 were successfully obtained by mixing gelatin and inorganic salts NiCl 2 ·6H 2 O and MnCl 2 ·4H 2 O in aqueous solution. The mixture has been synthesized at different temperatures and resulted in NiMn 2 O 4 nanoparticles with crystallites size in the range of 14–44 nm, as inferred from X-ray powder diffraction (XRPD) data. We have also observed that both the average crystallite size and the unit cell parameters increase with increasing synthesis temperature. Magnetic measurements confirmed the presence of a magnetic transition near 110 K.

We here report the first magnetically recoverable Rh(0) nanoparticle-supported catalyst with extraordinary recovery and recycling properties. Magnetic separation has been suggested as a very promising technique to improve recovery of metal-based catalysts in liquid-phase batch reactions. The separation method is significantly simple, as it does not require filtration, decantation, centrifugation, or any other separation technique thereby, overcoming traditional time- and solvent-consuming procedures. Our new magnetically separable catalytic system, comprised of Rh nanoparticles immobilized on silica-coated magnetite nanoparticles, is highly active and could be reused for up to 20 times for hydrogenation of cyclohexene (180,000 mol/molRh) and benzene (11,550 mol/molRh) under mild conditions.

Common bean plants were grown in soil and irrigated with water solutions containing different concentrations of $$\hbox{Fe}_3\hbox{O}_4$$ nanoparticles (NPs) with a mean diameter close to 10 nm. No toxicity on plant growth has been detected as a consequence of Fe deficiency or excess in leaves. In order to track the $$\hbox{Fe}_3\hbox{O}_4$$ NPs, magnetization measurements were performed in soils and in three different dried organs of the plants: roots, stems, and leaves. Some magnetic features of both temperature and magnetic field dependence of magnetization M(T, H) arising from $$\hbox{Fe}_3\hbox{O}_4$$ NPs were identified in all the three organs of the plants. Based on the results of saturation magnetization $$M_\mathrm{s}$$ at 300 K, the estimated number of $$\hbox{Fe}_3\hbox{O}_4$$ NPs was found to increase from 2 to 3 times in leaves of common bean plants irrigated with solutions containing magnetic material. The combined results indicated that M(T, H) measurements, conducted in a wide range of temperature and applied magnetic fields up to 70 kOe, constitute a useful tool through which the uptake, translocation, and accumulation of magnetic nanoparticles by plant organs may be monitored and tracked.

We report on the application of the Resistively Shunted Junction (RSJ) model to granular high TC superconductors. Some derived predictions of the RSJ model are applied to a set of superconducting granular samples which can be considered as a network of Josephson junctions. The investigated samples belong to both holedoped Y1ixPrxBa2Cu3O7id (x = 0.0, 0.35, and 0.45) and the electron-doped Sm2ixCexCuO4id (x = 0:18) systems which display the so-called double resistive superconducting transition. We have performed several transport measurements in these compounds including temperature and magnetic field dependence of the electrical resistance, R(T; H), and I-V characteristics. Several aspects of the I-V characteristics were quantitatively well described by the RSJ model. The combined results strongly suggest that dissipation in granular superconducting samples is a natural consequence of the normal current flowing in parallel with the supercurrent current.

Measurements of the electrical resistivity as a function of temperature, ρ(T), for different values of applied magnetic field, Ba (0 ≤ Ba ≤ 50 mT), were performed in polycrystalline samples of Bi1.65Pb0.35Sr2Ca2 Cu3O10+δ subjected to different uniaxial compacting pressure (UCP). We have found appreciable differences in the grain orientation between samples by using X-ray diffractometry. From the X-ray diffraction patterns performed, in powder and pellet samples, we have estimated the Lotgering factor along the (00l) direction, F(00l). The results indicate that F(00l) increases ~23% with increasing UCP suggesting that grains of these samples are preferentially aligned along the c-axis, which is parallel to the compacting direction. The resistive transition of the samples have been interpreted in terms of the thermally activated flux-creep model. In addition, the effective intergranular pinning energy, U0, have been determined for different applied magnetic field. The magnetic field dependence of U0, for Ba > 8 mT, was found to follow a H- α dependence with α = 0.5 for all samples. The analysis of the experimental data strongly suggested that increasing UCP results in appreciable changes in both the grain alignment and the grain connectivity of the samples. We have successfully interpreted the data by considering the existence of three different superconducting levels within the samples: the superconducting grains, the weak-links, and the superconducting clusters.