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Your search keyword '"Chen, Weimeng"' showing total 29 results
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29 results on '"Chen, Weimeng"'

3. Field-dependent low-field enhancement in effective paramagnetic moment with nano-scaled Co3O4

Author

Chen, Weimeng, Chen, Chinping, and Guo, Lin

Subjects
Condensed Matter - Materials Science
Abstract

Paramagnetic (PM) properties of columnar cobaltosic oxide (Co3O4) nanoparticles, about 75 nm in diameter, have been investigated by magnetization measurements at T > TN = 39 K. In zero or low applied field, the effective PM moment per formula unit (FU), Mu_eff, enhances significantly from the bulk value of 4.14 Mu_B/FU. It decreases asymptotically from 5.96 Mu_B/FU at Happ = 50 Oe down to 4.21 Mu_B/FU as the applied field increases to Happ = 10 kOe. The field dependent PM properties are explained by a structural inversion, from the normal spinel (spin-only moment ~ 3.9 Mu_B/FU) to the inverse spinel structure (spin-only moment ~ 8.8 Mu_B/FU). The structural inversion is reversible with the variation of the applied field. The lattice structure becomes almost 100% normal spinel in the high field exceeding 10 kOe, as revealed by the magnitude of the effective PM moment. The reversible, field dependent structure inversion is an important property with promising application potential. It is interesting for the future investigations., Comment: 20 pages 4 Figures, J. Appl. Phys. In Press

Published
2010
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4. Surface magnetic states of Ni nanochains modified by using different organic surfactants

Author

Chen, Weimeng, Zhou, Wei, He, Lin, Chen, Chinping, and Guo, Lin

Subjects
Condensed Matter - Materials Science, Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

Three powder samples of Ni nanochains formed of polycrystalline Ni nanoparticles with an estimated diameter of about 30 nm have been synthesized by a wet chemical method using different organic surfactants. These samples, having magnetically/structurally core-shell structures, all with a ferromagnetic Ni core, are Ni@Ni3C nanochains, Ni@NiSG nanochains with a spin glass (SG) surface layer, and Ni@NiNM nanochains with a nonmagnetic (NM) surface layer. The average thickness of the shell for these three samples is determined as about 2 nm. Magnetic properties tailored by the different surface magnetism are studied. In particular, suppression in saturation magnetization usually observed with magnetic nanoparticles is revealed to arise from the surface magnetic states with the present samples., Comment: 23 pages, 6 figures included

Published
2010
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6. Well-aligned Nickel Nanochains Synthesized by a Template-free Route

Author

Chen Weimeng, Chen Chinping, Gao Xingyu, Wee ATS, Li Pengwei, and Wang Rongming

Subjects
Ni nanostructure, Magnetic anisotropy, X-ray absorption spectroscopy, Electron microscopy, Materials of engineering and construction. Mechanics of materials, TA401-492
Abstract

Abstract Highly uniform and well-aligned one-dimensional Ni nanochains with controllable diameters, including 33, 78, and 120 nm, have been synthesized by applying an external magnetic field without any surface modifying agent. The formation can be explained by the interactions of magnetic dipoles in the presence of applied magnetic field. Magnetic measurements demonstrate that the shape anisotropy dominates the magnetic anisotropy. The demagnetization factor, ∆N, is in the range of 0.23–0.36.

Published
2009
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10. Wet chemical synthesis and magnetic properties of core-shell nanocolumns of Ni(OH)(2)@Co(OH)(2) and their oxides

Author

Yao, Meng, Chen, Weimeng, Fan, Xia, Liu, Chenmin, Meng, Xiangmin, Guo, Lin, Chen, Chinping, Yao, Meng, Chen, Weimeng, Fan, Xia, Liu, Chenmin, Meng, Xiangmin, Guo, Lin, and Chen, Chinping

Abstract

Ni(OH)(2)@Co(OH)(2) core-shell nanocolumns have been synthesized by an easy wet chemical process. Characterizations reveal that the layer structure is formed by stacking of several hexagonal nanosheets along the [001] direction. Each sheet is found to be of good crystallinity according to high-resolution transmission electron microscopy, with Ni(OH)(2) in the central and Co(OH)(2) in the peripheral region. The diagonal length of the hexagon is about 700-900 nm and the height of the nanocolumn is about 140-200 nm, with each nanosheet of about 20 nm in thickness. Upon calcination, the Ni(OH)(2)@Co(OH)(2) nanocolumns become a porous NiO@Co(3)O(4) nanostructure. At low temperature, Ni(OH)(2)@Co(OH)(2) exhibits an antiferromagnetic (AFM) transition at T(N) = 12 K. This is from Co(OH)(2) while the AFM transition of Ni(OH)(2), expected at 25 K, is not observed. A freezing temperature is also observed at T(F) = 7.5 K most likely arising from the randomly oriented moments in the outermost surface of Co(OH)(2). After the calcination, the AFM transition of Co(3)O(4) in the porous NiO@Co(3)O(4) nanostructure is observed at 28 K, which is much reduced from the bulk value of T(N) = 40 K, probably arising from the finite size effect. The characteristic dimension with the porosity is thus determined as about 8 nm.

Published
2011

27. Uniform α-Fe2O3 Nanocrystal Moniliforme-Shape Straight-Chains.

Author

Meng, L-r, Chen, Weimeng, Chen, Chinping, Zhou, Heping, Peng, Qing, and Li, Yadong

Subjects
*NANOPARTICLE synthesis, *SINGLE crystals, *CRYSTAL structure
Abstract

Highly uniform coalescent moniliforme-shape α-Fe2O3 straight nanochains built up of single crystal building blocks are synthesized via a facile one-pot solution-phase route at 180 °C using FeCl3, which have interesting magnetic behaviors based on their unique structure. Surprisingly, an exceptionally high TM (Morin transition temperature) is observed. Highly uniform coalescent moniliforme-shape α-Fe2O3 straight nanochains built up of single crystal building blocks are synthesized via a facile one-pot solution-phase route at 180 °C using FeCl3, which have interesting magnetic behaviors based on their unique structure. [ABSTRACT FROM AUTHOR]

Published
2010
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28. Selective Synthesis of Peapodlike Ni/Ni3S2Nanochains and Nickel Sulfide Hollow Chains and Their Magnetic Properties

Author

Zhou, Wei, Chen, Weimeng, Nai, Jianwei, Yin, PengGang, Chen, Chinping, and Guo, Lin

Abstract

Peapodlike Ni/Ni3S2chains of about 30 nm in outer diameter, with Ni cores of 10–15 nm, can be synthesized by a sacrificial template route. The Ni3S2shell exhibits paramagnetic properties with a mass susceptibility of χ≈ 5 × 10−5emu (gOe)−1, while the ferromagnetic Ni cores show a superparamagnetic behavior with a blocking temperature of TB≈ 130 K. The shape anisotropy of the chainlike structure is determined as 5.0 × 104J·m−3, which is larger than the bulk magnetocrystalline anisotropy by one order of magnitude. The demagnetization factor is determined as ΔN= 0.29. The sample provides an ideal structure for studying the magnetization reversal property by the chain‐of‐sphere model. The observations on the formation of the peapod structure verify a growth mechanism of the nanoscale Kirkendall effect. Based on the preparation of peapod chains, a series of nickel sulfide hollow chains with average diameters of 25, 50, and 100 nm are fabricated. In addition, the phase transition for hollow chains from Ni3S2to NiS is studied.

Published
2010
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29. One-Dimensional Chainlike Arrays of Fe3O4 Hollow Nanospheres Synthesized by Aging Iron Nanoparticles in Aqueous Solution

Author

Huang, Jing, Chen, Weimeng, Zhao, Wei, Li, Yaoqi, Li, Xingguo, and Chen, Chinping

Abstract

One-dimensional (1D) chainlike arrays of hollow magnetic Fe3O4spheres have been prepared by simply aging magnetically preassembled Fe nanoparticles in aqueous solution at room temperature. The diameter of the 1D nanomaterials is about 100−200 nm, and the length is up to 1−3 μm, observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The structure and magnetic properties of the Fe3O4hollow chains were characterized by X-ray powder diffraction (XRD) and via a superconducting quantum interference device (SQUID) magnetometer. Mechanism investigations on the time dependent process reveal these hollow nanostructures were formed based on the nanoscale Kirkendall effect. Besides the aqueous microenvironment, the partial pressure of oxygen is of great importance in the formation of 1D chainlike Fe3O4hollow nanostructures.

Published
2009
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