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ABSTRACT: Structural, magnetic properties and magnetostriction studies of Sm1-xNdxFe1.55 (0 <= x <= 0.56) alloys have been performed. X-ray diffraction analysis confirms the presence of single cubic Laves phase in Sm1-xNdxFe1.55 alloys with 0 <= x <= 0.48. The lattice parameter of alloys increases linearly with increase in Nd content while the Curie temperature behaves in the opposite way. The alloy x=0.08 exhibits a giant magnetostriction value(lambda(parallel to)-lambda(perpendicular to)) of -2187 ppm at a magnetic field of 12 kOe due to the anisotropy compensation between Sm3+ and Nd3+ ions. (C) 2010 Elsevier B.V. All rights reserved.
Journal of Magnetism and Magnetic Materials. 01/2010; 322(15):2095-2098.
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ABSTRACT: Carbon doping effects in MnAs alloys have been investigated. More carbon doping in MnAs alloys leads to lower Curie temperature, larger thermal hysteresis and sharper slope of the dependence of critical field on reduced temperature due to severe lattice distortion. The obtained maximum of magnetic entropy change for a field change of 5 T is about 12.8 Jkg(-1) K-1 near room temperature, and increases with more doping carbon content to about 22.4 Jkg(-1) K-1 in MnAsC0.03 and 13.2 Jkg(-1) K-1 in MnAsC0.05. (C) 2010 Elsevier B.V. All rights reserved.
Journal of Magnetism and Magnetic Materials. 01/2010; 322(15):2223-2226.
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ABSTRACT: Rhombohedral LaMnO3+delta powders were successfully synthesized by annealing gel precursors obtained by a polymerized complex method. The average grain size increases with increasing calcination temperature. The zero-field-cooled (ZFC) and field-cooled (FC) magnetization curves indicate that LaMnO3+delta compounds obtained at 700 and 800 degrees C are ferromagnetic, while both ferromagnetic and antiferromagned c components are present in those calcined at 900 and 1000 degrees C. This is because the concentration of Mn4+ ions drops with increasing calcination temperature. The temperature dependence of the resistivity of LaMnO3+delta Compounds exhibits an insulator-metal transition at about 90 K and also a low-temperature upturn with a resistivity minimum at about 40 K. Upon increasing particle size, the zero-field resistivity of the LaMnO3+delta powders increases due to suppression of the conduction by the insulating antiferromagnetic component. The negative magnetoresistance of a sample pellet prepared at 700 degrees C ranges from - 82% to - 88% in the temperature range of 40-100 K due to suppression of the spin-dependent scattering by an applied field. (C) 2009 Elsevier B.V. All rights reserved.
Physica B-Condensed Matter. 01/2010; 405(5):1362-1368.
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ABSTRACT: Electromagnetic-wave absorption properties of FeNiMo/C nanocapsules with FeNiMo nanoparticles as cores and carbon as shells have been studied. The FeNiMo/C nanocapsules, synthesized by arc-discharging Fe11Ni79Mo10 (at.%) alloy in ethanol, exhibited outstanding reflection loss (RL < -20 dB) in the range of 13-17.8 GHz with an absorber thickness of 1.7 mm, and an optimal RL of -64.0 dB was obtained at 13.2 GHz with an absorber thickness of 1.9 mm. The broadest bandwidth (RL < -10 dB) from 9 to 18 GHz, covering the whole Ku-band (12.4-18 GHz) and almost the whole X-band (9-12.4 GHz), was achieved for a 2 mm layer. The excellent electromagnetic properties are ascribed to the good match between high permeability from the core of FeNiMo nanoparticles and low permittivity from the special core/shell microstructure in the FeNiMo/C nanocapsules. (C) 2010 Elsevier BM. All rights reserved.
Journal of Alloys and Compounds. 01/2010; 506(2):826-830.
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ABSTRACT: The HoCo2 nanoparticles are found to be stable in air without any shell protection. The HoCo2 nanoparticles display superparamagnetic properties between their blocking temperature of 40 K and Curie temperature of 78 K. The magnetic-entropy change increases with decreasing temperature at a certain magnetic-field change, which is ascribed to the competition between the Zeeman energy and thermal-agitation energy at low temperatures. A large magnetic-entropy change of 19.4 J kg(-1) K-1 was found at 7.5 K in an applied-field change from 1 to 7 T, while 6.1 J kg(-1) K-1 was achieved in a low field change of 1 T. HoCo2 nanoparticles are useful for application of magnetic refrigeration at low temperatures.
Journal of Nanoparticle Research. 01/2010; 12(4):1167-1172.
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ABSTRACT: It is shown that the superconductivity in Ce1-xGdxFeAsO0.84F0.16 compounds can be modulated by internal (chemical) pressure. The internal pressure is induced by Gd substitution for Ce in CeFeAsO0.84F0.16, which compresses the crystal lattice. The temperature dependences of resistivity and magnetization show that the superconducting-transition temperature T-c is enhanced from 40 K for CeFeAsO0.84F0.16 to 47.5 K for Ce0.6Gd0.4FeAsO0.84F0.16. The increase and subsequent decrease of Tc upon application of external pressure, as observed previously in LaFeAsO0.89F0.11, is entirely confirmed by the modulation of Tc of the Ce1-xGdxFeAsO0.84F0.16 superconductors by internal pressure.
Superconductor Science & Technology. 01/2010; 23(2).
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ABSTRACT: Magnetic properties and magnetocaloric effect of the ferrimagnetic compounds Gd <sub>4</sub> Co <sub>3</sub> and ( Gd <sub>0.9</sub> Dy <sub>0.1</sub>)<sub>4</sub> Co <sub>3</sub> have been studied. In Gd <sub>4</sub> Co <sub>3</sub> , two successive magnetic-entropy changes occur due to a spin-reorientation transition at T<sub> SR </sub>=163 K and a ferrimagnetic-magnetic ordering transition at T<sub>C</sub>=220 K . For a field change from 0 to 5 T, -ΔS<sub>M</sub><sup> max </sup> at T<sub>C</sub> is 5.74 J / kg K , the full width at half maximum (δT<sub> FWHM </sub>) of the -ΔS<sub>M</sub> versus T curve has a high value of 131 K, and the refrigerant capacity is as high as 575 J/kg. T<sub>C</sub> can easily be tuned by Dy substitution for Gd and the magnetic-entropy change is increased simultaneously. -ΔS<sub>M</sub><sup> max </sup> of ( Gd <sub>0.9</sub> Dy <sub>0.1</sub>)<sub>4</sub> Co <sub>3</sub> at T<sub>C</sub>=145 K for the same field change has increased to 8.47 J / kg K . Our studies suggest that the successive magnetic transitions could enlarge the temperature interval, which makes this type of material meaningful for magnetic refrigeration in wider temperature regions than conventional materials.
Journal of Applied Physics 04/2009; · 2.17 Impact Factor
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ABSTRACT: HoAl2/Al2O3 nanocapsules with a core of HoAl2 and a shell of amorphous Al2O3 have been synthesized. The formation of the rare-earth compound nanocapsules can be ascribed to the different melting points and the optimal proportions of Ho and Al atoms during the arc-discharging process. Furthermore, the formation of the Al2O3 shell protects the rare-earth atoms from serious oxidation. The HoAl2/Al2O3 nanocapsules display superparamagnetic properties between the blocking temperature of 6 K and the Curie temperature of 26 K. The absolute value of the magnetic-entropy change in the HoAl2/Al2O3 nanocapsules rapidly increases with the decrease in temperature and reaches 14.7 J kg(-1) K-1 at 3K for a magnetic-field change from 0 to 70 kOe. As a result, this new type of nanocapsule may be applied, in the temperature range studied, in cryogenic magnetic-refrigerator devices.
Journal of Physics D-Applied Physics. 01/2009; 42(4).
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ABSTRACT: The natural resonance appears at 16 GHz for (Fe, Ni)/C nanocapsules with (Fe, Ni) alloys as cores and graphite as shells. Reflection loss (RL) exceeding -10 dB was obtained in the whole Ku-band (12.4-18 GHz) for an absorber thickness of 2.0 mm, while it exceeds -20 dB over the 13.6-16.6 GHz range. In addition, the bandwidth does not change dramatically for the thicknesses of 1.87-2.1 mm for the RL values exceeding -10 dB. The (Fe, Ni)/C nanocapsules with wide bandwidth absorption can be used as excellent electromagnetic-wave-absorption materials in the whole Ku-band. (C) 2008 Elsevier Ltd. All rights reserved.
Carbon. 01/2009; 47(2):470-474.
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ABSTRACT: The C15 Laves phases with composition Nd1-xPrx(Fe0.35Co0.55B0.1)(2) (0 <= x <= 1) have been synthesized by arc melting and subsequent annealing. The Curie temperature T-c and the saturation magnetizations M-s at 5 and 295 K decrease with increasing Pr content. The linear anisotropic magnetostriction lambda(a) = lambda(parallel to)-lambda(perpendicular to) at room temperature for Nd1-xPrx(Fe0.35Co0.55B0.1)(2) alloys with 0 <= x <= 0.4 initially reaches a negative minimum, then increases and changes its sign with increasing magnetic field H, and the lambda(a) for the alloys with x >= 0.6 is positive and increases as magnetic field H increases. (C) 2008 Elsevier B.V. All rights reserved.
Journal of Magnetism and Magnetic Materials. 01/2008; 320(19):2373-2375.
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ABSTRACT: Fluorescence (FL) and microwave-absorption properties of multi-functional alpha-Fe solid-solution nanocapsules have been investigated. High-resolution transmission electron microscopy and x-ray photoelectron spectroscopy analysis show that the nanocapsules have a shell/core structure with alpha-Fe solid-solution nanoparticles as the core and amorphous ZnO as the shell. The nanocapsules are ferromagnetic at room temperature. There is a tendency to redshift for the peak at 388 nm in the FL spectra as the Zn concentration decreases. The in-depth study of relative permittivity and permeability reveals that the ZnO-coated alpha-Fe solid-solution nanocapsules exhibit excellent microwave-absorption properties, because of a proper electromagnetic match in the microstructure, strong natural resonances and dipolar polarization mechanisms.
Journal of Physics D-Applied Physics. 01/2008; 41(17).
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ABSTRACT: TbAl2 nanocapsules with a core of TbAl2 compound and a shell of amorphous Al2O3 were synthesized by the arc-discharge technique using modified strategies. The TbAl2 nanocapsules display superparamagnetic properties between the blocking temperature of 70 K and the Curie temperature of 100 K. The absolute value of the change of magnetic entropy of the TbAl2 nanocapsules rapidly increases with decreasing temperature, reaching 23.83 J kg(-1) K-1 at 7.5 K with a magnetic field change of 70 kOe. Crown Copyright (c) 2008 Published by Elsevier Ltd. on behalf of Acta Materialia Inc. All rights reserved.
Scripta Materialia. 01/2008; 59(3):340-343.
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ABSTRACT: Al2O3-coated FeCo nanocapsules were synthesized by the arc-discharge method and three-dimensional wire-like macro-aggregates were self-assembled simultaneously by nanocapsules. The electromagnetic (EM) parameters (i.e. the relative permeability and permittivity) were measured at 2-18 GHz. As a consequence of the surface-and shape-anisotropy energy of the nanocapsules, a natural resonance at 6 GHz is dominant in the microwave absorption properties. A reflection loss (RL) exceeding - 20 dB was obtained in the frequency range 4.2-18 GHz for absorber thicknesses of 1.3-6 mm. An optimal RL of - 51 dB was found at 10.2 GHz for an absorber thickness of 2 mm. As a result, the Al2O3-coated FeCo nanocapsules show good prospects of being applied in EM wave absorptive devices.
Journal of Physics D-Applied Physics. 01/2008; 41(17).
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ABSTRACT: The natural resonance appears at 16 GHz for (Fe, Ni)/C nanocapsules with (Fe, Ni) alloys as cores and graphite as shells. Reflection loss (RL) exceeding −10 dB was obtained in the whole Ku-band (12.4–18 GHz) for an absorber thickness of 2.0 mm, while it exceeds −20 dB over the 13.6–16.6 GHz range. In addition, the bandwidth does not change dramatically for the thicknesses of 1.87–2.1 mm for the RL values exceeding −10 dB. The (Fe, Ni)/C nanocapsules with wide bandwidth absorption can be used as excellent electromagnetic-wave-absorption materials in the whole Ku-band.
Carbon.
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ABSTRACT: TbAl2 nanocapsules with a core of TbAl2 compound and a shell of amorphous Al2O3 were synthesized by the arc-discharge technique using modified strategies. The TbAl2 nanocapsules display superparamagnetic properties between the blocking temperature of 70 K and the Curie temperature of 100 K. The absolute value of the change of magnetic entropy of the TbAl2 nanocapsules rapidly increases with decreasing temperature, reaching 23.83 J kg−1 K−1 at 7.5 K with a magnetic field change of 70 kOe.
Scripta Materialia. 59(3):340-343.
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ABSTRACT: The C15 Laves phases with composition Nd1−xPrx(Fe0.35Co0.55B0.1)2 (0⩽x⩽1) have been synthesized by arc melting and subsequent annealing. The Curie temperature Tc and the saturation magnetizations Ms at 5 and 295 K decrease with increasing Pr content. The linear anisotropic magnetostriction λa=λ∥−λ⊥ at room temperature for Nd1−xPrx(Fe0.35Co0.55B0.1)2 alloys with 0⩽x⩽0.4 initially reaches a negative minimum, then increases and changes its sign with increasing magnetic field H, and the λa for the alloys with x⩾0.6 is positive and increases as magnetic field H increases.
Journal of Magnetism and Magnetic Materials.
