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Spin polarization and quantum spins in Au nanoparticles.

Li CY, Karna SK, Wang CW, Li WH - Int J Mol Sci (2013)

Bottom Line: The results show that the maximum particle moment will appear in 2.4 nm Au particles.A similar result of the maximum saturation magnetization appearing in 2.3 nm Au particles is also concluded through analysis of the dependency of the saturation magnetization M(P) on particle size.The M(P)(d) curve departs significantly from the 1/d dependence, but can be described by a log-normal function.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics and Center for Neutron Beam Applications, National Central University, Jhongli 32001, Taiwan. chiyenli@alumni.ncu.edu.tw

ABSTRACT
The present study focuses on investigating the magnetic properties and the critical particle size for developing sizable spontaneous magnetic moment of bare Au nanoparticles. Seven sets of bare Au nanoparticle assemblies, with diameters from 3.5 to 17.5 nm, were fabricated with the gas condensation method. Line profiles of the X-ray diffraction peaks were used to determine the mean particle diameters and size distributions of the nanoparticle assemblies. The magnetization curves M(H(a)) reveal Langevin field profiles. Magnetic hysteresis was clearly revealed in the low field regime even at 300 K. Contributions to the magnetization from different size particles in the nanoparticle assemblies were considered when analyzing the M(H(a)) curves. The results show that the maximum particle moment will appear in 2.4 nm Au particles. A similar result of the maximum saturation magnetization appearing in 2.3 nm Au particles is also concluded through analysis of the dependency of the saturation magnetization M(P) on particle size. The M(P)(d) curve departs significantly from the 1/d dependence, but can be described by a log-normal function. Magnetization can be barely detected for Au particles larger than 27 nm. Magnetic field induced Zeeman magnetization from the quantum confined Kubo gap opening appears in Au nanoparticles smaller than 9.5 nm in diameter.

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X-ray diffraction pattern of the Au-74 particle assembly at 300 K, revealing a face centered cubic crystalline structure. The solid curves indicate the calculated pattern assuming a log-normal size distribution with a center at 3.5 nm and a standard deviation width of 0.52. The inset shows the size distributions obtained from the X-ray diffraction profile (solid curve) and from AFM and TEM images (vertical bars).
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f15-ijms-14-17618: X-ray diffraction pattern of the Au-74 particle assembly at 300 K, revealing a face centered cubic crystalline structure. The solid curves indicate the calculated pattern assuming a log-normal size distribution with a center at 3.5 nm and a standard deviation width of 0.52. The inset shows the size distributions obtained from the X-ray diffraction profile (solid curve) and from AFM and TEM images (vertical bars).

Mentions: Size analysis based on the AFM and TEM images reveals the size distributions of the Au NP powders used in the present studies. They can be described using log-normal functions. The X-ray diffraction patterns of all Au NP powders are associated with a face-centered cubic Au structure. As expected, the diffraction peaks appear to be much broader than the instrumental resolution, reflecting the finite-size effect. The mean particle diameters are determined by fitting the diffraction peaks to the diffraction profiles of finite sized particles, assuming a log-normal size distribution as is indicated by the AFM and TEM images. Figure 15 shows the observed (crosses) and fitted (solid curves) X-ray diffraction patterns of the representative Au-74 NP powder at 300 K, where the solid curves indicate the calculated pattern assuming a log-normal size distribution (solid curve in the inset to Figure 15) with a center at 3.5 nm and a standard deviation of 0.52. This size distribution obtained from the XRD peak profiles agrees well with that obtained from the AFM and TEM images (vertical bars) shown in the inset to Figure 15. Chemical analysis by means of XRF and AAS has also been performed on all Au NP powders to search for impurities. The XRF spectra are taken on a Rigaku ZSK Primus II spectrometer, employing the standard setup to scan through ~5 mg of the Au NPs. No fluorescence lines other than those from Au are detected. The AAS spectra are taken on a Perkin-Elmer AAnalyst 700 spectrometer, employing a graphite furnace to atomize ~3 mg of the Au nanoparticles with a cathode discharge lamp used for detecting Fe and Ni. No traces of oxidation phases or elements other than Au may be identified from the XRD/EDXS/XRF/AAS spectra. We estimate the impurity phases in the samples to be less than 20 parts per million. The chamber pressure and heating current employed in fabrication, the mean particle diameters, standard deviations of log-normal size distribution profile and lattice constants for the seven sets of NP powder used in the present study are all listed in Table 1.


Spin polarization and quantum spins in Au nanoparticles.

Li CY, Karna SK, Wang CW, Li WH - Int J Mol Sci (2013)

X-ray diffraction pattern of the Au-74 particle assembly at 300 K, revealing a face centered cubic crystalline structure. The solid curves indicate the calculated pattern assuming a log-normal size distribution with a center at 3.5 nm and a standard deviation width of 0.52. The inset shows the size distributions obtained from the X-ray diffraction profile (solid curve) and from AFM and TEM images (vertical bars).
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC3794745&req=5

f15-ijms-14-17618: X-ray diffraction pattern of the Au-74 particle assembly at 300 K, revealing a face centered cubic crystalline structure. The solid curves indicate the calculated pattern assuming a log-normal size distribution with a center at 3.5 nm and a standard deviation width of 0.52. The inset shows the size distributions obtained from the X-ray diffraction profile (solid curve) and from AFM and TEM images (vertical bars).
Mentions: Size analysis based on the AFM and TEM images reveals the size distributions of the Au NP powders used in the present studies. They can be described using log-normal functions. The X-ray diffraction patterns of all Au NP powders are associated with a face-centered cubic Au structure. As expected, the diffraction peaks appear to be much broader than the instrumental resolution, reflecting the finite-size effect. The mean particle diameters are determined by fitting the diffraction peaks to the diffraction profiles of finite sized particles, assuming a log-normal size distribution as is indicated by the AFM and TEM images. Figure 15 shows the observed (crosses) and fitted (solid curves) X-ray diffraction patterns of the representative Au-74 NP powder at 300 K, where the solid curves indicate the calculated pattern assuming a log-normal size distribution (solid curve in the inset to Figure 15) with a center at 3.5 nm and a standard deviation of 0.52. This size distribution obtained from the XRD peak profiles agrees well with that obtained from the AFM and TEM images (vertical bars) shown in the inset to Figure 15. Chemical analysis by means of XRF and AAS has also been performed on all Au NP powders to search for impurities. The XRF spectra are taken on a Rigaku ZSK Primus II spectrometer, employing the standard setup to scan through ~5 mg of the Au NPs. No fluorescence lines other than those from Au are detected. The AAS spectra are taken on a Perkin-Elmer AAnalyst 700 spectrometer, employing a graphite furnace to atomize ~3 mg of the Au nanoparticles with a cathode discharge lamp used for detecting Fe and Ni. No traces of oxidation phases or elements other than Au may be identified from the XRD/EDXS/XRF/AAS spectra. We estimate the impurity phases in the samples to be less than 20 parts per million. The chamber pressure and heating current employed in fabrication, the mean particle diameters, standard deviations of log-normal size distribution profile and lattice constants for the seven sets of NP powder used in the present study are all listed in Table 1.

Bottom Line: The results show that the maximum particle moment will appear in 2.4 nm Au particles.A similar result of the maximum saturation magnetization appearing in 2.3 nm Au particles is also concluded through analysis of the dependency of the saturation magnetization M(P) on particle size.The M(P)(d) curve departs significantly from the 1/d dependence, but can be described by a log-normal function.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics and Center for Neutron Beam Applications, National Central University, Jhongli 32001, Taiwan. chiyenli@alumni.ncu.edu.tw

ABSTRACT
The present study focuses on investigating the magnetic properties and the critical particle size for developing sizable spontaneous magnetic moment of bare Au nanoparticles. Seven sets of bare Au nanoparticle assemblies, with diameters from 3.5 to 17.5 nm, were fabricated with the gas condensation method. Line profiles of the X-ray diffraction peaks were used to determine the mean particle diameters and size distributions of the nanoparticle assemblies. The magnetization curves M(H(a)) reveal Langevin field profiles. Magnetic hysteresis was clearly revealed in the low field regime even at 300 K. Contributions to the magnetization from different size particles in the nanoparticle assemblies were considered when analyzing the M(H(a)) curves. The results show that the maximum particle moment will appear in 2.4 nm Au particles. A similar result of the maximum saturation magnetization appearing in 2.3 nm Au particles is also concluded through analysis of the dependency of the saturation magnetization M(P) on particle size. The M(P)(d) curve departs significantly from the 1/d dependence, but can be described by a log-normal function. Magnetization can be barely detected for Au particles larger than 27 nm. Magnetic field induced Zeeman magnetization from the quantum confined Kubo gap opening appears in Au nanoparticles smaller than 9.5 nm in diameter.

Show MeSH
Related in: MedlinePlus