Magnetic properties of spindle-type iron fine particles obtained from hematite

Spindle-type iron fine particles have been prepared by reduction of silica-coated-hematite particles. Hydrogen reduction of the coated-hematite cores yielded uniform spindle-type iron particles, which were stabilized by surface oxidation. Narrow particle distributions are observed from TEM measurements. X-ray, Mössbauer and magnetization data are in agreement with the presence of nanosized α-Fe particles, having surface layer of spinel structure oxide. Mössbauer spectra show that the oxide surface is superparamagnetic at room temperature. © 2001 Elsevier Science B.V. All rights reserved.

Design studies of the magnetic properties of structural materials affecting the magnetic field of high-homogeneity superconducting magnets

Austenitic stainless steel presents phase changes caused by heat treatment and welding processes. Because it represents a problem in the design of high-homogeneity magnets, we have been studying the magnetic properties of Ti alloys for their use instead of stainless steel as structural material for superconducting magnet construction. In this work, we present the comparative study of the influence of magnetic properties of steel and Ti alloys on the magnetic-field homogeneity of a superconducting coil through numerical calculation using the measured magnetic properties. © 2001 Elsevier Science B.V. All rights reserved.

Magnetic behavior of poly(3-methylthiophene): Metamagnetism and room-temperature weak ferromagnetism

A weak ferromagnetic phase is shown in pressed pellets of partially doped poly(3-methylthiophene) (P3MT) in the whole range from 1.8 to 300 K in magnetic measurements. Thermoremanence data have been used to estimate the suppression of this phase to be around 815 K. We also show that instead of the classical antiferromagnetism for the first-order interaction that gives weak ferromagnetism as a second-order effect, metamagnetic behavior is observed. X-band electron spin resonance (ESR) measurements and magnetization measurements allowed us to estimate that 8.1% of the total number of spins contributes to the weak ferromagnetism at room temperature. The doping level obtained from the ESR data is in good agreement with that estimated from electron dispersive spectroscopy measurements.

Magnetic properties of spinel-type oxides NiMn2-xMexO4

New materials, based on the well-known spinel compound NiMn 2O4, have been synthesized and characterized from the magnetic point of view. The manganese cation was partially substituted in the general formula NiMn2-xMexO4, by nonmagnetic and magnetic elements, such as Me = Ga, Zn, Ni and Cr (0 × 1). Prior to the determination of their magnetic properties, the non-substituted spinel NiMn2O4 was carefully characterized and studied as a function of the oxygen stoichiometry, based on the influence of the annealing atmosphere and quenching rate. The ferrimagnetic character was observed in all samples, with a paramagnetic-to-ferromagnetic transition temperature T c stabilized at 110 K, and well defined long-range antiferromagnetic interactions at lower temperatures, which depend on the applied field and the substitute concentration. © 2006 Sociedad Chilena de Química.

Magnetic images of pharmaceutical dosage forms in the human gastrointestinal tract

Oral administration with solid dosage forms is a common route in the drug therapy widely used. The drug release by the disintegration process occurs in several gastrointestinal tract (GIT) regions. AC Biosusceptometry (ACB) was originally proposal to characterize the disintegration process of tablets in vitro and in the human stomach, through changes in magnetic signals. The aim of this work was to employ a multisensor ACB system to monitoring magnetic tablets and capsules in the human GIT and to obtain the magnetic images of the disintegration process. The ACB showed accuracy to quantify the gastric residence time, the intestinal transit time and the magnetic images allowed to visualize the disintegration of magnetic formulations in the GIT. The ACB is a non-invasive, radiation free technique, completely safe and harmless to the volunteers and had demonstrated potential to evaluate pharmaceutical dosage forms in the human gastrointestinal tract. © 2005 IEEE.

Visualizing the ac magnetic susceptibility of superconducting films via magneto-optical imaging

We have established a link between the global ac response and the local flux distribution of superconducting films by combining magnetic ac susceptibility, dc magnetization, and magneto-optical measurements. The investigated samples are three Nb films: a plain specimen, used as a reference sample, and other two films patterned with square arrays of antidots. At low temperatures and small ac amplitudes of the excitation field, the Meissner screening prevents penetration of flux into the sample. Above a certain ac drive threshold, flux avalanches are triggered during the first cycle of the ac excitation. The subsequent periodic removal, inversion, and rise of flux occurs essentially through the already-created dendrites, giving rise to an ac susceptibility signal weakly dependent on the applied field. The intradendrite flux oscillation is followed, at higher values of the excitation field, by a more drastic process consisting of creation of new dendrites and antidendrites. In this more invasive regime, the ac susceptibility shows a clear field dependence. At higher temperatures a smooth penetration occurs, and the flux profile is characteristic of a critical state. We have also shown that the regime dominated by vortex avalanches can be reliably identified by ac susceptibility measurements. © 2011 American Physical Society.

Electronic structure and magnetic properties of FeWO 4 nanocrystals synthesized by the microwave-hydrothermal method

This communication reports that FeWO 4 nanocrystals were successfully synthesized by the microwave-hydrothermal method at 443 K for 1 h. The structure and shape of these nanocrystals were characterized by X-ray diffraction, Rietveld refinement, and transmission electron microscopy. The experimental results and first principles calculations were combined to explain the electronic structure and magnetic properties. Experimental data were obtained by magnetization measurements for different applied magnetic fields. Theoretical calculations revealed that magnetic properties of FeWO 4 nanocrystals can be assigned to two magnetic orderings with parallel or antiparallel spins in adjacent chains. These factors are crucial to understanding of competition between ferro- and antiferromagnetic behavior. © 2012 Elsevier Inc.

Magnetic characteristics of nanocrystalline GaMnN films deposited by reactive sputtering

The magnetic characteristics of Ga1-xMnxN nanocrystalline films (x = 0.08 and x = 0.18), grown by reactive sputtering onto amorphous silica substrates (a-SiO2), are shown. Further than the dominant paramagnetic-like behaviour, both field- and temperature-dependent magnetization curves presented some particular features indicating the presence of secondary magnetic phases. A simple and qualitative analysis based on the Brillouin function assisted the interpretation of these secondary magnetic contributions, which were tentatively attributed to antiferromagnetic and ferromagnetic phases. © 2012 Elsevier Masson SAS. All rights reserved.

Cation distribution and magnetic characterization of the multiferroic cobalt manganese Co2MnO4 spinel doped with bismuth

The structural and magnetic properties of the cubic spinel oxide Co 2MnO4 (Fd3m space group) doped with different concentrations of bismuth, were investigated by X-ray diffraction and SQUID magnetometry. The Bi3+ ions entering into the CoIII octahedral sites do not alter the effective moment, μeff ∼8.2 μB, whereas both the magnetization M50 kOe at the highest field (50 kOe) and the field-cooled MFC magnetizations increased when increasing the Bi content. The ferrimagnetic character of the parent compound, Co2MnO4, is maintained for all materials although the antiferromagnetic interactions Co2+-Co2+ are affected, resulting in higher values of the Curie-Weiss temperature. Due to the large ionic radius of Bi, octahedra distortions occur as well as valence fluctuations of the Mn ions, giving rise to Jahn-Teller effects and enhancing the exchange interactions. The off-center Bi3+ ion is responsible of non-centrosymmetric charge ordering and should lead to multiferroïsme conditions for the BixCo2-xMnO4 material. © 2012 Elsevier B.V.

Effect of structural anisotropy on electrical and magnetic properties of polyaniline conducting films

It is shown that highly conducting films of polyaniline protonated with di-esters of sulfosuccinic and sulfophthalic acids which contain alkyl- or alkoxy-type substituents exhibit highly anisotropic structural, electrical and magnetic properties. The layered-like structure of these films can be described as consisting of polyaniline chains which are mainly oriented parallel to the plane of the film and form regular out-of-plane stacks. These stacks are separated by bilayers of the dopant anions. Accordingly, the main anisotropy observed for solution cast films implies in-plane and out-of-plane measurements. An electrical anisotropy of about 80 is found for the in-plane and out-of-plane electronic conductivities at 5 K. The temperature dependences of the in-plane and out-of-plane conductivities are qualitatively similar and have been fitted as a series combination of variable-range-hopping-type and power law contributions. A maximum is observed in the temperature dependence of the electrical anisotropy at low temperature. The films also show a clear anisotropy of magnetization whose temperature and field characteristics depend on the chemical structure of the dopant anion. © 2013 Elsevier B.V.

Supramolecular assemblies and magnetic behaviors of the M(II)/p-aminopyridine/malonate (M = Ni, Mn, Cu, Co) systems

The coordination compounds [Ni(μ-mal)(apy)2(H 2O)]·2.8H2O (1), [Mn(μ-mal)(H2O) 2] (2), (apyH)2[Cu(μ-mal)2] (3) and (apyH)2[Co(mal)2(H2O)2] (4) (mal = malonate, apy = p-aminopyridine) have been synthesized and characterized by elemental analysis, vibrational spectroscopy, single crystal X-ray diffraction and magnetometry. With exception of 4, the malonate group acts as bridging ligand leading to the formation of one-dimensional polymeric chains. In compound 1 it was observed the coordination of the p-aminopyridine in the axial positions of the distorted octahedral coordination sphere. The solid-state structure exhibits a high complex 3D network formed by several supramolecular interactions. Magnetic properties were determined for all members of the series and indicate that the materials behave are normal paramagnets, except the Mn polymer 2 which exhibits an antiferromagnetic ground state. © 2013 Elsevier Ltd. All rights reserved.

Intrinsic magnetic properties of BixCo2-xMnO 4 spinels obtained by short-time etching

We report the structural and magnetic properties of Co2MnO 4, partially substituted by Bi at the octahedral site. Bismuth enhances ferromagnetism due to a decrease of the Co2+-Co2+ antiferromagnetic interactions and an increase of the Mn3+-Mn 4+ exchanges. Spurious phases (magnetic and/or nonmagnetic oxides) can easily form because of the large differences between the ionic radii of Bi3+ and Co3+, hiding or altering the intrinsic physical properties of the main BixCo2-xMnO4 phase. An easy way to eliminate the secondary phases is using acid reagents. Short-time etching of Bi0.1Co1.9MnO4 using nitric acid was successfully used, keeping most of the properties of the initial compound, with no alteration of the crystallographic structure. Final stoichiometry was respected (∼Bi0.08Co1.82MnO4), meaning that the material after etching definitely contains bismuth elements in its structure and the observed properties are intrinsic to the oxide spinel. Additional experiments were performed as a function of the synthesis conditions, showing that an optimal pH value of 7 allowed the best magnetic response of the non-doped material. © 2013 Elsevier B.V. All rights reserved.

Chromosomal imbalances in successive moments of human bladder urothelial carcinoma

Objective: To understand developmental characteristics of urinary bladder carcinomas (UBC) by evaluating genomic alterations and p53 protein expression in primary tumors, their recurrences, and in the morphologically normal urothelium of UBC patients. Methods: Tumors and their respective recurrences, six low-grade and five high-grade cases, provided 19 samples that were submitted to laser microdissection capture followed by high resolution comparative genomic hybridization (HR-CGH). HR-CGH profiles went through two different analyses-all tumors combined or classified according to their respective histologic grades. In a supplementary analysis, 124 primary urothelial tumors, their recurrences, and normal urothelium biopsied during the period between tumor surgical resection and recurrence, were submitted to immunohistochemical analyses of the p53 protein. During the follow-up of at least 21 patients, urinary bladder washes citologically negative for neoplastic cells were submitted to fluorescence in situ hybridization (FISH) to detect copy number alterations in centromeres 7, 17, and 9p21 region. Results and Conclusions: HR-CGH indicated high frequencies (80%) of gains in 11p12 and losses in 16p12, in line with suggestions that these chromosome regions contain genes critical for urinary bladder carcinogenesis. Within a same patient, tumors and their respective recurrences showed common genomic losses and gains, which implies that the genomic profile acquired by primary tumors was relatively stable. There were exclusive genomic alterations in low and in high grade tumors. Genes mapped in these regions should be investigated on their involvement in the urinary bladder carcinogenesis. Successive tumors from same patient did not present similar levels of protein p53 expression; however, when cases were grouped according to tumor histologic grades, p53 expression was directly proportional to tumor grades. Biopsies taken during the follow-up of patients with history of previously resected UBC revealed that 5/15 patients with no histologic alterations had more than 25% of urothelial cells expressing the p53 protein, suggesting that the apparently normal urothelium was genomically unstable. No numerical alterations of the chromosomes 7, 17, and 9p21 region were found by FISH during the periods free-of-neoplasia. Our data are informative for further studies to better understand urinary bladder urothelial carcinogenesis. © 2013 Elsevier Inc.

Influence of current density on crystalline structure and magnetic properties of electrodeposited Co-rich CoNiW alloys

The influence of current density, at the interval 5-100 mA cm-2, on the structural and magnetic properties of electrodeposited (Co 100-xNix)100-yWy alloys (x = 23-33.5 at. % Ni, y = 1.7-7.3 at. % W) was studied from a glycine-containing bath. W-content decreases with the increase of the current density magnitude. X-ray data have shown stabilization of hexagonal close packed, face centered cubic or a mixture of these structures by modulating the applied cathodic current density, for values lower than 50 mA cm-2. Two structural phase transitions were observed: one from hexagonal close packed to face centered cubic structural transition occurring for a current density of 20 mA cm -2, and another one, from cubic crystalline phase to amorphous state, which happens for values higher than 50 mA cm-2. These structural phase transitions seem to be associated with the W-content as well as average crystalline grain sizes that reduce with increasing the current density value. The grain size effect may explain the face centered cubic stabilization in Co-rich CoNiW alloys, which was initially assumed to be basically due to H-adsorption/incorporation. Magnetic properties of Co-rich CoNiW alloys are strongly modified by the current density value; as a result of the changes on the W-content and their structural properties© 2013 Elsevier B.V. All rights reserved.