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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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Temperature dependence of the induced saturation magnetization MZ of the 6.5 nm Au-78 assembly. The solid line indicates the results of fits for the expression listed in the plot, giving an average level separation of Δ = 3.13 meV.
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f9-ijms-14-17618: Temperature dependence of the induced saturation magnetization MZ of the 6.5 nm Au-78 assembly. The solid line indicates the results of fits for the expression listed in the plot, giving an average level separation of Δ = 3.13 meV.

Mentions: The variations of MZ with temperature are shown in Figure 9. Thermal reductions of MZ are linked to the creations of thermal magnons. The noticeable drops of MZ upon warming at low temperatures indicate a small energy for the associated thermal magnons. In addition, the valence electrons can also contribute to MZ at finite temperatures, as shown in Figure 4(2). This takes the form of NvμB exp (−Δ/kBT) BJ(y), where NV is the total number of valence electrons. Accounting for the contributions from the conduction and valence electrons and taking the thermal fluctuations of MZ as being proportional to the number of thermal magnons, the induced magnetization takes the form of


Spin polarization and quantum spins in Au nanoparticles.

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

Temperature dependence of the induced saturation magnetization MZ of the 6.5 nm Au-78 assembly. The solid line indicates the results of fits for the expression listed in the plot, giving an average level separation of Δ = 3.13 meV.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f9-ijms-14-17618: Temperature dependence of the induced saturation magnetization MZ of the 6.5 nm Au-78 assembly. The solid line indicates the results of fits for the expression listed in the plot, giving an average level separation of Δ = 3.13 meV.
Mentions: The variations of MZ with temperature are shown in Figure 9. Thermal reductions of MZ are linked to the creations of thermal magnons. The noticeable drops of MZ upon warming at low temperatures indicate a small energy for the associated thermal magnons. In addition, the valence electrons can also contribute to MZ at finite temperatures, as shown in Figure 4(2). This takes the form of NvμB exp (−Δ/kBT) BJ(y), where NV is the total number of valence electrons. Accounting for the contributions from the conduction and valence electrons and taking the thermal fluctuations of MZ as being proportional to the number of thermal magnons, the induced magnetization takes the form of

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