Magnetoresistance and collective Coulomb blockade in super-lattices of ferromagnetic CoFe nanoparticles

We report on transport properties of millimetric super-lattices of CoFe nanoparticles surrounded by organic ligands. R(T)s follow R(T) = R_0.exp(T/T_0)^0.5 with T_0 ranging from 13 to 256 K. At low temperature I(V)s follow I=K[(V-V_T)/V_T]^ksi with ksi ranging 3.5 to 5.2. I(V) superpose on a universal curve when shifted by a voltage proportional to the temperature. Between 1.8 and 10 K a high-field magnetoresistance with large amplitude and a strong voltage-dependence is observed. Its amplitude only depends on the magnetic field/temperature ratio. Its origin is attributed to the presence of paramagnetic states present at the surface or between the nanoparticles. Below 1.8 K, this high-field magnetoresistance abruptly disappears and inverse tunnelling magnetoresistance is observed, the amplitude of which does not exceed 1%. At this low temperature, some samples display in their I(V) characteristics abrupt and hysteretic transitions between the Coulomb blockade regime and the conductive regime. The increase of the current during these transitions can be as high as a factor 30. The electrical noise increases when the sample is near the transition. The application of a magnetic field decreases the voltage at which these transitions occur so magnetic-field induced transitions are also observed. Depending on the applied voltage, the temperature and the amplitude of the magnetic field, the magnetic-field induced transitions are either reversible or irreversible. These abrupt and hysteretic transitions are also observed in resistance-temperature measurements. They could be the soliton avalanches predicted by Sverdlov et al. [Phys. Rev. B 64, 041302 (R), 2001] or could also be interpreted as a true phase transition between a Coulomb glass phase to a liquid phase of electrons

Magnetic hyperthermia in single-domain monodisperse FeCo nanoparticles: Evidences for Stoner-Wohlfarth behaviour and large losses

We report on hyperthermia measurements on a colloidal solution of 15 nm monodisperse FeCo nanoparticles (NPs). Losses as a function of the magnetic field display a sharp increase followed by a plateau, which is what is expected for losses of ferromagnetic single-domain NPs. The frequency dependence of the coercive field is deduced from hyperthermia measurement and is in quantitative agreement with a simple model of non-interacting NPs. The measured losses (1.5 mJ/g) compare to the highest of the literature, though the saturation magnetization of the NPs is well below the bulk one.Comment: 14 pages, 3 figure

Feasibility of using rural waste products to increase the denitrification efficiency in a surface flow constructed wetland

A surface flow constructed wetland (CW) was set in the Lerma gully to decrease nitrate (NO3 -) pollution from agricultural runoff water. The water flow rate and NO3 - concentration were monitored at the inlet and the outlet, and sampling campaigns were performed which consisted of collecting six water samples along the CW flow line. After two years of operation, the NO3 - attenuation was limited at a flow rate of ~2.5 L/s and became negligible at ~5.5 L/s. The present work aimed to assess the feasibility of using rural waste products (wheat hay, corn stubble, and animal compost) to induce denitrification in the CW, to assess the effect of temperature on this process, and to trace the efficiency of the treatment by using isotopic tools. In the first stage, microcosm experiments were performed. Afterwards, the selected waste material was applied in the CW, and the treatment efficiency was evaluated by means of a chemical and isotopic characterization and using the isotopic fractionation (e) values calculated from laboratory experiments to avoid field-scale interference. The microcosms results showed that the stubble was the most appropriate material for application in the CW, but the denitrification rate was found to decrease with temperature. In the CW, biostimulation in autumn-winter promoted NO3 - attenuation between two weeks and one month (a reduction in NO3 - between 1.2 and 1.5 mM was achieved). After the biostimulation in spring-summer, the attenuation was maintained for approximately three months (NO3 - reduction between 0.1 and 1.5 mM). The e15NNO3/N2 and e18ONO3/N2 values obtained from the laboratory experiments allowed to estimate the induced denitrification percentage. At an approximate average flow rate of 16 L/s, at least 60% of NO3 - attenuation was achieved in the CW. The field samples exhibited a slope of 1.0 for d18O-NO3 - versus d15N-NO3 -, similar to those of the laboratory experiments (0.9–1.2). Plant uptake seemed to play a minor role in NO3 - attenuation in the CW. Hence, the application of stubble in the CW allowed the removal of large amounts of NO3 - from the Lerma gully, especially when applied during the warm months, but its efficacy was limited to a short time period (up to three months). © 2019 Elsevier B.V

Evaluating the potential use of a dairy industry residue to induce denitrification in polluted water bodies: a flow-through experiment

Improving the effectiveness and economics of strategies to remediate groundwater nitrate pollution is a matter of concern. In this context, the addition of whey into aquifers could provide a feasible solution to attenuate nitrate contamination by inducing heterotrophic denitrification, while recycling an industry residue. Before its application, the efficacy of the treatment must be studied at laboratory-scale to optimize the application strategy in order to avoid the generation of harmful intermediate compounds. To do this, a flow-through denitrification experiment using whey as organic C source was performed, and different C/N ratios and injection periodicities were tested. The collected samples were analyzed to determine the chemical and isotopic composition of N and C compounds. The results proved that whey could promote denitrification. Nitrate was completely removed when using either a 3.0 or 2.0 C/N ratio. However, daily injection with C/N ratios from 1.25 to 1.5 seemed advantageous, since this strategy decreased nitrate concentration to values below the threshold for water consumption while avoiding nitrite accumulation and whey release with the outflow. The isotopic results confirmed that nitrate attenuation was due to denitrification and that the production of DIC was related to bacterial whey oxidation. Furthermore, the isotopic data suggested that when denitrification was not complete, the outflow could present a mix of denitrified and nondenitrified water. The calculated isotopic fractionation values (ε15NNO3/N2 and ε18ONO3/N2) might be applied in the future to quantify the efficiency of the bioremediation treatments by whey application at field-scale

Numerical modeling of enhanced biodenitrification in a laboratory flow-through experiment

High concentration of nitrate (NO3) in water resources has become a widespread and important environmental contaminant, being anthropogenic nitrogen input the principal source of NO3− pollution (Arauzo, 2017). Underanaerobic conditions, microbial reduction of NO3 to N2(g) to oxidize dissolved organic carbon (DOC) is the principal NO3 attenuation process in groundwater aquifers (Matchett et al., 2019)

Nitrate and Nitrite Attenuation by Fe(II) Minerals: Biotic and Abiotic Reactions

Nitrate (NO3-) pollution of groundwaterhas become a relevant issue and anenvironmental priority as it is related toecological and human health problems(Rivett et al. 2008) and its concentration is still above the threshold limit of 50mg/L in many areas (Nitrate Directive, 91/676/EEC). Contamination sources of NO3 - are linked to extensive use of fertilizers, inappropriate placement of animal waste and spills from septic system effluents

Characterisation of the natural attenuation of chromium contamination in the presence of nitrate using isotopic methods. A case study from the Matanza-Riachuelo river basin, Argentina

The groundwater contamination by hexavalent chromium (Cr(VI)) in a site of the Matanza-Riachuelo River basin (MRB), Argentina, has been evaluated by determining the processes that control the natural mobility and attenuation of Cr(VI) in the presence of high nitrate (NO3−) contents. The groundwater Cr(VI) concentrations ranged between 1.9E-5 mM and 0.04 mM, while the NO3− concentrations ranged between 0.5 mM and 3.9 mM

Influence of structural and magnetic properties in the heating performance of multicore bioferrofluids

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY).Biomedical applications of superparamagnetic iron oxide particles have been of interest for quite a number of years. Recent developments show that multifunctionality can be efficiently achieved using polymers to coat the particles and to provide anchoring elements to their surface. This leads to the formation of nanobeads with a reduced number of particles trapped by the polymeric structure. While the magnetothermic behavior of isolated nanoparticles has been a subject of interest over the past several years, multicore magnetic nanobeads have thus far not received the same attention. The influence of structural and magnetic properties in the hyperthermia performance of a series of magnetic fluids designed for biomedical purposes is studied here. The fluids are made of maghemite multicore polymeric beads, with variable nanoparticle size and hydrodynamic size, dispersed in a buffer solution. The specific loss power (SLP) was measured from 5 to 100 kHz with a field intensity of 21.8 kA/m. SLP increases with increasing magnetic core size, reaching 32 W/g Fe 2O3 at 100 kHz for 16.2 nm. Within the framework of the linear response theory, a graphical construction is proposed to describe the interplay of both size distributions and magnetic properties in the heating performance of such fluids in a given frequency range. Furthermore, a numerical model is developed to calculate the spare contribution of Néel and Brown relaxation mechanisms to SLP, which gives a fair reproduction of the experimental data. © 2013 American Physical Society.R.B. would like to thank ICMA-CSIC for the JAE predoc grant. Financial support from Grant No. MAT2011-25991 is gratefully acknowledged. We acknowledge Fundaçâo para a Ciência e Tecnologia (FCT, Portugal), COMPETE, and FEDER programs (Pest-C/CTM/LA0011/2013). N.J.O.S. acknowledges FCT for the Ciência 2008 program.Peer Reviewe

The role of siderite on abiotic nitrite reduction by dissolved Fe(II)

Iron redox reactions affect the fate and transformation of groundwater NO3-. Fe(II) present in groundwater as dissolved Fe(II) or Fe(II) sorbed onto mineral surfaces is oxidised into Fe(III) (oxyhydr)oxides using NO3- as an electron acceptor in anoxic conditions by biotic or abiotic means (Bryce et al., 2018). N2O is produced as an end product during abiotic nitrate-reducing Fe(II) oxidation (NRFO) (Wang et al., 2019). NO2-, an intermediate product during NO3- reduction by biotic or abiotic means, is chemically very reactive and readily reduced to N2O by abiotic means (Wankel et al., 2017). Studies have shown that Fe(II) minerals such as iron-rich smectites, green rust and siderite are reactive and can enhance abiotic NO2- reduction (Grabb et al., 2017). The occurrence of abiotic NO2- reduction leads to the relative segregation of the lighter and heavy isotopes of N and O (kinetic isotope fractionation, ε) (Chen & MacQuarrie, 2005) providing an effective tool to quantify abiotic NO2- reduction processes. In the light of this, batch experiments were performed to assess the potential of micro-sized siderite to enhance abiotic NO2- reduction in laboratory batch experiments