The Experts below are selected from a list of 82512 Experts worldwide ranked by ideXlab platform
John Z Zhang - One of the best experts on this subject based on the ideXlab platform.
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controlled synthesis and magnetic properties of bimagnetic spinel ferrite cofe2o4 and mnfe2o4 nanocrystals with core shell architecture
Journal of the American Chemical Society, 2012Co-Authors: Qing Song, John Z ZhangAbstract:A combination of hard Phase CoFe2O4 and Soft Phase MnFe2O4 as the bimagnetic nanocrystals in a core–shell architecture has been synthesized, and their magnetic properties have been systematically studied. Both HRTEM and EDS results confirmed the formation of bimagnetic core–shell structured nanocrystals. On the basis of the systematic and comparative studies of the magnetic properties of a mechanical mixture of pure CoFe2O4 and MnFe2O4 nanocrystals, chemically mixed Co1–xMnxFe2O4 nanocrystals, and bimagnetic core–shell CoFe2O4@MnFe2O4 and MnFe2O4@CoFe2O4 nanocrystals, the bimagnetic core–shell nanocrystals show very unique magnetic properties, such as the blocking temperature and coercivity. Our results show that the coercivity correlates with the volume fraction of the Soft Phase as the theoretical hard–Soft Phase model has suggested. Furthermore, switching the hard Phase CoFe2O4 from the core to the shell shows great changes in the coercivity of the nanocrystals. The bimagnetic core–shell nanocrystals e...
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controlled synthesis and magnetic properties of bimagnetic spinel ferrite cofe2o4 and mnfe2o4 nanocrystals with core shell architecture
Journal of the American Chemical Society, 2012Co-Authors: Qing Song, John Z ZhangAbstract:A combination of hard Phase CoFe(2)O(4) and Soft Phase MnFe(2)O(4) as the bimagnetic nanocrystals in a core-shell architecture has been synthesized, and their magnetic properties have been systematically studied. Both HRTEM and EDS results confirmed the formation of bimagnetic core-shell structured nanocrystals. On the basis of the systematic and comparative studies of the magnetic properties of a mechanical mixture of pure CoFe(2)O(4) and MnFe(2)O(4) nanocrystals, chemically mixed Co(1-x)Mn(x)Fe(2)O(4) nanocrystals, and bimagnetic core-shell CoFe(2)O(4)@MnFe(2)O(4) and MnFe(2)O(4)@CoFe(2)O(4) nanocrystals, the bimagnetic core-shell nanocrystals show very unique magnetic properties, such as the blocking temperature and coercivity. Our results show that the coercivity correlates with the volume fraction of the Soft Phase as the theoretical hard-Soft Phase model has suggested. Furthermore, switching the hard Phase CoFe(2)O(4) from the core to the shell shows great changes in the coercivity of the nanocrystals. The bimagnetic core-shell nanocrystals evidently demonstrate the rational design capability to separately control the blocking temperature and the coercivity in magnetic nanocrystals by varying the materials, their combination, and the volume ratio between the core and the shell and by switching hard or Soft Phase materials between the core and shell. Such controls via a bimagnetic core-shell architecture are highly desirable for magnetic nanocrystals in various applications.
J E Garay - One of the best experts on this subject based on the ideXlab platform.
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synthesis of strontium ferrite iron oxide exchange coupled nano powders with improved energy product for rare earth free permanent magnet applications
arXiv: Materials Science, 2016Co-Authors: A D Volodchenkov, Yasuhiro Kodera, J E GarayAbstract:We present a simple, scalable synthesis route for producing exchange coupled Soft/hard magnetic composite powder that outperforms pure Soft and hard Phase constituents. Importantly, the composites is iron oxide based (SrFe12O19 and Fe3O4) and contain no rare earth or precious metal. The two step synthesis process consists of first precipitating, an Iron oxide/hydroxide precursor directly on top of SrFe12O19 nano-flakes, ensuring a very fine degree of mixing between the hard and the Soft magnetic Phases. We then use a second step that serves to reduce the precursor to create the proper Soft magnetic Phase and create the intimate interface necessary for exchange coupling. We establish a clear processing window; at temperatures below this window the desired Soft Phase is not produced, while higher temperatures result in deleterious reaction at the Soft/hard Phase interfaces, causing an improper ratio of Soft to hard Phases. Improvements of Mr, Ms, and (BH)max are 42%, 29% and 37% respectively in the SrFe12O19/Fe3O4 composite compared to pure hard Phase (SrFe12O19). We provide evidence of coupling (exchange spring behavior) with hysteresis curves, first order reversal curve (FORC) analysis and recoil measurements.
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synthesis of strontium ferrite iron oxide exchange coupled nano powders with improved energy product for rare earth free permanent magnet applications
Journal of Materials Chemistry C, 2016Co-Authors: A D Volodchenkov, Yasuhiro Kodera, J E GarayAbstract:We present a simple, scalable synthesis route for producing exchange coupled Soft/hard magnetic composite powder that outperforms pure Soft and hard Phase constituents. Importantly, the composites are iron oxide based (SrFe12O19 and Fe3O4) and contain no rare earth or precious metals. The two step synthesis process consists of first precipitating an iron oxide/hydroxide precursor directly on top of SrFe12O19 nano-flakes, ensuring a very fine degree of mixing between the hard and the Soft magnetic Phases. The second step involves the reduction of the precursor to create the appropriate Soft magnetic Phase and create the intimate interface necessary for exchange coupling. We establish a clear processing window; at temperatures below this window the desired Soft Phase is not produced, while the use of higher temperatures results in deleterious reaction at the Soft/hard Phase interfaces, causing an improper ratio of Soft to hard Phases. Improvements in Mr, Ms, and (BH)max are 42%, 29% and 37%, respectively, in the SrFe12O19/Fe3O4 composite compared to the pure hard Phase (SrFe12O19). We provide evidence of coupling (exchange spring behavior) with hysteresis curves, first order reversal curve (FORC) analysis and recoil measurements.
Qing Song - One of the best experts on this subject based on the ideXlab platform.
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controlled synthesis and magnetic properties of bimagnetic spinel ferrite cofe2o4 and mnfe2o4 nanocrystals with core shell architecture
Journal of the American Chemical Society, 2012Co-Authors: Qing Song, John Z ZhangAbstract:A combination of hard Phase CoFe2O4 and Soft Phase MnFe2O4 as the bimagnetic nanocrystals in a core–shell architecture has been synthesized, and their magnetic properties have been systematically studied. Both HRTEM and EDS results confirmed the formation of bimagnetic core–shell structured nanocrystals. On the basis of the systematic and comparative studies of the magnetic properties of a mechanical mixture of pure CoFe2O4 and MnFe2O4 nanocrystals, chemically mixed Co1–xMnxFe2O4 nanocrystals, and bimagnetic core–shell CoFe2O4@MnFe2O4 and MnFe2O4@CoFe2O4 nanocrystals, the bimagnetic core–shell nanocrystals show very unique magnetic properties, such as the blocking temperature and coercivity. Our results show that the coercivity correlates with the volume fraction of the Soft Phase as the theoretical hard–Soft Phase model has suggested. Furthermore, switching the hard Phase CoFe2O4 from the core to the shell shows great changes in the coercivity of the nanocrystals. The bimagnetic core–shell nanocrystals e...
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controlled synthesis and magnetic properties of bimagnetic spinel ferrite cofe2o4 and mnfe2o4 nanocrystals with core shell architecture
Journal of the American Chemical Society, 2012Co-Authors: Qing Song, John Z ZhangAbstract:A combination of hard Phase CoFe(2)O(4) and Soft Phase MnFe(2)O(4) as the bimagnetic nanocrystals in a core-shell architecture has been synthesized, and their magnetic properties have been systematically studied. Both HRTEM and EDS results confirmed the formation of bimagnetic core-shell structured nanocrystals. On the basis of the systematic and comparative studies of the magnetic properties of a mechanical mixture of pure CoFe(2)O(4) and MnFe(2)O(4) nanocrystals, chemically mixed Co(1-x)Mn(x)Fe(2)O(4) nanocrystals, and bimagnetic core-shell CoFe(2)O(4)@MnFe(2)O(4) and MnFe(2)O(4)@CoFe(2)O(4) nanocrystals, the bimagnetic core-shell nanocrystals show very unique magnetic properties, such as the blocking temperature and coercivity. Our results show that the coercivity correlates with the volume fraction of the Soft Phase as the theoretical hard-Soft Phase model has suggested. Furthermore, switching the hard Phase CoFe(2)O(4) from the core to the shell shows great changes in the coercivity of the nanocrystals. The bimagnetic core-shell nanocrystals evidently demonstrate the rational design capability to separately control the blocking temperature and the coercivity in magnetic nanocrystals by varying the materials, their combination, and the volume ratio between the core and the shell and by switching hard or Soft Phase materials between the core and shell. Such controls via a bimagnetic core-shell architecture are highly desirable for magnetic nanocrystals in various applications.
Bela Pukanszky - One of the best experts on this subject based on the ideXlab platform.
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thermal analysis of the structure of segmented polyurethane elastomers
Journal of Thermal Analysis and Calorimetry, 2009Co-Authors: Kristof Bagdi, Kinga Molnar, Bela PukanszkyAbstract:Polyurethanes were prepared from 4,4′-methylenebis (phenyl isocyanate) (MDI), 1,4-butanediol (BD), and poly(tetrahydrofurane) polyether polyol (PTHF) by melt polymerization. The –OH functional group ratio of polyol/total diol was kept constant at 0.4, while the ratio of the isocyanate and hydroxyl groups (NCO/OH) changed between 0.940 and 1.150. The thermal analysis of the polymers by DSC and DMTA measurements indicated several transitions. The three glass transition temperatures observed were assigned to the relaxation of the aliphatic –CH2– groups of the polyol, and to that of the Soft and hard segments, respectively. The glass transition temperature of the Soft and hard Phase changed with the NCO/OH ratio indicating changes in Phase structure and composition confirmed also by the maximum in the number of relaxing Soft segments. Changes in the relatively small number of end-groups result in considerable modification of mechanical properties. Strength is determined by molecular mass and interactions, while stiffness depends mainly on Phase structure. Surprisingly enough, –OH excess yields stiffer polymers, since the interaction of the –OH groups results in a decrease in the amount of the Soft Phase. A unique correlation was found between tensile modulus and the number of relaxing Soft segments.
Katerina Soulantica - One of the best experts on this subject based on the ideXlab platform.
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on the advantages of spring magnets compared to pure fept strategy for rare earth free permanent magnets following a bottom up approach
Journal of Magnetism and Magnetic Materials, 2017Co-Authors: Marc Pousthomis, Cyril Garnero, Cecile Marcelot, Thomas Blon, Simon Cayez, Caroline Cassignol, M Krispin, Raul Arenal, Katerina SoulanticaAbstract:Nanostructured magnets benefiting from efficient exchange-coupling between hard and Soft grains represent an appealing approach for integrated miniaturized magnetic power sources. Using a bottom-up approach, nanostructured materials were prepared from binary assemblies of bcc FeCo and fcc FePt nanoparticles and compared with pure L10-FePt materials. The use of a bifunctional mercapto benzoic acid yields homogeneous assemblies of the two types of particles while reducing the organic matter amount. The 650 °C thermal annealing, mandatory to allow the L10-FePt Phase transition, led to an important interdiffusion and thus decreased drastically the amount of Soft Phase present in the final composites. The analysis of recoil curves however evidenced the presence of an efficient interPhase exchange coupling, which allows obtaining better magnetic performances than pure L10 FePt materials, energy product above 100 kJ m−3 being estimated for a Pt content of only 33%. These results clearly evidenced the interest of chemically grown nanoparticles for the preparation of performant spring-magnets, opening promising perspective for integrated subcentimetric magnets with optimized properties.