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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

The growth temperature TA dependence of Raman patterns. (a) Two-dimensional map of the intensity and TA dependence of Raman patterns taken at room temperature. A selected Raman pattern taken at TA = 500°C is shown at the top, revealing a series of phonon modes and magnon excitations. (b) The growth temperature TA dependence of the integrated intensity in the 2LO and (c) LO mode.
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Figure 7: The growth temperature TA dependence of Raman patterns. (a) Two-dimensional map of the intensity and TA dependence of Raman patterns taken at room temperature. A selected Raman pattern taken at TA = 500°C is shown at the top, revealing a series of phonon modes and magnon excitations. (b) The growth temperature TA dependence of the integrated intensity in the 2LO and (c) LO mode.

Mentions: Figure 7a shows the series of Raman spectra (in the bottom of the milli-electron-volt unit and top of the per-centimeter unit) taken at room temperature for annealing temperatures ranging from 400 to 800°C. Two typical one-phonon (TO and LO modes) and two-phonon (2TO, TO + LO, and 2LO modes) excitations were observed at TA = 500°C (shown at the top of Figure 7a), and are in good agreement with the values reported for bulk NiO single crystals [37]. The growth temperature TA dependence of the phonon and two-magnon peak positions and intensities obtained from two-dimensional Raman images of NiO nanowalls are shown at the bottom of Figure 7a. Here, different colors are used to differentiate the peak intensity of the Raman patterns after TA = 400°C to 800°C. As indicated on the bottom of Figure 7a, there is one-phonon peak at ELO = 66.1(1) meV, corresponding to the LO mode and decreasing with increasing TA. After TA is increased to 500°C, we observed two significant broader peaks around E2LO = 136.7(5) and 180.7(2) meV, respectively, which are associated with the 2LO and two-magnon modes and increase as TA increases. The anomalous behaviors can be analyzed quantitatively using the profile fitting method. These peaks, including the phonon and two-magnon modes, were analyzed by the Voigt function covering the whole regime. The detailed TA dependences of the peak position and full widths at half maximum (FWHM) are listed in Table 4. Figure 7b shows the TA dependence of the integrated intensity of the selected peak for the 2LO mode. As the growth temperature TA is reduced, the integrated intensity of the 2LO mode rapidly decreases at around TA = 400°C, signaling the finite size effect, which acts to confine the lattice vibration in corroboration with the strength of two-phonon coupling. Figure 7c shows that the integrated intensity increases in the single phonon LO mode with decreasing TA, in comparison with that in two-phonon 2LO mode. The enhancement of intensity that occurs at lower growth temperatures is due to parity-breaking defects, since the concentration of nickel vacancies is high, as can be quantitatively investigated through two-magnon Raman scattering.


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)

The growth temperature TA dependence of Raman patterns. (a) Two-dimensional map of the intensity and TA dependence of Raman patterns taken at room temperature. A selected Raman pattern taken at TA = 500°C is shown at the top, revealing a series of phonon modes and magnon excitations. (b) The growth temperature TA dependence of the integrated intensity in the 2LO and (c) LO mode.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 7: The growth temperature TA dependence of Raman patterns. (a) Two-dimensional map of the intensity and TA dependence of Raman patterns taken at room temperature. A selected Raman pattern taken at TA = 500°C is shown at the top, revealing a series of phonon modes and magnon excitations. (b) The growth temperature TA dependence of the integrated intensity in the 2LO and (c) LO mode.
Mentions: Figure 7a shows the series of Raman spectra (in the bottom of the milli-electron-volt unit and top of the per-centimeter unit) taken at room temperature for annealing temperatures ranging from 400 to 800°C. Two typical one-phonon (TO and LO modes) and two-phonon (2TO, TO + LO, and 2LO modes) excitations were observed at TA = 500°C (shown at the top of Figure 7a), and are in good agreement with the values reported for bulk NiO single crystals [37]. The growth temperature TA dependence of the phonon and two-magnon peak positions and intensities obtained from two-dimensional Raman images of NiO nanowalls are shown at the bottom of Figure 7a. Here, different colors are used to differentiate the peak intensity of the Raman patterns after TA = 400°C to 800°C. As indicated on the bottom of Figure 7a, there is one-phonon peak at ELO = 66.1(1) meV, corresponding to the LO mode and decreasing with increasing TA. After TA is increased to 500°C, we observed two significant broader peaks around E2LO = 136.7(5) and 180.7(2) meV, respectively, which are associated with the 2LO and two-magnon modes and increase as TA increases. The anomalous behaviors can be analyzed quantitatively using the profile fitting method. These peaks, including the phonon and two-magnon modes, were analyzed by the Voigt function covering the whole regime. The detailed TA dependences of the peak position and full widths at half maximum (FWHM) are listed in Table 4. Figure 7b shows the TA dependence of the integrated intensity of the selected peak for the 2LO mode. As the growth temperature TA is reduced, the integrated intensity of the 2LO mode rapidly decreases at around TA = 400°C, signaling the finite size effect, which acts to confine the lattice vibration in corroboration with the strength of two-phonon coupling. Figure 7c shows that the integrated intensity increases in the single phonon LO mode with decreasing TA, in comparison with that in two-phonon 2LO mode. The enhancement of intensity that occurs at lower growth temperatures is due to parity-breaking defects, since the concentration of nickel vacancies is high, as can be quantitatively investigated through two-magnon Raman scattering.

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