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Summary  

The thermal decomposition of manganese tris(malonato)ferrate(III) hexahydrate, Mn3[Fe(CH2C2O4)3]2 . 6H2O has been investigated from ambient temperature to 600 °C in static air atmosphere using various physico-chemical techniques, i.e., simultaneous TG-DTG-DSC, XRD, Mössbauer and IR spectroscopic techniques. Nano-particles of manganese ferrite, MnFe2O4, have been obtained as a result of solid-state reaction between a-Fe2O3 and MnO (intermediate species formed during thermolysis) at a temperature much lower than that for ceramic method. SEM analysis of final thermolysis product reveals the formation of monodisperse manganese ferrite nanoparticles with an average particle size of 35 nm. Magnetic studies show that these particles have a saturation magnetization of 1861G and Curie temperature of 300 °C. Lower magnitude of these parameters as compared to the bulk values is attributed to their smaller particle size.

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Nanoscale spinel ferrites prepared by mechanochemical route

Thermal stability and size dependent magnetic properties

Journal of Thermal Analysis and Calorimetry
Authors: V. Šepelák, P. Heitjans, and K. Becker

Abstract  

Among the many types of preparation and processing techniques, the nonconventional mechanochemical route has been recognized as a powerful method for the production of novel, high-performance, and low-cost nanomaterials. Because of their small constituent sizes and disordered structural state, nanoscale materials prepared by mechanochemical route are inherently unstable with respect to structural changes at elevated temperatures. Taking into account the considerable relevance of the thermal stability of nanoscale complex oxides to nanoscience and nanotechnology, in the present work, results on the response of mechanochemically prepared MgFe2O4 and NiFe2O4 to changes in temperature will be presented. Several interesting features are involved in the work, e.g., a relaxation of the mechanically induced cation distribution towards its equilibrium configuration, a disappearance of the superparamagnetism on heating, an increase of both the saturation magnetization and the Néel temperature with increasing particle size, and a core-shell structure of nanoparticles.

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Abstract  

Manganese zinc ferrous fumarato–hydrazinate precursor, Mn0.6Zn0.4Fe2(C4H2O4)3·6N2H4 was synthesized for the first time and characterized by chemical analysis, infrared spectral studies, and thermal analysis. Infrared studies show band at 977 cm−1 indicating bidentate bridging nature of the hydrazine in the complex. Thermogravimetric (TG) studies show two steps dehydrazination followed by two steps total decarboxylation. The precursor on touching with burning splinter undergoes self propagating autocatalytic decomposition yielding ultrafine Mn0.6Zn0.4Fe2O4. XRD studies confirms single phase formation as well as nanosize nature of “as prepared” Mn0.6Zn0.4Fe2O4. The saturation magnetization of the “as prepared” Mn0.6Zn0.4Fe2O4 was found to be 31.46 emu gm−1, which is lower than the reported, confirms the ultrafine nature of the oxide.

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In this study we interpret the magnetic anomalies at satellite altitude over a part of Europe and the Pannonian Basin. These anomalies are derived from the total magnetic measurements from the CHAMP satellite. The anomalies are reduced to an elevation of 324 km. An inversion method is used to interpret the total magnetic anomalies over the Pannonian Basin. A three dimensional triangular model is used in the inversion. Two parameter distributions, Laplacian and Gaussian are investigated. The regularized inversion is numerically calculated with the Simplex and Simulated Annealing methods and the anomalous source is located in the upper crust. A probable source of the magnetization is due to the exsolution of the hematite-ilmenite minerals.

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Abstract  

A method has been developed enabling the direct coupling of first or second antibody to finely dispersed magnetite (Fe3O4). The immunosorbent thus produced was applied in various radioimmunoassay systems (T3, T4, TSH, Cortisol) for the separation of bound and free antigens. The elimination of the need for precoating the magnetic particles with a polymer has several advantages. One of them lies in the ease of one-step production of the immunosorbent and other is the high antibody/magnetite ratio. The influence of the concentration of the immunosorbent and detergent (TWEEN 20 or TRITON X-100) on the assay parameters (Bo, NSB, etc.) has been systematically investigated and the optimum concentration of the magnetizable particles and detergent has been determined. The reliability of magnetic separation has been validated by comparing it with the conventional PEG separation method.

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Abstract  

Thermal decomposition of cobalt hexa(formato)ferrate(III) decahydrate, Co3[Fe(HCOO)6]2. 10H2O, has been studied up to 973 K in static air atmosphere, employing TG, DTG, DSC, XRD, ESR, Mössbauer and infrared spectroscopic techniques. Dehydration occurs in two stages in the temperature range of 340–430 K. Immediately after the removal of the last water molecule the anhydrous complex undergoes decomposition till -Fe2O3 and cobalt carbonate are formed at 588 K. In the final stage of remixing of cations, a solid state reaction between -Fe2O3 and cobalt carbonate leads to the formation of CoFe2O4 at a temperature (953 K) much lower than for the ceramic method. A saturation magnetization value of 2310 Gauss of ferrite (CoFe2O4) shows its potential to function at high frequencies.

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Abstract

Four paleosol layers indicating wet and moderate periods and five loess layers indicating dry and cold climate were separated by different methods. The following climate cycle model, based on the development of the sediment sequence created by the influence of climatic, geologic and geomorphologic phenomena, was established by detailed paleomagnetic studies (e.g. anisotropy of magnetic susceptibility (AMS), isothermal remanent magnetization (IRM), frequency dependence of magnetic susceptibility (κFD), etc.):

  1. A well-foliated magnetic fabric predominantly built up by multi-domain ferromagnetic minerals (magnetite, maghemite) was developed during the semi-arid (350–400 mm/y) and cold loessification period of the Pleistocene. The magnetic fabric can reflect the direction of dust deposition and/or the paleoslope.
  2. The accumulation period of dust was followed by the more humid (650 mm/y) pedogenic period indicated by the enrichment of superparamagnetic minerals and by the disturbed or inverse magnetic fabric developed during pedogenesis by different processes (e.g. leaching and/or bioturbation).
  3. The third period following the pedogenic period is the humid erosional phase indicated by the finely layered reworked loess. The magnetic fabric built up by multi-domain ferro- and superparamagnetic minerals is characterized by better-aligned directions of principal susceptibilities than in the wind blown material. Sheet wash and other waterlogged surface processes appeared in the fabric of these layers. This process is possibly connected to sudden, rare yet significant events with high precipitation and absence of vegetation.
  4. The cycle was closed by the beginning of the next dust accumulation period.
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At the Permian/Triassic boundary, terrestrial as well as marine life was seriously decimated. The drastic reduction was possibly due to a global event. In order to demonstrate this, sections at great distance from one another need to be correlated, which is a difficult task, especially between marine and land sections. One of the methods, which is independent of the environment, is magnetostratigraphic correlation. It was intended to apply this method for precise dating to Permian/Triassic boundary sections from the Bükk Mts, which include strata with high concentrations of magnetospherules. Since the Paleozoic-Mesozoic rocks of the Bükk Mts are anchimetamorphosed and intensively tectonized, it was decided to carry out a pilot paleomagnetic study on samples from two sections with different dips, before collecting a large number of samples for the intended magnetostratigraphy survey. The results of this study can be summarized as follows. The rocks of the sections possess remanences of pre-tilting age, and the magnetic fabric does not show any evidence of strong deformation. Nonetheless, the magnetization can not be primary since the measured inclinations are far too steep for the Permian/Triassic boundary. The estimated age of the acquisition of the paleomagnetic signal is Late Cretaceous. Although the results are negative in terms of magnetostratigraphy, they deserve attention from a tectonic point of view. The observations suggest that either the studied localities or the entire range of the Bükk Mts was involved in a post-Cretaceous (but pre-Miocene) counterclockwise rotation of about 40°

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Abstract  

Nickel ferrite is technologically important magnetic material extensively used in high frequency applications such as microwave device due to its high resistivity and sufficiently low losses. It also finds application in the ferrofluids technology. Therefore, ultrafine nickel ferrite was prepared by autocatalytic combustion of novel nickel ferrous fumarato-hydrazinate precursor. The precursor was characterized by IR, AAS, TG and DTA, and a chemical formula of NiFe2(C4H2O4)3·6N2H4 was fixed. This precursor once ignited with a burning splinter at room temperature, glows and the glow spreads over the entire bulk completing the autocatalytic combustion of the precursor to ultrafine ferrite. The single phase formation of ultrafine nickel ferrite was confirmed by XRD, IR spectra and TEM. The average particle size of the ultrafine ferrite was found to be ∼20 nm by TEM. The observed lower value of saturation magnetization for nickel ferrite was due to the superparamagnetic nature of the particles, which increased with the increasing sintering temperature. The ultrafine nickel ferrite was then sintered at 1000°C for 5 h and was characterized by XRD, IR spectra, SEM and TEM. The variation of resistivity, Seebeck coefficient and a.c. susceptibility as a function of temperature was measured for NiFe2O4 and the results are discussed.

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Summary  

A simple, one step, inclusive immunoradiometric assay for human chorionic gonadotropin (hCG) employing monoclonal antibodies is described. Commercially available monoclonal antibodies from various commercial sources were screened. Identified “detection” antibody was radiolabeled with 125I and the selected “capture” antibody was chemically coupled to magnetizable cellulose to form a solid phase. In the procedure developed, standard/sample, radiolabeled antibody and capture antibody were incubated together for 3 hours at room temperature with shaking. After incubation, the bound complex was quantitated for the associated radioactivity. The analytical sensitivity observed was 1.0 mIU/ml with a wide concentration range up to 1000 mIU/ml of hCG. “High dose hook” of the developed assay was observed beyond 2000 mIU/ml. Results showed that the developed assay had a good precision: intra-assay CV less than 8%, inter-assay CV less than 10% and good analytical recovery of 97-109%. The clinical samples analyzed by the developed procedure showed a good correlation with that of the commercial kit (r = 0.92; y = 0.99x+0.51).

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