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Growth mechanism and magnon excitation in NiO nanowalls.

Gandhi AC, Huang CY, Yang CC, Chan TS, Cheng CL, Ma YR, Wu SY - Nanoscale Res Lett (2011)

Bottom Line: The nanosized effects of short-range multimagnon excitation behavior and short-circuit diffusion in NiO nanowalls synthesized using the Ni grid thermal treatment method were observed.This study shows that short spin correlation leads to an exponential dependence of the growth temperatures and the existence of nickel vacancies during the magnon excitation.Four-magnon configurations were determined from the scattering factor, revealing a lowest state and monotonic change with the growth temperature.PACS: 75.47.Lx; 61.82.Rx; 75.50.Tt; 74.25.nd; 72.10.Di.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physics, National Dong Hwa University, Hualien 97401, Taiwan. sywu@mail.ndhu.edu.tw.

ABSTRACT
The nanosized effects of short-range multimagnon excitation behavior and short-circuit diffusion in NiO nanowalls synthesized using the Ni grid thermal treatment method were observed. The energy dispersive spectroscopy mapping technique was used to characterize the growth mechanism, and confocal Raman scattering was used to probe the antiferromagnetic exchange energy J2 between next-nearest-neighboring Ni ions in NiO nanowalls at various growth temperatures below the Neel temperature. This study shows that short spin correlation leads to an exponential dependence of the growth temperatures and the existence of nickel vacancies during the magnon excitation. Four-magnon configurations were determined from the scattering factor, revealing a lowest state and monotonic change with the growth temperature.PACS: 75.47.Lx; 61.82.Rx; 75.50.Tt; 74.25.nd; 72.10.Di.

No MeSH data available.


Related in: MedlinePlus

Relation between the annealing temperature TA and the mean nanowall width <d >. The growth temperature TA dependence of the mean nanowall width <d >, where the solid curve shows the fit to the parabolic law and the fitted values.
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Figure 2: Relation between the annealing temperature TA and the mean nanowall width <d >. The growth temperature TA dependence of the mean nanowall width <d >, where the solid curve shows the fit to the parabolic law and the fitted values.

Mentions: The SEM results showed a significant increase in the average NiO nanowall width <d > from 32(1) to 416(18) nm, with a clear dependence on temperature. It is still unclear, however, under which condition grain growth occurs, and whether it is mainly caused by thermal activation or induced by the annealing time. From the macroscopic view, in this present study, the growth temperature of NiO nanowalls was confined to between 400°C and 800°C, which is 0.275 and 0.55 times the melting point of Ni melting (1,453°C), following the parabolic rate law of Wagner's scaling theory [22,23]. Figure 2 shows relation between the annealing temperature TA and the mean nanowall width <d >, where the solid curve indicates the fit to the parabolic law and the fitted values obtained. The phenomenon of NiO nanowall growth following recrystallization at the grain boundaries has been well documented in the previously report [24]. For example, Upadhyay and colleagues [25] studied the effect of sintering temperature on grain boundary character distribution in pure nickel. They report on observations that the grain boundary distribution and grain growth are correlated well with the accompanying microstructural changes. The annealing of the Ni grid led to the oxidation of the surface Ni, resulting in the formation of a polycrystalline nanosized layer of NiO grains at the surface. Diffusion of oxygen into the Ni voids takes place through these microcracks, resulting in the further formation of NiO nanowalls at the boundaries of the grains. A further increase in annealing temperature results in the formation of a nanowall-type structure over the Ni surface. The width of the nanowalls increases with increasing annealing temperature and at a sufficiently high temperature will merge together. The annealing of Ni grid results in the formation of NiO grains at a lower TA and a merged nanowall film at higher growth temperature, respectively.


Growth mechanism and magnon excitation in NiO nanowalls.

Gandhi AC, Huang CY, Yang CC, Chan TS, Cheng CL, Ma YR, Wu SY - Nanoscale Res Lett (2011)

Relation between the annealing temperature TA and the mean nanowall width <d >. The growth temperature TA dependence of the mean nanowall width <d >, where the solid curve shows the fit to the parabolic law and the fitted values.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211999&req=5

Figure 2: Relation between the annealing temperature TA and the mean nanowall width <d >. The growth temperature TA dependence of the mean nanowall width <d >, where the solid curve shows the fit to the parabolic law and the fitted values.
Mentions: The SEM results showed a significant increase in the average NiO nanowall width <d > from 32(1) to 416(18) nm, with a clear dependence on temperature. It is still unclear, however, under which condition grain growth occurs, and whether it is mainly caused by thermal activation or induced by the annealing time. From the macroscopic view, in this present study, the growth temperature of NiO nanowalls was confined to between 400°C and 800°C, which is 0.275 and 0.55 times the melting point of Ni melting (1,453°C), following the parabolic rate law of Wagner's scaling theory [22,23]. Figure 2 shows relation between the annealing temperature TA and the mean nanowall width <d >, where the solid curve indicates the fit to the parabolic law and the fitted values obtained. The phenomenon of NiO nanowall growth following recrystallization at the grain boundaries has been well documented in the previously report [24]. For example, Upadhyay and colleagues [25] studied the effect of sintering temperature on grain boundary character distribution in pure nickel. They report on observations that the grain boundary distribution and grain growth are correlated well with the accompanying microstructural changes. The annealing of the Ni grid led to the oxidation of the surface Ni, resulting in the formation of a polycrystalline nanosized layer of NiO grains at the surface. Diffusion of oxygen into the Ni voids takes place through these microcracks, resulting in the further formation of NiO nanowalls at the boundaries of the grains. A further increase in annealing temperature results in the formation of a nanowall-type structure over the Ni surface. The width of the nanowalls increases with increasing annealing temperature and at a sufficiently high temperature will merge together. The annealing of Ni grid results in the formation of NiO grains at a lower TA and a merged nanowall film at higher growth temperature, respectively.

Bottom Line: The nanosized effects of short-range multimagnon excitation behavior and short-circuit diffusion in NiO nanowalls synthesized using the Ni grid thermal treatment method were observed.This study shows that short spin correlation leads to an exponential dependence of the growth temperatures and the existence of nickel vacancies during the magnon excitation.Four-magnon configurations were determined from the scattering factor, revealing a lowest state and monotonic change with the growth temperature.PACS: 75.47.Lx; 61.82.Rx; 75.50.Tt; 74.25.nd; 72.10.Di.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physics, National Dong Hwa University, Hualien 97401, Taiwan. sywu@mail.ndhu.edu.tw.

ABSTRACT
The nanosized effects of short-range multimagnon excitation behavior and short-circuit diffusion in NiO nanowalls synthesized using the Ni grid thermal treatment method were observed. The energy dispersive spectroscopy mapping technique was used to characterize the growth mechanism, and confocal Raman scattering was used to probe the antiferromagnetic exchange energy J2 between next-nearest-neighboring Ni ions in NiO nanowalls at various growth temperatures below the Neel temperature. This study shows that short spin correlation leads to an exponential dependence of the growth temperatures and the existence of nickel vacancies during the magnon excitation. Four-magnon configurations were determined from the scattering factor, revealing a lowest state and monotonic change with the growth temperature.PACS: 75.47.Lx; 61.82.Rx; 75.50.Tt; 74.25.nd; 72.10.Di.

No MeSH data available.


Related in: MedlinePlus