Studying dynamics of magnetization relaxation in excited magnetic materials is
important both for understanding the rates and pathways of magnetization relaxation and
for the potential use in spin-based electronics and data storage devices in the future.
Previous studies have demonstrated that the size of nanocrystals is an important factor
for energy relaxation in quantum dots and metal nanoparticles. Since magnetization
relaxation is one of energy relaxation pathways, the size of nanocrystals may be also an
important factor for magnetization relaxation in nanoscale magnetic materials. The goal
of this study is to have a better understanding of magnetization relaxation in nanoscale
magnetic materials. In particular, we focused on the correlation between the nanocrystal
size and the rates of spin-lattice relaxation (SLR), a magnetization relaxation pathway, in
magnetic nanocrystals.
The size-dependent magnetization relaxation rate after optically induced
demagnetization in colloidal Fe3O4 nanocrystals was measured by using time-resolved
Faraday rotation (FR). Fe3O4 nanocrystals were chosen as the model system to study the correlation between the size of nanocrystals and the rates of SLR due to the wellestablished
synthetic procedure of making nanocrystals with various sizes and narrow
size dispersion. Faster SLR rates were observed in smaller Fe3O4 nanocrystals. The
results suggested the surface of nanocrystals have higher efficiency of SLR than the
interior region by using a simple model to analyze the SLR rates of Fe3O4 nanocrystals
with various sizes. Higher efficiency of SLR at the surface may be due to the stronger
spin-orbit coupling at the surface relative to the interior region. In addition to
magnetization dynamics studies, the effect of oxidation on static FR in iron oxide
nanocrystals (between Fe3O4 and y-Fe2O3) was studied. The results indicated FR signal
is linearly correlated to the strength of optical transition between Fe2 and Fe3 in Fe3O4
for a given size of nanocrystals.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2010-08-8304 |
| Date | 2010 August 1900 |
| Creators | Hsia, Chih-Hao |
| Contributors | Son, Dong Hee |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | thesis, text |
| Format | application/pdf |
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