Application Of Magnetic Materials Research Articles

Synthesis of Hematite (α-Fe2O3) Nanorods: Diameter-Size and Shape Effects on Their Applications in Magnetism, Lithium Ion Battery, and Gas Sensors

We demonstrated in this paper the shape-controlled synthesis of hematite (alpha-Fe(2)O(3)) nanostructures with a gradient in the diameters (from less than 20 nm to larger than 300 nm) and surface areas (from 5.9 to 52.3 m(2)/g) through an improved synthetic strategy by adopting a high concentration of inorganic salts and high temperature in the synthesis systems to influence the final products of hematite nanostructures. The benefits of the present work also stem from the first report on the <20-nm-diameter and porous hematite nanorods, as well as a new facile strategy to the less-than-20-nm nanorods, because the less-than-20-nm diameter size meets the vital size domain for magnetization properties in hematite. Note that the porous and nonporous hematite one-dimensional nanostructures with diameter gradients give us the first opportunity to investigate the Morin temperature evolution of nanorod diameter and porosity. Evidently, the magnetic properties for nanorods exhibit differences compared with those for the spherical particle counterparts. Hematite nanorods are strongly dependent on their diameter size and porosity, where the magnetization is not sensitive to the size evolution from submicron particles to the 60-90 nm nanorods, while the magnetic properties change significantly in the case of <20 nm. In other words, for the magnetic properties of nanorods, in a comparable size range, the porous existence could also influence the magnetic behavior. Moreover, applications in formaldehyde (HCHO) gas sensors and lithium batteries for the hematite nanostructures with the diameter/surface area gradient reveal that the performance of electrochemical and gas-sensor properties strongly depends on the diameter size and Brunauer-Emmett-Teller (BET) surface areas, which is consistent with the crystalline point of view. Thus, this work not only provides the first example of the fabrication of hematite nanostructure sensors for detecting HCHO gas, but also reveals that the surface area or diameter size of hematite nanorods can also influence the lithium intercalation performances. These results give us a guideline for the study of the size-dependent properties for functional materials as well as further applications for magnetic materials, lithium-ion batteries, and gas sensors.

Organic and Molecular Magnets

AbstractFor Abstract see ChemInform Abstract in Full Text.

Spray pyrolysis deposition of zinc ferrite films from metal nitrates solutions

Well-crystallized spinel ZnFe2O4 thin films with good adhesion have been successfully prepared on glass substrates heated above 350°C by a spray pyrolysis deposition from mixed zinc and iron nitrates aqueous solutions. The solution pH has an influence on the surface morphology of ZnFe2O4 films. A smooth and dense surface was obtained from the mixed solution with a pH of 2.0, while a rough and inhomogeneous surface could be observed from the solution with a pH of 8.0. The crystallite size of ZnFe2O4 films was found to be small, ranging from 10 to 21 nm as calculated from X-ray diffraction patterns, which is of interest for magnetic material applications. The indirect and direct band gap energies of the sprayed films were estimated to be 1.78 and 2.70 eV, respectively. A schematic illustration is proposed to show the possible deposition processes of ZnFe2O4 thin films by spray pyrolysis.

Characterization of electrodeposited thin layers of magnetic alloys by Mössbauer spectroscopy

Rare earth and transition metal alloys are interesting magnetic materials for applications in the field of magnetooptical memories. We describe the preparation of Dy/Fe alloys by electrodeposition using a pulsed galvanostatic process. Samples were characterized by Mossbauer spectroscopy. Thin layers obtained with short electrolysis pulses (0.1 s) give a Mossbauer spectrum analysed as the sum of two subspectra: the first corresponds to a spectrum originating from very small sized particles of Fe and the second is attributed to a Dy/Fe phase. Longer electrolysis pulses (1 s) give samples whose spectrum is also the sum of two subspectra: the first is attributed to metallic Fe with an extended particle-size distribution while the second is attributed to a Fe/Dy alloy. Mossbauer spectroscopy was found useful in determining the best electrolysis parameters leading to domains of uniform magnetization with high coercive fields.

Air Force Application of Advanced Magnetic Materials

ABSTRACTA national initiative is underway to develop and test a more electric aircraft (MEA) and is being led by the U.S. Air Force Research Laboratory at Wright-Patterson Air Force Base, Ohio. The MEA concept is based on utilizing electric power to drive aircraft subsystems which are currently driven by a combination of hydraulic, pneumatic, electric and mechanical power transfer systems. A major objective of this effort is to increase military aircraft reliability, maintainability and supportability and to drastically reduce the need for ground support equipment. These improvements will be realized through the further advancement of key MEA technologies, including magnetic bearings, aircraft integrated power units (IPU), and starter/generators (IS/G) internal to an aircraft main propulsion engine. These advanced developments, as well as weapon and space power applications, are the driving force for the new emphasis on high temperature and high strength magnetic materials for power applications. In determining the best magnetic material for an application it is typically necessary to conduct an engineering trade-off analysis which takes into consideration mechanical behavior, electrical loss, and magnetic properties under the conditions of actual usage. New materials solutions are required to meet these challenges, as designers often find the magnetic material performance to be the technological limitation.

Effect of sample preparation on the magnetic and magnetocaloric properties of amorphous Gd70Ni30

Certain applications of magnetic materials require the knowledge of the magnetocaloric effects, i.e., the adiabatic change of temperature or the isothermal change of the entropy upon application or removal of magnetic field. While the isothermal magnetic entropy change can be calculated from magnetic data only, the calculation of the adiabatic temperature change requires the knowledge of the field-dependent specific heat as well. To compare magnetocaloric effect results obtained from magnetic-only, thermal-only, or combined methods requires the evaluation of the mutual reliability of all methods. In crystalline materials it usually does not present a problem to perform thermal and magnetic measurements on the same sample or at least on samples of identical state. For amorphous materials, unfortunately, thermal measurements are extremely difficult to perform on the ribbons themselves so usually pellets pressed from powdered ribbons, with silver as a binder, are applied. After the magnetic entropy change calculated from thermal measurements performed on such a composite did not agree with the data obtained from magnetic measurements performed on the original ribbon, magnetic measurements were carried out on the pellet and its predecessor powders. Comparison of the results revealed that the pellet’s properties do not reflect the properties of the original ribbon. However, comparison of magnetic and thermal measurements carried out on the pellet itself show good agreement if proper numerical methods are used for evaluation. The study concludes that amorphous ribbons are far more competitive for certain applications than the thermal measurements, performed on the pellet only, would indicate.

Molecular characterization of a carbamoyl-phosphate synthetase II (CPS II) gene from Leishmania mexicana

Magnetic materials have been widely used in bioseparation in recent years due to their good biocompatibility, magnetic properties, and high binding capacity. In this review, we provide a brief introduction on the preparation and bioseparation applications of magnetic materials including the synthesis and surface modification of magnetic nanoparticles as well as the preparation and applications of magnetic nanocomposites in the separation of proteins, peptides, cells, exosomes and blood. The current limitations and remaining challenges in the fabrication process of magnetic materials for bioseparation will be also detailed.

有機金属化合物の加圧熱分解による機能性炭素材料の合成

Carbon composites of controlled morphology dispersed with finely metal or metallic compound particles can be synthesized in high carbon yield by the pressure pyrolysis of organometallic polymers. The size and the morphology of the carbon matrix can be controlled by the selection of the pyrolysis conditions as well as the amounts of coexistent water and the metal concentration in copolymers. Organometallic polymers undergo pressure pyrolysis affording the liquid phase of oligomers, which is responsible for the morphology of carbons through liquid-liquid microphase separation. Supercritical water affected the liquid phase separation during pyrolysis yielding carbon spherulite of about several micrometers dispersed with ferrite particles less than 100 nm. The magnetic properties of metal-dispersed carbon are attributed to the crystallinity and the particle size of the metals, which have been foundto depend strongly on the properties of both the carbon-metal bond of organometallic compounds and the carbon-carbon bond of the polymer matrix. Metal-dispersed carbon composites of controlled morpholgy have potentials of many applications for magnetic materials, catalysts and pigments and so on. This processing affords a novel method for producing carbon nano-composites with controlled microstructure and morphology.

HREM study of M, Y and W hexagonal type ferrites

Hexagonal ferrites have similar structural symmetries and are built by the same structural units. HREM has proved to be an excellent tool to identify individual stacking bloks, in M, Y and W hexaferrites.M, Y and W hexagonal type ferrites are well-known magnetic materials for applications. Some previous electron microscopy studies on these ferrites, reveal a variety of new phases coming from the microsyntactic intergrowth of M, Y and W structures. We report in this paper some microstructural features of these ferrites.BaFe12O19 (M) hexagonal ferrite was synthetized by using the standard ceramic technique. Crystals of Y type ferrite (nominal composition: BaLi0.5Fe0.5ZnFe16027) were prepared from stoichiometric amounts of BaCO3, ZnO and LiCO3. The synthesis of W-type ferrite (formula: Ba2Zn2Fe16027) is described elsewhere.Samples for observation were prepared by grinding powders of the above ferrites under acetone. HREM study was performed at the "Centro de Microscopía Electrónica, Univ. Complutense" using both 400 Kv and 200 Kv electron microscopes (JEM-400EX and JEM-200FX)

Magnetism: Intermag '83

The Intermag conference is probably the most important and certainly the most comprehensive annual meeting devoted to applied magnetism and the application of magnetic materials. It is organised by the Magnetics Society of the IEEE and is sponsored by major US and some Japanese and European firms.

New magnetic materials

The use of magnetic materials in all forms of electrical and electronic engineering means that there is a continuous research and development interest in improving the method of utilisation and expanding the applications of existing materials. There is also never ending work, generally industrially based, on improving the methods of manufacturing existing magnetic materials and the techniques of fabricating these materials into devices. In contrast, the successful development of a new magnetic material occurs less regularly, but often has a larger impact on the commercial applications of magnetic materials than any programme of work on existing materials

Magnetization, anomalous barkhausen effect, and core loss of supermendur under high temperature cycling

The magnetization and core loss of Supermendur were measured up to 900°C under conditions of slow temperature cycling in vacuum. As a consequence of this heating the coercivity at 25°C increased from 21 A/m to about 110 A/m. This increase is less than previously reported. A prominent anomalous Barkhausen effect, pinched-in hysteresis loops, and a magnetic viscosity field in excess of 20 A/m were observed in the range 600 to 700°C. At 850°C Super-mendur had a coercivity of 23 A/m, a saturation induction exceeding 1.5 T, a core loss of 26 W/kg at 400 Hz, and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B_{\max}</tex> of 1.5 T. Super-mendur may be useful for high temperature soft magnetic material applications where some history dependence of properties and instability of minor loops at lower temperatures is acceptable.

Magnetism in Medicine

The applications of magnetic materials and magnetic fields in medicine are reviewed. Direct biological effects of magnetic fields, clinical uses of the mechanical force exerted by magnets, and magnetic analysis as a tool in biochemistry are considered. The authors' applications of the technology of fine particle iron to the treatment of cancer and mental disease, for investigation of basic biochemistry and for diagnostic purposes are discussed. A significant step in these applications has been the discovery of sublingual assimilation of fine particle iron.

Application of Magnetic Materials

An examination of some of the applications of magnetic materials from the standpoint of the metallurgical technology that has made these applications possible.

A symposium on magnetism - London, September, 1955

The Electronics Group of The Institute of Physics held an informal symposium on recent developments in magnetism on 23 and 24 September, 1955. Speakers from university, government and industrial research groups took part in the conference and the subjects discussed ranged from some latest advances in theoretical studies, to the application of magnetic materials to computor systems.