bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sol-Gel Chemistry by Ring-Opening Polymerization
Authors: Rahimian Kamyar , Loy Douglas A. 
Published: April 2011

ABSTRACTSol-gel processing of materials is plagued by shrinkage during polymerization of the alkoxide monomers and processing (aging and drying) of the resulting gels. We have developed a new class of hybrid organic-inorganic materials based on the solventless ring-opening polymerization (ROP) of monomers bearing the 2,2,5,5-tetramethyl-2,5-disilaoxacyclopentyl group, which permits us to drastically reduce shrinkage in sol-gel processed materials. Because the monomers are polymerized through a chain growth mechanism catalyzed by base rather than the step growth mechanism normally used in sol-gel systems, hydrolysis and condensation products are entirely eliminated. Furthermore, since water is not required for hydrolysis, an alcohol solvent is not necessary. Monomers with two disilaoxacyclopentyl groups, separated by a rigid phenylene group or a more flexible alkylene group, were prepared through disilylation of the corresponding diacetylenes, followed by ring closure and hydrogenation. Anionic polymerization of these materials, either neat or with 2,2,5,5-tetramethyl-2,5-disila-1-oxacyclopentane as a copolymer, affords thermally stable transparent gels with no visible shrinkage. These materials provide an easy route to the introduction of sol-gel type materials in encapsulation of microelectronics, which we have successfully demonstrated.
Isotropic and Anisotropic Nd-Fe-B Magnet Developments
Authors: Panchanathan V. 
Published: April 2011

ABSTRACTThis paper deals with the magnetic and technological properties of isotropic Nd-Fe-B magnets over a wide range of Nd and B contents. They can be used to determine the optimum composition based on requirements. In anisotropic magnets, Nd and B ranges for production of high energy product rings was determined in Nd-Fe-Co-Ga-B system. This is also used in production.
Micromagnetics of Nanocrystalline Permanent Magnets
Authors: Schrefl T. , Fidler J. 
Published: April 2011

ABSTRACTMicromagnetic finite element calculations provide the theoretical limits for the remanence, the coercive field, and the coercive squareness of nanocomposite Nd2Fe14B/α-Fe,Fe3B,Fe23B6magnets. The influence of the intrinsic magnetic properties and the microstructure were investigated using an energy minimization technique. The coercive field reaches a maximum as a function of the average grain size at about 15 nm - 20 nm. The replacement of α-Fe with Fe3B improves the coercive field but deteriorates the loop shape. The reduction of the magnetization and the exchange constant in the soft magnetic Fe3B phase by 20% improves the coercive field without a significant loss in the remanence. An increase of the hard phase anisotropy by 8% enhances the coercive field by more the 100 kA/m in two-phase α-Fe/Nd2Fe14B and by 60 kA/m in two-phase Fe3B/Nd2Fe14B magnets. Dynamic simulations for magnetostatically interacting particles of a bonded magnet show a slight influence of the particle arrangement on magnetization reversal. The interaction field in the range of 100 kA/m to 200 kA/m rapidly decreases the distance from the particle.
Analysis of Magnetization Processes in Nanocomposite Hard Magnetic Materials from Macroscopic Magnetic Measurements and X-RAY Magnetic Circular Dichroism
Authors: David Stéphane , Mackay Kenneth , Bonfim Marlio , Pizzii Stefania , Fontaine Alain , Givord Dominique 
Published: April 2011

ABSTRACTA series of RExTMbalBy (3≤x≤5.5, 15≤y≤25 at%) nanocomposite magnets were prepared using the classical method of alloy rapid quenching and subsequent devitrification. Appropriate elemental additions and substitutions allowed the technical magnetic properties to be optimized. The analysis of the both hysteresis cycles and static susceptibility measurements in the range 20K-300K reveals that magnetization reversal in these materials can be interpreted schematically as a two-step process : the initial magnetization reversal is dominated by reversible processes while irreversible processes, which characterize the coercivity mechanism, occur at larger field values. To complement this study, X-Ray Magnetic Circular Dichroism (XMCD) spectroscopy was applied as an element-selective probe of magnetization reversal in nanocomposite samples. This allowed the hysteresis cycles of both hard and soft phases to be separated from the total cycle. Magnetization processes in these bulk heterogeneous systems are discussed in the light of information brought by the complementary applied experimental techniques.
Residual Amorphous Phase in a Fe/NdFeB Nanoconipositie Hard Magnets
Authors: Hamano M. , Yamasaki M. , Mizuguchi H. , Kobayashi T. , Yamamoto H. , Inoue A. 
Published: April 2011

ABSTRACTA residual amorphous phase can be observed when Nd content is less than 8 at% in a a Fe/NdFeB nanocomposite with various additional elements which was prepared by melt-spinning and heat treatment. The surface velocity of the single-roller melt-spinner for optimal coercive force (Hcj) was 10-15 m/s. By adding Nb, Hcj increases monotonically. Nearly homogeneous crystal size of around 5 nm is observed in a sample composition of NdxFex Cox Nb2,B2 With Nd=8 at%, the maximum Hcj is as large as 575kA/m (7.22kOe) at Nb=2.5 at%, and the best (BH)max is 154kJ/m3 (19.4MGOe) at Nb=0.5 at% in optimally heat-treated and pulse-current magnetized samples. By high-resolution transmission electron microscopy, a residual amorphous phase is observed in all alloy ribbons with Nd=8 at%, which shows soft magnetic properties and is thought to act as a crystal growth inhibitor. To estimate the existing ratio of the amorphous phase and crystallized phases, the Mössbauer effect has been studied. It was found that the ratio of the crystallized Nd2Fe14B1 phase increases with increasing Nb content and that several wt% of the residual amorphous phase is certified. Epoxy-resin bonded magnets were prepared by compression molding, and revealed that, comparing to the MQP bonded magnet using conventional MQP-B powder, their (BH)max are in the same order of 72kJ/m3 (9MGOe), and magnetization at lower magnetic field than 800kA/m (10kOe) is superior. Initial flux loss at 100°C for 1.8ks, however, is in the range of 3-8% depending on Nb contents.
Magnetization and Interactions of Single Domain Sm2Co17 Particles Embedded in CaO Matrix
Authors: Liu Wenge , Mccormick Paul G. 
Published: April 2011

ABSTRACTInvestigation of the interactions in two magnetic composite systems composed of ∼8 vol% isolated Sm2Co17 nanoparticles of different size ranges in a CaO matrix has been made by comparing the isothermal remanent magnetization curves (IRM) with the dc demagnetization curves (DCD) using Wohlfarth remanence relation. The presence of a weak demagnetizing field was evidenced in the sample with smaller magnetic particles (7-90nm), indicating the magnetostatic interaction between the magnetic particles was dominant in this sample. The large positive deviation from Wolhfarth relation in the sample with larger particles (10-250nm) suggests the presence of multigrain particles in which neighboring grains interact strongly with each other. The hysteresis curves of the two composite systems were measured at temperatures between 5 and 350K. A nearly linear temperature dependence of the coercivity was observed in both samples up to 350 K. From these results it is shown that although the sizes of the Sm2Co17 particles are well below the critical size for single domain particle, there is no evidence that the magnetization reversals in these particles are coherent rotation.
Microstructural Investigation of RE3(Fe.V) 29 (RE = Nd, Tb) Magnetic Materials
Authors: Bernardi J. , Noner M. , Fidler J. , Han X.F. , Yang F.M. 
Published: April 2011

ABSTRACTThe microstructure of V stabilized RE3(Fe,V)29 (RE=Nd,Tb) has been investigated by transmission electron microscopy (TEM). The investigated samples were prepared by arc melting and subsequent annealing above 910°C. X-ray diffraction confirms that the samples can be indexed based on a monoclinic Nd3(Fe,Ti)29-type structure (3:29) with A2/m space group. Our TEM investigation confirms that Nd3(Fe,V)29 contains usually grains with 3:29 structure and A 2/m space group. In addition grains with rhombohedral Th2Zn17 structure are observed regularly. The Tb3(FeV)29 alloy consists also of grains with monoclinic Nd3(Fe,Ti)29-type structure and contains a high density of planer defects like crystallographic twins or antiphase boundaries. Twinning occurs preferably on (402) of the monoclinic 3:29 structure. No tetragonal RE(Fe,V)12 phase or Fe is found.
Chemical Ordering and Microstructural Affects on Magnetic Properties of Sm2Fe17 and Sm2Fe17Nx
Authors: Meacham B.E. , Dennis K.W. , Mccallum R.W. , Shield J.E. 
Published: April 2011

ABSTRACTThe effect of chemical order and defect structure on the magnetization process in Sm2Fe17 and Sm2Fe17Nx has been investigated. In Sm2Fe17, chemical disorder results in the development of random anisotropy and a small degree of magnetic hardness. The anisotropy is reduced as long-range order increases. The motion of domain walls in Sm2Fe17Nx is more dependent on the antiphase domain structure than on the amount of long-range order.
Permanent Magnetism in Exchange-Coupled Nanocomposites
Authors: Skomski R. , Liu J. P. , Sellmyer D.J. 
Published: April 2011

ABSTRACTThe magnetic properties of permanent magnetic nanocomposites are investigated both experimentally and by model calculations. Rare-earth transition-metal films and nanocomposite thin films containing a L10hard phase (PtFe) have been prepared by plasma sputtering and heat treatment. By choosing suitable heat-treatment processes a nearly ideal nanostructure and high energy products of up to about 50 MGOe have been achieved for the Fe-Pt system. The behavior of the nanocomposites is discussed in terms of a model applicable to nearly ideal magnets, where there are no pronounced shoulders in the hysteresis loops. Analytic expressions for M(H) are obtained for a number of cases, and it is discussed how the loops depend on the micromagnetic parameters of the involved phases. A novel aspect of magnetic nanostructures is that very small magnetic grains exhibit very large energy products, even if they are intrinsically soft-magnetic.
The Influence of Microstructure on the Magnetic Properties in Nanostructured Copt L10Thin Films
Authors: Jeong S. , Mchenry M.E. , Laughlin D.E. 
Published: April 2011

ABSTRACTWe have applied the Neel's spin pair potential model to model the dependence of magnetocrystalline anisotropy on the long range order parameter. We have produced CoPt nanoscale thin films, with and without an immiscible second phase, by RF and DC magnetron sputtering. These thin films showed a shoulder in their magnetic hysteresis, indicative of a disordered soft magnetic phase for samples annealed above 600 °C while it was barely detectable in 500-600 °C annealed samples. A (111) texture is observed in as-deposited and annealed films is identified as one of the possible contributions to the lower coercivity squareness S* and perpendicular magnetic properties. Micromagnetic calculations confirmed a poor exchange interaction, identified rotational energy barriers and inferred that the ordered region was not fully ordered. The initial stage of ordering clearly showed a discontinuous type transformation.
Chemical Characterization of Magnetic Materials at High Spatial Resolution
Authors: Scott John Henry J. 
Published: April 2011

ABSTRACTThe fabrication of nanoscale magnetic materials and novel heterostructures has placed great demands on the analytical tools used to characterize the chemical and structural variations in these samples. Attempts to determine the composition, phase, crystallinity, and interface structure of nanoscale materials often involve tradeoffs between accuracy, sensitivity, and spatial resolution. Traditional techniques such as electron energy-loss spectroscopy (EELS), energy dispersive x-ray spectrometry (EDS), secondary ion mass spectrometry (SIMS), and scanning Auger microscopy (SAM) will be surveyed in this context. Powerful new tools for probing the chemical heterogeneity of materials at ultrafine length scales will also be discussed, including energy-filtered transmission electron microscopy (EFTEM) and spectrum imaging, as well as recent advances in new methods such as backscattered electron Kikuchi patterns (BEKP) and microcalorimetry.
Giant Magnetoresistance of Electrostatic Self-Assembled Fe3O4Nanocluster and Polymer Thin-Films
Authors: Liu Yanjing , Claus Richard O. , Zhang Fajian 
Published: April 2011

ABSTRACTGiant magnetoresistance (GMR) as large as 25% at 25°C has been observed for multilayer ultrathin films of iron oxide (Fe3O4) nanoclusters and polyimide molecules alternately adsorbed onto single crystal silicon and quartz substrates using a novel self-assembly technique. This process involves the alternate dipping of a substrate into an aqueous solution of anionic polyimide precursor (polyamic salt, PAA) followed by dipping it into an aqueous solution of cationic polydiallyldimethylammonium chloride (PDDA)-coated Fe3O4, nanoparticles. The regular formation of alternating monolayers is verified by UV-vis spectroscopy and contact angle measurements. Vibrating sample magnetometry indicates the formation of ultrasoft films.
Air Force Application of Advanced Magnetic Materials
Authors: Fingers R.T. , Rubertus C. S. 
Published: April 2011

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.
Properties of Giant Magneto-Impedance Material for A Novel Integrating Magnetic Sensor
Authors: Gore J.G. , Tomka G.J. , Milne J. , Maylin M.G. , Squire P.T. , Atkinson D. 
Published: April 2011

ABSTRACTA novel magnetic field sensor, based on the giant magneto-impedance effect is described and analysed. The sensor utilises an amorphous wire, annealed under optimised conditions. The conditions required for the optimisation of the magnetic properties of the wire are shown. The wire can be up to 2m long, and integrates the field over the length of the wire. It operates in open-loop mode. With a bias field of ∼500 A/m it achieves a sensitivity of 0.02 A/m and linearity of better than 5% for external fields between ±300 A/m.
Magnetic Force Microscopy Study of New Nanocrystalline Soft Magnetic Ribbons.
Authors: Hawley M. E. , Brown G. W. , Thoma D. J. , Willard M. A. , Laughlin D. E. , McHenry M. E. 
Published: April 2011

ABSTRACTNew nanocrystalline, multicomponent extremely soft magnetic materials with superior high temperature magnetic properties hold great promise in power applications. Fabricated in ribbon form by rapid solidification methods, the initial material is amorphous. By controlled annealing procedures, the amorphous material was transformed into a nanocrystalline form with the degree of crystallinity determined by the annealing temperature and time. The magnetic structures of ribbons, as-fabricated and annealed at temperatures from 550 to 750 °C were examined by magnetic force microscopy to determine the impact of residual stress and nanocrystallinity on the observed structure. A correlation was seen between the magnetic structures and surface microstructure. The wheel side of the as-processed ribbon was rougher than the top side of the ribbon and a complicated magnetic domain structure was present in the amorphous material. After annealing, nanocrystals formed, increasing in size with increasing temperature. The lowest temperature annealed sample had a bimodal grain size distribution and a combination of stripe and localized domains. After annealing little difference was seen between the two sides of the ribbons. Stripe domains were absent in the ribbons annealed at the highest temperatures.
Processing Sm-Fe(Ta)-N hard magnetic materials
Authors: Žužek K , Mcguiness PJ , Kobe S 
Published: April 2011

ABSTRACTSmFe based alloys interstitially modified with nitrogen are potential candidates for high energy permanent magnets. In order to obtain the optimum properties a thorough understanding of the starting material and processing parameters is required. The microstructures of two cast alloys of composition Sm13.8Fe82.2 Ta4.0 and Sm13.7 Fe86.3 were carefully examined with a SEM equipped with EDX and the exact stoichiometries of the phases were determined. The SmFeTa material was found to contain significant amounts of TaFe2as well as the Sm2Fe17, SmFe2, SmFe3 phases observed in the SmFe material but without the a-iron dendrites which are characteristic of the latter material. The optimum conditions necessary to provide the highest coercivities using the conventional HDDR process, and for the HDDR process combined with pre-milling were investigated. The coercivities obtained after using the HDDR process and subsequent nitriding were 680 kA/m for the SmFeTaN and 360 kA/m for the SmFeN samples. Significantly higher coercivites of 1000 kA/m for SmFeN and 1275 kA/m for SmFeTaN were achieved by reducing the particle size with milling prior to the HDDR process.The better coercivities obtained with the Ta containing sample were found to be due to the presence of a much smaller amount of a. The milling prior to the HDDR treatment improves the magnetic properties because of the small particle size which prevents the grains growing too large, with their consequent very negative effect on the coercivity.
Neutron Diffraction Characterization of Permanent Magnet Phases
Authors: Yelon William B. 
Published: April 2011

ABSTRACTNeutron diffraction has been invaluable in the characterization of intermetallic magnetic phases due to the unique properties of the neutron and the availability of high performance powder diffractometers that allow large numbers of samples to be investigated. The structural data derived from these studies serves as fundamental input for theory, and constraints on analyses of data from other methods, such as Mossbauer spectroscopy. The empirical structure-property relations derived from these studies serves to guide synthesis of new compounds and may help to define the next generation of high performance permanent magnets.
Dislocation Structure and Deformation Behavior of Intermetallic Compounds
Authors: Mills M. J. , Viswanathan G. B. , Srinivasan R. , Savage M.F. , Noebe R.D. , Daw M. S. 
Published: April 2011

AbstractThe fine structure of dislocations in intermetallic compounds can have a profound influence on their macroscopic mechanical properties. The development of appropriate models of deformation requires consideration of dislocation core structure, possible dissociation or decomposition reactions, overall dislocation morphology and relevant dislocation interactions based on detailed transmission electron microscopy study. This empirical information may be rationalized based on both atomistic and continuum-level dislocation modeling. The specific cases of jogged 1/2<110] ordinary dislocations in γ-TiAl and a<101> superdislocations in NiAl are discussed.
Study of the Mechanical Behavior of BCC Transition Metals Using Bond-Order Potentials
Authors: Mrovec M. , Vitek V. , Nguyen-Manh D. , Pettifor D. G. , Wang L. G. , Sob M. 
Published: April 2011

AbstractDeformation properties of body-centered-cubic transition metals are controlled by the core structure of screw dislocations and their studies involve extensive computer simulations. In this paper we present the recently constructed bond-order potentials (BOP) that are based on the realspace parametrized tight-binding method. In order to examine the applicability of the potentials we have evaluated the energy differences of alternative structures, investigated several transformation paths leading to large distortions and calculated phonon dispersions. Using these potentials we have calculated γ-surfaces that relate to the dislocation core structures and discuss then the importance of directional bonding in studies of dislocations in transition metals.
Computer Simulation of the Effect of Copper on Defect Production and Damage Evolution in Ferritic Steels
Authors: Perlado J. M. , Marian J. , Lodi D. , De La Rubia T. Díaz 
Published: April 2011

AbstractIt has long been noticed that the effect of Cu solute atoms is important for the microstructural evolution of ferritic pressure vessel steels under neutron irradiation conditions. Despite the low concentration of Cu in steel, Cu precipitates form inside the α-Fe surrounding matrix and by impeding free dislocation motion considerably contribute to the hardening of the material. It has been suggested that Cu-rich clusters and combined Cu solute atoms-defect clusters that may act as initiating structures of further precipitates nucleate during annealing of displacement cascades. In order to assess the importance of the different mechanisms taking place during collision events in the formation and later evolution of these structures, a detailed Molecular Dynamics (MD) analysis of displacement cascades in a Fe-1.3% at. Cu binary alloy has been carried out. Cascade energies ranging from 1 to 20 keV have been simulated at temperatures of 100 and 600 K using the MDCASK code, in which the Ackland-Finnis-Sinclair many-body interatomic potential has been implemented. The behaviour of metastable Cu selfinterstitial atoms (SIAs) in the form of mixed Fe-Cu features is studied as well as their impact on the resulting defect structures. It is observed that above 300 K generated Cu SIAs undergo recombination with no substantial effect on the after-cascade microstructure while at 100 K Cu SIAs remain sessile and exhibit a considerable binding to interstitial and vacancy clusters. Finally, the effect that the production of vacancies via collision cascades may have on the self diffusion of Cu solute atoms is quantitatively addressed by means of determining diffusion coefficients for Cu atoms under different microstructural conditions.
Study of Electrical Properties of Dislocations in ZNS Using Electric Force Microscopy
Authors: Bai G. F. , Petrenko V. F. , Baker I. 
Published: April 2011

AbstractA combination of electric force microscopy (EFM) and non-contact scanning force microscopy (SFM) was used to study micro-indentation-induced dislocation bands in sphaleritic ZnS single crystals. Large local distortions in electrical potential from the dislocation bands were observed in the EFM images. For the first time, the electric charges of resting partial Zn(g) and S(g) dislocations were determined quantitatively. The results compare well with theoretical models.