Low Magnetic Response Research Articles

Local-field effect on the hybrid ferromagnetic-diamagnetic response of opals with Ni nanoparticles

The magnetic properties of artificial opals infiltrated with nickel nanoparticles are studied both experimentally and theoretically. The response of the composite has a dominating ferromagnetic behavior at low magnitude fields (below the saturation region), then it is followed by a dominating diamagnetic one as the intensity of the external applied field is increased. These characteristics are not observed in most cases due to the low magnetic response of the elements involved. Diamagnetism in the artificially synthesized opals was observed, having a negative volume magnetic susceptibility of the order of 10−5. Also theoretical calculations were performed on the basis of the Landau-Lifshitz-Gilbert (LLG) equation, taking into account the diamagnetic response of the host material. Results obtained show the importance of the local magnetic field on the ferromagnetic nanoparticles, as well as the importance of the nature of the magnetic response of SiO2 spheres, which aligns in the opposite direction of the external applied field.

The effect of rare-earth dopants on the texturing of alumina under high-strength magnetic field

The use of magnetic fields in ceramic processing has been of interest recently for tailoring the microstructural grain alignment of ceramics in order to improve mechanical, optical, and other properties. However, a number of challenges exist, including the low magnetic response of most ceramic materials (e.g. alumina), and the lack of low viscosity bulk casting systems available for forming ceramics in a magnetic field. In this work, the low magnetic response of alumina was addressed by adding small amounts (~0.04 atom%) of various rare-earth dopants to phase-pure α-alumina to enhance the response of the bulk material, as supported by previous predictive modeling. After identifying the dopant with the highest magnetic response according to a novel, average facial angle alignment metric, a low-viscosity colloidal casting system, based on a single organic additive was selected to allow for the sintering of formed green bodies. This novel process was used to cast bulk ceramic parts under a magnetic field. The effect of magnetic alignment both in the green state and after sintering was investigated. It was found that both erbium and ytterbium improved the magnetic response of alumina, and that the alignment achieved in the green state was maintained through the sintering process, despite removal from the magnetic field.

Geophysical interpretation of the geology of the Stanthorpe region using aeromagnetic, gravity and radiometric data

This study provides an in-depth geophysical interpretation of the geology of the Stanthorpe region with a particular focus on hydrothermal alteration. The radiometric ternary map outlines the main lithological divisions in the region, which together with Th and Th/K ratio maps distinguish various granitic suites. Magnetic signatures delineate a non-magnetic zone within the low to moderately magnetic Stanthorpe Granite. The non-magnetic section, a north–northwest trending belt with a high density of faults and dykes is interpreted as a hydrothermal alteration zone that is narrower in the north, widens southwards, and is much more extensive at depth than is suggested by the surface alteration pattern. Modelling of gravity data reveals a massive low-density granitic intrusion extending to a depth of 10–15 km. The low-gravity section with modelled rock densities between 2450 and 2670 kg/m3 coincides with the low magnetic susceptibility zone in the magnetic model. High K, low Th and low Th/K also characterise the sections of the Stanthorpe Granite that have both low gravity and magnetic responses. Also conspicuous in the geophysical signatures within the non-magnetic zone is an ovoid feature of low magnetic response, high uranium content with moderate density, interpreted as a granitic pluton. Thus, decrease in magnetisation, changes in K concentration and corresponding low gravity with an associated high density of faults, fractures and dykes in the Stanthorpe region are the main features of the quartz–sericite–chlorite–muscovite hydrothermal alteration.

2, 3-Dimercaptosuccinic Acid-Modified Iron Oxide Clusters for Magnetic Resonance Imaging

Over the last decade, various magnetic nanomaterials have been developed as magnetic resonance imaging (MRI) contrast agents; the greatest challenges encountered for clinical application have been insufficient stability. In this paper, a lyophilization method for 2, 3-dimercaptosuccinic acid-modified iron oxide (γ-Fe2 O3 @DMSA) nanoparticles was developed to simultaneously overcome two disadvantages; these include insufficient stability and low-magnetic response. After lyophilization, the clusters of γ-Fe2 O3 @DMSA with the size of 156.7 ± 15.3 nm were formed, and the stability of the lyophilized powder (γ-Fe2 O3 @DMSA-LP) increased up to over 3 years. It was also found that rehydrated γ-Fe2 O3 @DMSA-LP could be ingested by RAW264.7 cells in very large quantities. Results of pharmacokinetics and biodistribution studies in vivo indicated that γ-Fe2 O3 @DMSA-LP is a promising liver-targeted material. Furthermore, it also exhibited higher MRI efficiency and longer imaging time in the liver than the well-known product Feridex(®) . Moreover, results of vascular irritation and long-term toxicity experiments demonstrated γ-Fe2 O3 @DMSA-LP could be a nontoxic, biocompatible contrast agent in vivo. Therefore, the proposed γ-Fe2 O3 @DMSA-LP can be used as a potential MRI contrast agent in clinic for hepatic diseases.

An integrated mineral exploration programme in the Takengon tenement, Aceh magmatic arc, north Sumatra

A multidisciplinary approach led to the discovery of several gold and base metal occurrences during the 1996–1998 exploration campaign in the Takengon tenement of the Aceh magmatic arc, north Sumatra. Mineralization types included: (i) Au + base metal-bearing quartz veins; (ii) porphyry Cu-style mineralization; (iii) skarn-like Au and Cu-sulphide mineralization; and (iv) granite-hosted molybdenite veins. Regional structural interpretation of synthetic aperture radar and Landsat Thematic Mapper satellite images revealed prominent NNW–SSE and NNE–SSW trending fault zones that cross-cut the region and that were later shown to be spatially related to mineralization. Results from stream sediment analyses delineated several areas that were anomalous in Au±Cu, Pb, Zn, Mo and As, and mineralized bedrock was encountered in some of these areas during a subsequent lithogeochemical survey. An airborne geophysical survey defined a broad region characterized by a low magnetic response with locally high magnetic relief, and moderate to high potassium (K) but low thorium (Th) counts. In addition, the geophysical signals outlined smaller isolated areas that exhibit moderate magnetic anomalies and variable low to high K values. An integrated map with superimposed geological, geochemical and geophysical data demonstrates that results from the various prospecting techniques were generally complementary. Where mineralized and altered rocks occur, the adjacent sediments are metal-bearing (Au±Cu±Pb±As) and the geophysical responses are magnetic, and moderately to highly radioactive (K). In one case in which stream sediments were not auriferous, the discovery of Au- and base-metal-bearing quartz veins was possible through a combined exploration approach consisting of pathfinder elements (As and Pb), elliptical magnetic lineament, moderate to high K anomalies, and regional structures.

Estruturação da seqüência vulcano-sedimentar Rio Mata Cavalo (Morro do Pilar, MG, Brasil) baseada na análise qualitativa de dados geofísicos

Ground geophysics, magnetometry and radiometry have been used to support geological survey of the prospecting area named Bueiro Target, of the Companhia Mineradora de Minas Gerais (COMIG), located southeast from Morro do Pilar, Serra do Espinhaco, Minas Gerais State. The integration of surface geological information and corresponding geophysical data defined four zones, named A, B, C and D. The A Zone, characterized by high magnetic susceptibility and low radiometric values, is composed by itabirites belonging to the Serra da Serpentina Group. The B Zone, part of this Group, is constituted by gray phyllites and meta-siltites, showing low magnetic susceptibility with interruptions in the contour lines, which are interpreted as due to the presence of thrust faults. The C Zone, related to the Rio Mata Cavalo Volcano-Sedimentary Sequence, is characterized by an expressive anomaly of total magnetic field, associated with mafic and ultramafic schists containing several lenses of iron formation and black carbonaceous phyllites; this zone hosts the most important gold geochemical anomalies in the studied area. The D Zone, which corresponds to sheared orthogneisses of the Dona Rita Complex, shows the highest radiometric values of Bueiro Target but has a very low magnetic response.