Limits...
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

Mechanism of four-magnon excitation. (a) Growth temperature TA dependence of the E4 M peak, (b) evolution of the scattering factor E4 M/E2 M at various growth temperatures TA. There is no obvious change observed in the growth temperature dependence TA of R and a lowest state is obtained around R = 20/11 in this study. (c) Schematic plot of three possible four-spin deviations in the Ising states at sites connected by strong superexchange interactions in a simple cubic lattice. The circles indicate sites; the number gives the number of spin deviations at each site, while the linkages denote an exchange interaction between next-nearest-neighbor sites.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3211999&req=5

Figure 9: Mechanism of four-magnon excitation. (a) Growth temperature TA dependence of the E4 M peak, (b) evolution of the scattering factor E4 M/E2 M at various growth temperatures TA. There is no obvious change observed in the growth temperature dependence TA of R and a lowest state is obtained around R = 20/11 in this study. (c) Schematic plot of three possible four-spin deviations in the Ising states at sites connected by strong superexchange interactions in a simple cubic lattice. The circles indicate sites; the number gives the number of spin deviations at each site, while the linkages denote an exchange interaction between next-nearest-neighbor sites.

Mentions: The weak and broad peak at 323.6 meV is assigned to the four-magnon excitation of NiO nanowalls (marked as 4 M) and presented in Figure 9a. As TA is decreased from 800°C to 400°C, the 4 M peak shifts to a lower energy and broaden as a results of the nanosized effect. Moreover, the ratio of the growth temperature TA dependence of the four-magnon states to the two-magnon states gives a scattering factor value of R = E4 M/E2 M, as shown in Figure 9b and Table 5. This can be used as an indicator of the four-magnon configuration from the lowest to higher states. In general, the Ising calculation is used for prediction in a lot of four-magnon models, such as the lowest state of 20J2 (D = 3) and four higher states of 21J2 (D = 3), 22J2 (D = 3), 23J2 (D = 2), and 24J2 (D = 3), where D is the degeneracy. The related theoretical scattering factors R with corresponding four-magnon configurations are plotted in to Figure 9b, where the lowest two-magnon energy used in the calculation is 11J2. There is no obvious change observed in the growth temperature dependence TA of R and a lowest state is obtained around R = 20/11 in this study. Three out of four possible magnon models at lowest state, proposed in principle by the Ising model plus second-order perturbation theory [37], are shown in Figure 9c. A schematic plot of the three possible four-spin deviation Ising states on sites were connected by strong superexchange interactions in a simple cubic lattice. The circles indicate sites; the number gives the number of spin deviations on each site. The linkages denote an exchange interaction where the sites are next-nearest-neighbor. The differences between the experimental and theoretical results can be explained by neglecting the weak ferromagnetic coupling and constant J2 for all compositions in the system. The finite size effect and nickel vacancy dependence of the Raman phonon-magnon modes most likely play the dominant role affecting the Raman shifts that lead to unusual properties in NiO nanowalls.


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)

Mechanism of four-magnon excitation. (a) Growth temperature TA dependence of the E4 M peak, (b) evolution of the scattering factor E4 M/E2 M at various growth temperatures TA. There is no obvious change observed in the growth temperature dependence TA of R and a lowest state is obtained around R = 20/11 in this study. (c) Schematic plot of three possible four-spin deviations in the Ising states at sites connected by strong superexchange interactions in a simple cubic lattice. The circles indicate sites; the number gives the number of spin deviations at each site, while the linkages denote an exchange interaction between next-nearest-neighbor sites.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 9: Mechanism of four-magnon excitation. (a) Growth temperature TA dependence of the E4 M peak, (b) evolution of the scattering factor E4 M/E2 M at various growth temperatures TA. There is no obvious change observed in the growth temperature dependence TA of R and a lowest state is obtained around R = 20/11 in this study. (c) Schematic plot of three possible four-spin deviations in the Ising states at sites connected by strong superexchange interactions in a simple cubic lattice. The circles indicate sites; the number gives the number of spin deviations at each site, while the linkages denote an exchange interaction between next-nearest-neighbor sites.
Mentions: The weak and broad peak at 323.6 meV is assigned to the four-magnon excitation of NiO nanowalls (marked as 4 M) and presented in Figure 9a. As TA is decreased from 800°C to 400°C, the 4 M peak shifts to a lower energy and broaden as a results of the nanosized effect. Moreover, the ratio of the growth temperature TA dependence of the four-magnon states to the two-magnon states gives a scattering factor value of R = E4 M/E2 M, as shown in Figure 9b and Table 5. This can be used as an indicator of the four-magnon configuration from the lowest to higher states. In general, the Ising calculation is used for prediction in a lot of four-magnon models, such as the lowest state of 20J2 (D = 3) and four higher states of 21J2 (D = 3), 22J2 (D = 3), 23J2 (D = 2), and 24J2 (D = 3), where D is the degeneracy. The related theoretical scattering factors R with corresponding four-magnon configurations are plotted in to Figure 9b, where the lowest two-magnon energy used in the calculation is 11J2. There is no obvious change observed in the growth temperature dependence TA of R and a lowest state is obtained around R = 20/11 in this study. Three out of four possible magnon models at lowest state, proposed in principle by the Ising model plus second-order perturbation theory [37], are shown in Figure 9c. A schematic plot of the three possible four-spin deviation Ising states on sites were connected by strong superexchange interactions in a simple cubic lattice. The circles indicate sites; the number gives the number of spin deviations on each site. The linkages denote an exchange interaction where the sites are next-nearest-neighbor. The differences between the experimental and theoretical results can be explained by neglecting the weak ferromagnetic coupling and constant J2 for all compositions in the system. The finite size effect and nickel vacancy dependence of the Raman phonon-magnon modes most likely play the dominant role affecting the Raman shifts that lead to unusual properties in NiO nanowalls.

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