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Synthesis and characterization of cobalt ferrite spinel nanoparticles doped with erbiumCripps, Chala Ann 05 1900 (has links)
No description available.
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Synthesis, structural and magnetic properties of bulk and nanosized (Zn, Cd, Cu)0.5Ni0.5Fe2o4 and NiFe204 ferritesJanuary 2007 (has links)
We present a study of the synthesis, structural and magnetic properties of
bulk and nanosized (Zn, Cd, Cu)0:5Ni0:5Fe2O4 and NiFe2O4 compounds. The
e®ects of electronic con¯guration and atomic sizes of Zn, Cd, Cu and Ni on
the magnetic properties of the ferrites are the primary focus of the study.
Di®erent synthesis routes, preparation conditions and how they a®ect single
phase formation are explored.
The synthesis was undertaken by solid{state reaction, combustion, hydrothermal
and glycothermal techniques. The structure determination was by Xray
di®raction. The magnetic measurements were performed using MÄossbauer
spectroscopy (from 79 K to about 850 K) and a vibrating sample magnetometer
(at about 300 K). The bulk densities of the sintered pellets were deduced
by Archimedes principle. The bulk oxides were produced by solid{state reaction
and combustion techniques. Fine powders with grain sizes of about 10
nm were produced from bulk compounds by a Retsch planetary ball mill and
by the hydrothermal and glycothermal processes. The e®ects of the applied
pressure used to make pellets (related to green density of the raw pellets) and
the sintering temperature on the properties were investigated.
An anomalous variation of bulk densities of (Zn, Cd)0:5Ni0:5Fe2O4 oxides
with increase in pelletizing pressure was observed which appears to suggest evidence
for trapped porosity. Di®erent states of pelletizing the samples appear
to be related to a systematic change of the hyper¯ne ¯eld distributions derived
from the MÄossbauer spectra. The temperature dependence of the magnetic hyper
¯ne ¯elds at tetrahedral (A) and octahedral (B) sites were observed to vary
with temperature according to the equations Bhf (T) = Bhf (0)[1 ¡ (T=TC)n]¯n
where n = 1 (based on the Landau{Ginzburg theory) and n = 2 (based on the
Stoner theory). The equation Bhf (T) = Bhf (0)[1¡(T=TC)2]¯2 appears to ¯t the
hyper¯ne ¯eld data over a wider temperature range. The Zn{ and Cd{based
oxides were found to be ferrimagnetic with Curie temperature TC = 548 § 3 K (measured by zero velocity technique). The Cu{based compound exhibited antiferromagnetic
behavior with a magnetic transition temperature of 825 § 3 K.
The di®erence in behavior between Zn{, Cd{ and Cu{based compounds is due
to di®erence in electronic con¯guration and atomic or ionic sizes. The stronger
magnetic coupling between spins in the Cu{based sample can be explained by
the presence of RKKY interactions in addition to superexchange interactions.
The larger ionic size for Cd appears to favour smaller grain sizes in Cd{based
oxides. An anomalous increase in TC is obtained in the Zn0:5Ni0:5Fe2O4 compound
with reduction in grain size. This increase in TC is attributed to a
distribution of Zn ions on both A and B sites.
The MÄossbauer spectra of the milled nanosized samples show a combination
of ferrimagnetic and paramagnetic behavior. The coercive ¯eld (HC) at room
temperature was found to increase with reduction in grain size (G) according to
the equation HC = am+bm=G, which is consistent with multidomain particles.
With further reduction in grain sizes, the coercive ¯eld reduced according to the
equation HC = as ¡bs=G2. This equation is associated with the onset of single
domain particles. The samples produced by hydrothermal and glycothermal
processes show evidence of transformation from single domain to multidomain
structure with increasing sintering temperature.
The ease of single{phase formation in the compounds studied is shown to
depend on the technique used to prepare the samples. Single phase formation of
the spinel structure was easier to achieve in samples prepared by wet chemical
methods because lower sintering temperatures (T < 1000 oC) were required. / Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2007.
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Synthesis, magnetic and electrical characterizations of nanoparticle ferrites.Abdallah, Hafiz Mohammed Ibrahim. January 2012 (has links)
The synthesis, structure and physical properties of a series of Mnx(Co, Mg)₁ˍxFe₂O₄,
(Mg, Sr)₀.₂ Mn₀.₁Co₀.₇Fe₂O₄ and Mg₀.₅Mn₀.₅(RE)₀.₁Fe₁.₉O₄ (where RE are rare earth
elements) nanoferrites have been studied. These compounds were synthesized at low
reaction temperature of about 200 ⁰C using the glycol-thermal method. The starting
materials were high-purity metal chlorides or nitrates which were precipitated by
NH₄OH and KOH respectively. In addition, MnxCo₁₋xFe₂O₄ (x = 0, 0.5 and 1)
samples were produced directly from high-purity metal oxides by high-energy ball
milling technique. Single-phase cubic spinel structure and nanoparticle structure of
the synthesized samples were confirmed by X-ray diffraction (XRD) and transmission
electron microscope (TEM). The results show that the produced powders of the asprepared
samples have average grain sizes ranging from 7 to 16 nm. Filtering the
precipitates by Whatman glass microfiber filters (GF/F) appears to be important in
obtaining the small particle sizes. We suspect higher stability of the MnxCo₁₋xFe₂O₄
at x = 0 and 0.5 where complete symmetry in the proportion of the atoms on
tetrahedral (A) and octahedral (B) sites would tend to favour larger nanoparticles.
The evolutions of the magnetic properties as a function of composition, annealing
temperature under air and argon atmospheres or measuring temperature have
been investigated by ⁵⁷Fe Mössbauer spectroscopy, vibration sample magnetometer
(VSM) and superconducting quantum interference device (SQUID). Significant
changes in magnetic properties are observed across the composition ranges studied.
The Mössbauer spectra indicate ferrimagnetic, superparamagnetic and paramagnetic
behaviours of the compounds. The results show evidence of transformation
from single-domain to multi-domain structure with thermal annealing in
our samples. Temperature dependence of magnetization shows differences between
field cooling (FC) and zero field cooling (ZFC) which we attribute to spin-freezing
and thermal relaxation for typical nanoparticles. Significant increase in coercive
field with reduction in measuring temperature is obtained in Co- based compounds.
Mn₀.₅Co₀.₅Fe₂O₄, Sr₀.₂Mn₀.₁Co₀.₇Fe₂O₄ and Mg₀.₂Mn₀.₁Co₀.₇Fe₂O₄ have large coercive
fields of 1.45, 3.02 and 10.70 kOe at 4 K compared to 0.17, 0.05 and 0.05 kOe
at room temperature respectively. Variation of coercive fields (Hc) with measuri
ing temperature for MnxCo₁₋xFe₂O₄ (x = 0.1 and 0.05), (Mg, Sr)₀.₂Mn₀.₁Co₀.₇Fe₂O₄
nanoferrites follow the Kneller's law for uniaxial non-interacting single domain particles
of the form Hc(T) = Hc(0)[1-( T/Tβ)α]. The observed temperature dependences
are consistent with α = 1/2. We also find evidence of the departure from this law
at lower temperature. The temperature dependence of the saturation magnetizations
were observed to vary with temperature according to the modified Bloch's
law Ms(T) = Ms(0)[1 - ( T/T₀)ᵝ] where β is at least 1.5. This is attributed to the
confinement effects of the spin-wave spectrum for magnetic clusters. The equation
appears to fit the saturation magnetization data over the entire temperature range
with values of β from 2.1 to 2.4 for the samples studied. These results are consistent
with the nanoparticle nature of the compounds.
In Mg₀.₅Mn₀.₅(RE)₀.₁Fe₁.₉O₄ nanoferrites, the grain sizes, lattice parameters and
saturation magnetizations increase with RE substitution which we attribute to larger
RE ions substituting smaller Fe ions. The results show evidence of superparamagnetic
behaviour of the nanoparticles. The highest grain size and magnetizations are
obtained for the Gd substituted sample. We find strong correlation between the saturation
magnetizations, grain sizes and microstrains with de Gennes factor G. The
correlation with grain sizes and microstrains appear to be unique and characteristic
of the nanoparticle nature of the compounds.
Bulk samples in the form of pellets were also produced from the as-prepared
samples of MnxCo₁₋xFe₂O₄ for resistivity measurements. The temperature dependence
of the electrical resistivity for samples sintered from 600 - 1100 ⁰C under
argon atmosphere were studied using the four-probe method from room temperature
to about 110 ⁰C. Two possible mechanisms for resistivity involving Tˉ¹ and
Tˉ¹/² dependences were investigated which we associated with semiconducting and
inter-grain conductivity respectively. The Tˉ¹/² dependence is found to fit the data
better and predicts higher activation energies. The resistivity was observed to be
sensitive to the surface of the pellet being probed and the annealing temperature. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2012.
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The design and synthesis of bridging para-dioxolenes : towards functional metallosupramolecular structuresCaldwell, Sharon Lindsay 10 March 2010 (has links)
A series of para-dioxolene bridging ligands with bis-tridentate or bis-bidentate coordination pockets have been prepared. These ligands were designed to serve as building blocks in the preparation of functional metallosupramolecular structures.
The bis-tridentate dipyridyl-diazaanthraquinones have topologies suitable for the preparation of [2 x 2] grids or larger extended structures. Employing a double condensation reaction between 1,3-diamino-4,6-benzenedicarboxaldehyde and 2-acetyl pyridine successfully afforded a cisoid binding diazaanthraquinone. The redox activity of the latter revealed it is more easily reduced than structurally similar 1,5- and 1,8-diazaanthraquinones. The synthesis of an analogous ligand displaying transoid coordination pockets proved challenging. Several approaches were attempted however the preparation of key intermediates 1,4-dinitro-2,5-benzenedicarboxaldehyde and 2,5-diamino-1,4-(hydroxyI-methyl) benzene were unsuccessful.
A collection of bis-bidentate 2,5-bis(phosphino)1,4-dioxolenes were prepared with diphenyl, diisopropyl and diethoxy substituents at the phosphorus center. 2,5-
Dibromo-1,4-dimethoxybenzene was reacted with the appropriate chlorophosphine under lithiation conditions to afford the dimethoxy compound, which was subsequently deprotected to the hydroquinone state with a Lewis acid. The diphenylphosphino hydroquinone was oxidized using phenyliodonium bisacetate, however efforts to oxidize other hydroquinone precursors to the targeted quinone state proved challenging. Diphenyl and diisopropyl phosphino hydroquinones were successfully coordinated with diamagnetic palladium hexafluoroacetylacetonate precursors. The resulting bimetallic bis(phosphino) dianion complexes were subsequently oxidized to the semiquinone state using silver (I) hexafluorophosphate and studied to determine the distinctive features of the semiquinone ligand.
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Development of synthesis method for spinel ferrite magnetic nanoparticle and its superparamagnetic propertiesHan, Man Huon 25 August 2008 (has links)
The magnetic spinel ferrite nanoparticle is exceptionally intriguing nanocrystal system due to the industrial importance of various technical applications and the scientific significance of studying the quantum origin of magnetism. Studies of quantum influences upon magnetic properties have revealed that the spin-orbit coupling and the net magnetization greatly affect the net magnetic properties of each spinel ferrite system differently. In case of cobalt ferrite where spin-orbit coupling is relatively large, increasing Cr3+ doping concentration, which has smaller magnetic moment and zero angular moment, decreases blocking temperature, saturation magnetization, remnant magnetization and coercivity. However, in case of manganese ferrite where spin-orbit coupling is relatively small, increasing Cr3+ doping concentration, reduces all the magnetic parameters except coercivity. The coercivity increases due to smaller magnetocrystalline anisotropy energy constant which forces the coercivity to increase as saturation magnetization decreases in accordance with Stoner-Wohlfarth theory. In order to improve product quality and quantity, synthesis routes in hot oleylamine and aminolytic reaction were developed. Both methods were proven to be extremely effective, environmental friendly, inexpensive, and simple routes in the synthesis of a variety of spinel ferrite systems including CoFe2O4, MnFe2O4, NiFe2O4, and ZnFe2O4 from a single source metal precursor.
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Magnetic ordering of erbium and uranium nickel(2) silicon(2) by neutron scattering.Lin, Hong. Collins, M.F. Unknown Date (has links)
Thesis (Ph.D.)--McMaster University (Canada), 1991. / Source: Dissertation Abstracts International, Volume: 54-02, Section: B, page: 0847.
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Novel magnetic composites for high frequency applications /Zhang, Xiaokai. January 2009 (has links)
Thesis (Ph.D.)--University of Delaware, 2009. / Principal faculty advisor: John Q. Xiao, Dept. of Physics and Astronomy. Includes bibliographical references.
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Small angle neutron scattering studies of magnetic recording media /Wismayer, Matthew P. January 2008 (has links)
Thesis (Ph.D.) - University of St Andrews, March 2008.
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Novel superparamagnetic nanoparticles as MRI contrast agents /Bárcena, Carlos, January 2008 (has links)
Thesis (Ph.D.)--University of Texas at Dallas, 2008. / Includes vita. Includes bibliographical references.
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Characterization of high spin molecular magnetsStowe, Ashley Clinton. Dalal, Naresh. Van Tol, Johan. January 2004 (has links)
Thesis (Ph. D.)--Florida State University, 2004. / Advisors: Dr. Naresh Dalal, Dr. Johan van Tol, Florida State University, Arts and Sciences, Dept. of Chemistry and Biochemistry. Title and description from dissertation home page (viewed Jan. 18, 2005). Includes bibliographical references.
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