The Master of Physics Degree
defense for Narayan Poudyal was held on August 5, 2005. The title
for the Master's thesis is "Synthesis and Characterization of Magnetic
Nanoparticles". The abstract is given as below:
Synthesis of
uniform nanoparticles (<100 nm)
of hard and soft magnetic materials have attracted much attention in
last two decades because of their unique magnetic properties and
potential for many applications such as high density recording media,
biotechnology, ferrofluids, and fabrication of exchange-coupled
nanocomposite permanent magnets. In this study, synthesis and
characterization of hard (FePt) and soft (Fe3O4
and CoFe2O4) magnetic nanoparticles with different
size is reported. Monodisperse FePt, Fe3O4 and
CoFe2O4 nanoparticles were synthesized by chemical
solution methods. Particle diameter was tuned from 3 to 20 nm by varying
reaction conditions or by seed-mediated growth method. Monodisperse
face-centered tetragonal (fct) FePt nanoparticles in NaCl matrix to
convert the fcc particles into ordered fct structure.
Morphological, structural , and compositional characterization of the
nanoparticles were performed by Transimission Electron Microscope (TEM),
High resolution TEM (HRTEM). Laser Particles-Size Analyzer, X-ray
Diffractometer (XRD), Energy Dispersive X-ray (EDX), and Inductively
Coupled Plasma (ICP). Magnetic properties of nanoparticles of different
sizes at different temperatures were studied by Anternating Gradient
Magnetometer (AGM), Superconducting Quantum Interference Device (SQUID),
and Mössbauer Spectroscope. It has been found
that all the as-synthesized Fe3O4 nanoparticles up
to 20 nm were found to be superparamagnetic at room temperature while
CoFe2O4 nanoparticles larger than 12 nm were
ferromagnetic. An exchange bias field up to 3 kOe was observed for 3 nm
CoFe2O4 nanoparticles in field cooling
measurements. Very high coercivity of the isolated fct FePt
nanoparticles up to 30 kOe at room temperature has been obtained.
Interesting experimental results on the size dependent magnetic
properties for both hard and soft magnetic nanoparticles at different
temperatures have been found.
