C. B. Rong

University of Texas at Arlington, Arlington, Texas, United States

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Publications (17)54.96 Total impact

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    ABSTRACT: Nd2Fe14B/α-Fe-based hard/soft nanocomposite magnets with Co addition have been prepared by ball-milling and warm compaction. It was found that Co addition into the magnetically hard phase improves magnetic properties significantly, especially the remanence ratio and coercivity. The effect on the magnetic properties of the selective Co addition may be attributed to enhanced interdiffusion across the hard/soft interface that improves the interface conditions for effective interphase exchange coupling. By optimizing the Co content in the Nd15Fe79−xCoxB6 hard phase, an energy product value about 21 MG Oe can be obtained in the isotropic Nd2(FeCo)14B/α-(FeCo) nanocomposite magnets compared with 15 MG Oe of Nd2Fe14B/α-Fe nanocomposite magnets prepared under the same conditions with the same grain size and microstructure, owing to the strengthened intergranular exchange interactions.
    No preview · Article · Dec 2012 · Journal of Physics D Applied Physics
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    X. Y. Xiong · C. B. Rong · S. Rubanov · Y. Zhang · J. P. Liu
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    ABSTRACT: The microstructure and compositions of the bulk nanocomposite SmCo/Fe permanent magnet were studied using transmission electron microscopy and 3-dimensional atom probe techniques. The excellent magnetic properties were related to the uniform nanocomposite structure with nanometer α-Fe particles uniformly distributed in the SmCo phase matrix. The α-Fe phase contained ∼26at% Co, and the SmCo phase contained ∼19at% Fe, confirming that the interdiffusion of Fe and Co atoms between the two phases occurred. The formation of the α-Fe(Co) phase explained why the saturation magnetization of the nanocomposite permanent magnet was higher than that expected from the original pure α-Fe and SmCo5 powders, which enhanced further the maximum energy product of the nanocomposite permanent magnet.
    Full-text · Article · Nov 2011 · Journal of Magnetism and Magnetic Materials
  • M. Yue · Y. P. Wang · N. Poudyal · C. B. Rong · J. P. Liu
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    ABSTRACT: Nd–Fe–B nanoparticles have been obtained by using surfactant-assisted ball milling and subsequent size-selection technique. Structural analyses show that nanoparticles with two particle sizes around 10 and 100 nm were obtained. The partially amorphous Nd–Fe–B nanoparticles give their room-temperature coercivities around 0.1 and 1.5 kOe for the small and large nanoparticles, respectively. As the temperature decreases to 200 K, the coercive force of the large nanoparticles increases by 50% due to the enhancement of the magnetocrystalline anisotropy of the Nd2Fe14B phase in the particles.
    No preview · Article · Feb 2009 · Journal of Applied Physics
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    J. D. Zou · B. G. Shen · J. R. Sun · J. Shen · C. B. Rong · W. Li
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    ABSTRACT: The essence of the anomalous Hall effect (AHE) is not fully understood and it still attracts considerable attention. Magnetic and magnetotransport properties of Ce Fe <sub>1.95</sub> Al <sub>0.05</sub> compound in diverse magnetic state are studied which is helpful to know the essence of AHE. The semiempirical relation ρ<sub>xy</sub>=R<sub>0</sub>B+4πR<sub>s</sub>M , widely accepted, is valid in describing the behaviors of AHE in ferromagnetic and paramagnetic state, but invalid in antiferromagnetic state in Ce Fe <sub>1.95</sub> Al <sub>0.05</sub> compound.
    Full-text · Article · May 2008 · Journal of Applied Physics
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    ABSTRACT: The magnetization reversal in very small FePt particles is investigated by analytical and numerical calculations. The modeling focuses on particles with diameters from 3 to 15 nm , as produced by a salt-matrix annealing technique. Experiment shows that the particles exhibit a certain degree of structural inhomogenity, which has a far-reaching effect on the magnetic hysteresis. In particles larger than about 10 nm , the magnetization-reversal mode is strongly inhomogeneous, and there are several scenarios that depend on the symmetry of inhomogenity. Small particles reverse nearly coherently, and the coercivity is essentially equal to the volume-averaged anisotropy. In this case, nonrectangular hysteresis loops reflect factors such as grain misalignment, particle-size distribution, and different degrees of L1<sub>0</sub> order in different particles.
    Preview · Article · May 2008 · Journal of Applied Physics
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    ABSTRACT: A comparable study of the microstructure and magnetic properties was performed for magnetite films deposited on (100)-oriented MgO and Sr Ti O <sub>3</sub> (STO) substrates. The growth of strained high quality Fe <sub>3</sub> O <sub>4</sub> films was confirmed by x-ray diffraction analysis and Raman spectroscopy measurements. The surface morphology and magnetic properties of the two films were found to be obviously different. Moreover, a stripelike magnetic domain structure was observed in the film on STO. Substrate-induced strain is believed to be responsible for these observations, which significantly affects the magnetic anisotropy and the magnetic coupling at the antiphase boundaries in the films.
    Full-text · Article · May 2008 · Journal of Applied Physics
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    ABSTRACT: Phase transition processes and magnetocaloric effect in Ni2.15Mn0.85-xCoxGa (x=0.03, 0.04, 0.05, and 0.06) alloys were investigated. The alloys exhibit nonmodulated tetragonal martensitic structure at room temperature. According to experiment results, Ni2.15Mn0.85-xCoxGa alloys undergo a magnetostructural phase transition on the heating process when electron concentration is in the range from 7.633 to 7.643. The alloys also show large magnetic entropy changes. With increasing Co content, the magnetic entropy change decreases.
    Full-text · Article · Apr 2008 · Journal of Applied Physics
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    F. X. Hu · J. R. Sun · B. G. Shen · C. B. Rong · J. Gao
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    ABSTRACT: We report the switching behavior of resistive states induced by current flowing in La1−xCaxMnO3 films. The transport behavior upon treatments by applying a large dc current has been investigated in the absence of magnetic field. A switching from low to high resistive state was found upon applying a large dc current for the both compositions. The critical currents for the switching are 10.5 mA (density of 2.3×103 A/cm2) and 6.7 mA (density of 1.6×103 A/cm2) for compositions x = 0.2 and 0.3, respectively. Our repeated measurements indicate that the high resistive state appeared in the film x = 0.2 is much stable. Exposing the sample in air and room temperature does not cause any change of the transport properties. However, for the film with x = 0.3, the induced high resistive state behaves with unstable characteristics. Keeping the sample at a low temperature of 20 K, a relaxation to a higher resistive state takes place. The mechanism of phase separation was taken into account in the interpretation of the observed phenomena.
    Preview · Article · Jan 2008 · Journal of Applied Physics
  • F. X. Hu · J. R. Sun · B. G. Shen · C. B. Rong · J. Gao
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    ABSTRACT: We report the growth of colossal magnetoresistive (CMR) films La0.7Ca0.3MnO3 (LCMO) and La0.9Ba0.1MnO3 (LBMO) onto Si (100) using a simple pulsed-laser deposition technique. To avoid oxidation of the Si surface, an initial growth of SrTiO3 of a few atomic layers was carried out. We found that epitaxial growth of LCMO and LBMO films on Si can be realized by optimizing the deposition process. The obtained LCMO and LBMO films show ferromagnetic nature and the resulted LCMO/Si and LBMO/Si heterojunctions exhibit good rectifying behavior with magnetically tunable characteristics.
    No preview · Article · Jan 2008 · Journal of Applied Physics
  • Y. L. Hou · Z. C. Xu · S. Peng · C. B. Rong · J. P. Liu · S. H. Sun
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    ABSTRACT: A facile synthesis of SmCo5 magnets was investigated using the high-temperature reductive annealing of core/shell-structured Co/Sm 2O3 nanoparticles. The magnets have the ability to adopt a hcp structure with a coercivity value of 24 kOe at 100 K and 8 kOe at room temperature. The core/shell particles are reductively annealed in the presence of Ca at 900°C to reduce Sm2O3 to Sm and enhance interface diffusion between Co and Sm. Energy dispersive spectroscopy (EDS) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) were employed to determine the composition of the particles. X-ray diffraction (XRD) was also used to characterize the structure of the particles. Results show that synthesis can be effective for fabricating air-stable SmCo-based nanoparticles and nanocomposite magnets.
    No preview · Article · Sep 2007 · Advanced Materials
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    ABSTRACT: The size dependence of the chemical-ordering parameter and magnetic-ordering properties coercivity, magnetization and curie temperature of fct-FePt nanoparticles was investigated. Transmission electron microscopy (TEM) was used for the FePt nanoparticles with different sizes before and after annealing in a salt matrix. TEM observation revealed that when the particle size is smaller than or equal to 8 nm the fct nanoparticles are monocrystaline whereas the 15 nm fct nanoparticles are polycrystalline. The magnetic ordering temperatures of ferromagnets with reduced size in all three dimensions have been little studied and this was addressed by applying the salt-matrix-annealing technique. To understand strong size dependence of the Curie temperature the finite-size scaling theory was used to fit the behavior. It was observed that long range ordering parameter decreases with decreasing particle size.
    Full-text · Article · Nov 2006 · Advanced Materials
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    ABSTRACT: Nanocomposite Pr9Fe74 Co12B5 and Pr9Fe74 Co12B5Sn0.5 ribbons were directly prepared by melt-spinning. Measurements of reversible and irreversible magnetization and magnetic viscosity were performed on the ribbons. It is found that the demagnetization curves of the both samples show a single hard phase behavior at room temperature, while a two-phase behavior at low temperature. The sample with Sn addition, because of its more homogeneous microstructure, shows a more obvious two-phase behavior than the Sn free one at low temperature. Furthermore, the increase of the volume fraction and grain sizes of the soft phase, in the Sn-doped ribbons, increases the portions of reversible magnetization and decreases the nucleation field Hn. The investigation of the magnetic viscosity shows that the activation volume is related to the grain sizes of the soft phase.
    No preview · Article · Dec 2005
  • S.-L. He · H.-W. Zhang · C.-B. Rong · R.-J. Chen · J.-R. Sun · B.-G. Shen
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    ABSTRACT: The single-phase nanocrystalline Pr2Fe14B magnets composed of cubic-shaped and irregular-shaped grains is built. The magnetic hysteresis loops are simulated by micromagnetism finite element method. The remanence, coercivity and maximum energy product decrease with deteriorated grain alignment. Attributed to strong intergrain exchange coupling (IGEC), the variation of magnetic properties with alignment degree is significantly affected by the average grain size in nanocrystalline magnets. The investigation shows the increase of coercivity with improved grain alignment in nanocrystalline magnets, which is completely different from the phenomena in sintered magnets.
    No preview · Article · Jul 2005
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    ABSTRACT: The initial curves, demagnetization curves and recoil curves of Pr2Fe14B and Pr2Fe14 B/α-Fe nanocrystalline permanent magnets have been calculated by micromagnetic finite-element method. The validity of δm(H) curves, which can be used to determine the strength of intergrain exchange coupling interaction (IGEC), is approved by the calculated results. It is found that IGEC weakens with increasing grain size D for single-phase nanocrystalline and nanocomposite permanent magnets. Thus, the demagnetization curve shows a two-phase behavior and the Sm(H) curve shows two peaks for the nanocomposite sample with D = 20 nm. The peak at small field can be attributed to the exchange interaction between the magnetic hard and soft grains, while the peak at large field may be due to the IGEC among hard grains.
    No preview · Article · Dec 2004
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    ABSTRACT: The influence of microstructure on magnetic properties of Sm(Co, Cu, Fe, Zr)z magnets is investigated by micromagnetic finite-element method. The demagnetization curves at different temperatures are also simulated. The calculated results show that the saturation polarization Js depends on the relative proportions of 2:17 phase and 1:5 phase. The coercivity and the maximum energy product increase with increasing 2:17-type cell size, while they decrease with increasing width of 1:5-type cell boundary. The coercivity analysis shows that the magnetization reversal in Sm(Co, Cu, Fe, Zr)z magnets is mainly controlled by nucleation at cell boundary. The abnormal temperature dependence of coercivity is due to the fact that the cell boundary becomes less magnetic even nonmagnetic and the nucleation is difficult with increasing temperature.
    No preview · Article · Dec 2004
  • H.-W. Zhang · C.-B. Rong · S.-Y. Zhang · B.-G. Shen
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    ABSTRACT: The microstructure with which a hard magnetic phase precipitates from the soft magnetic matrix, is observed in nanocomposite Pr2Fe14B/α-Fe. The magnetic hysteresis loops are simulated by micromagnetic finite element method. The dependence of remanence, coercivity and maximum energy product on the width of soft phase are discussed in detail. Although a single-hard-magnetic-phase behavior is observed, the coercivity decreases monotonically with the increase of soft phase width from 0 to 12 nm. The obtained maximum energy products are 184 and 674 kJ/m3 for isotropic and anisotropic magnets, respectively.
    No preview · Article · Dec 2004
  • H.-W. Zhang · C.-B. Rong · J. Zhang · S.-Y. Zhang · B.-G. Shen
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    ABSTRACT: The magnetization reversal has been examined by the temperature dependence of the coercivity, the initial magnetization curve, minor hysteresis loops, and thermal activation in isotropic nanocrystalline Pr-Fe-B ribbons. The coercivity mechanism is found to vary with temperature. At 20 K, the coercivity is mainly determined by strong pinning (by random inhomogeneities); while at room temperature it is mainly controlled by the nucleation of domain and localized pinning at grain boundaries. The influence of the grain-boundary character on magnetic hardening and the temperature dependence of intergrain exchange coupling and anisotropy have been investigated to discuss the coercivity mechanism.
    No preview · Article · Nov 2002