Artificial Magnetic Materials (AMMs) are a subgroup of metamaterials which are engineered to provide desirable magnetic properties not seen in natural materials. These artificial structures are designed to provide either negative or enhanced positive (higher than one) relative permeability. AMMs with negative permeability are used to develop Single Negative (SNG), or Double Negative (DNG) metamaterials. AMMs with enhanced positive permeability are used to provide magneto-dielectric materials at microwave frequencies where the natural magnetic materials fail to work efficiently. AMMs are realized by embedding metallic resonators in a host dielectric. These inclusions provide desirable magnetic properties near their resonance frequency. Artificial magnetic materials used as SNG, or DNG have many applications such as: sub-wavelength cavity resonators, sub-wavelength parallel-plate wave guides, sub-wavelength cylindrical and spherical core–shell systems, efficient electrically small dipole antennas, super lenses, THz active devices, sensitivity enhancement near-field probes using double and single negative media, and mutual coupling reduction between antennas. On the other hand, artificial magnetic materials used as magneto-dielectrics have other applications in developing enhanced bandwidth efficient miniaturized antennas, low profile enhanced gain antennas using artificial magnetic superstrates, wide band woodpile Electromagnetic Band Gap (EBG) structures, EBGs with enhanced in-phase reflection bandwidth used as artificial magnetic ground planes. In this thesis, several advances are added to the existing knowledge of developing artificial magnetic materials, in terms of analytical modeling, applications, realization, and experimental characterization. To realize AMMs with miniaturized unit cells, new inclusions based on fractal Hilbert curves are introduced, and analyzed. Analytical models, numerical full wave simulation, and experimental characterization are used to analyze, and study the new structures. A comprehensive comparison is made between the new inclusions, and perviously developed inclusions in terms of electromagnetic properties. The new inclusions have advantages of miniaturization, and less dispersion when compared to the existing structures in the literature. To realize multi-band AMMs, unit cells with multiple inclusions are proposed, designed, and analyzed. The new unit cells can be designed to give the desired magnetic properties either over distinguished multiple frequency bands, or over a single wide frequency band. Numerical full wave simulation is used to verify the proposed concept, and analytical models are provided for design, and optimization of the new unit cells. Unit cells with different configurations are optimized to get a wideband responce for the effective permeability. Space mapping technique is used to provide a link between analytically optimized structures, and full wave numerical simulation results. Two new methods are proposed for experimental characterization of artificial structures using microstrip, and strip line topologies. Using numerical results, the effect of anisotropy on the accuracy of the extracted parameters are investigated, and a fitting solution is proposed, and verified to address this challenge. New structures based on 2nd , and 3rd order fractal Hilbert curves are fabricated, and characterized using microstrip line, and strip line fixtures. Experimental results are presented, and compared with numerical results. The new experimental methods have advantages of lower cost, easier to fabricate and measure, and smaller sample size when compared to the existing methods in the literature. A new application is proposed for use of magnetic materials to develop wide band artificial magnetic conductors (AMC). Analytical models, and numerical analysis is used to validate the concept. A new ultra wideband AMC is designd, and analysed. The designed AMC is used as the ground plane to develop a low profile high gain ultra wide band antenna. The designed antenna is simulated, and its return loss, and gain is presented over a wide range of frequencies. A comprehensive study is presented on the performance of AMMs for the application of miniaturized antennas. A miniaturized antenna, using fractal Hilbert metamaterials as substrate, is fabricated, and measured. Measurement results are presented, and compared with numerical results. A parametric study is presented on the effect of the constitutive parameters of the artificial substrate on the performance of the miniaturized antenna. In this study, the effect of magnetic loss of AMM on the gain, and efficiency of the antenna, as well as the effect of dispersion of AMM on the bandwidth of the antenna is investigated.

Artificial Magnetic Materials (AMMs) are a subgroup of metamaterials which are engineered to provide desirable magnetic properties not seen in natural materials. These artificial structures are designed to provide either negative or enhanced positive (higher than one) relative permeability. AMMs with negative permeability are used to develop Single Negative (SNG), or Double Negative (DNG) metamaterials. AMMs with enhanced positive permeability are used to provide magneto-dielectric materials at microwave frequencies where the natural magnetic materials fail to work efficiently. AMMs are realized by embedding metallic resonators in a host dielectric. These inclusions provide desirable magnetic properties near their resonance frequency. Artificial magnetic materials used as SNG, or DNG have many applications such as: sub-wavelength cavity resonators, sub-wavelength parallel-plate wave guides, sub-wavelength cylindrical and spherical core–shell systems, efficient electrically small dipole antennas, super lenses, THz active devices, sensitivity enhancement near-field probes using double and single negative media, and mutual coupling reduction between antennas. On the other hand, artificial magnetic materials used as magneto-dielectrics have other applications in developing enhanced bandwidth efficient miniaturized antennas, low profile enhanced gain antennas using artificial magnetic superstrates, wide band woodpile Electromagnetic Band Gap (EBG) structures, EBGs with enhanced in-phase reflection bandwidth used as artificial magnetic ground planes. In this thesis, several advances are added to the existing knowledge of developing artificial magnetic materials, in terms of analytical modeling, applications, realization, and experimental characterization. To realize AMMs with miniaturized unit cells, new inclusions based on fractal Hilbert curves are introduced, and analyzed. Analytical models, numerical full wave simulation, and experimental characterization are used to analyze, and study the new structures. A comprehensive comparison is made between the new inclusions, and perviously developed inclusions in terms of electromagnetic properties. The new inclusions have advantages of miniaturization, and less dispersion when compared to the existing structures in the literature. To realize multi-band AMMs, unit cells with multiple inclusions are proposed, designed, and analyzed. The new unit cells can be designed to give the desired magnetic properties either over distinguished multiple frequency bands, or over a single wide frequency band. Numerical full wave simulation is used to verify the proposed concept, and analytical models are provided for design, and optimization of the new unit cells. Unit cells with different configurations are optimized to get a wideband responce for the effective permeability. Space mapping technique is used to provide a link between analytically optimized structures, and full wave numerical simulation results. Two new methods are proposed for experimental characterization of artificial structures using microstrip, and strip line topologies. Using numerical results, the effect of anisotropy on the accuracy of the extracted parameters are investigated, and a fitting solution is proposed, and verified to address this challenge. New structures based on 2nd , and 3rd order fractal Hilbert curves are fabricated, and characterized using microstrip line, and strip line fixtures. Experimental results are presented, and compared with numerical results. The new experimental methods have advantages of lower cost, easier to fabricate and measure, and smaller sample size when compared to the existing methods in the literature. A new application is proposed for use of magnetic materials to develop wide band artificial magnetic conductors (AMC). Analytical models, and numerical analysis is used to validate the concept. A new ultra wideband AMC is designd, and analysed. The designed AMC is used as the ground plane to develop a low profile high gain ultra wide band antenna. The designed antenna is simulated, and its return loss, and gain is presented over a wide range of frequencies. A comprehensive study is presented on the performance of AMMs for the application of miniaturized antennas. A miniaturized antenna, using fractal Hilbert metamaterials as substrate, is fabricated, and measured. Measurement results are presented, and compared with numerical results. A parametric study is presented on the effect of the constitutive parameters of the artificial substrate on the performance of the miniaturized antenna. In this study, the effect of magnetic loss of AMM on the gain, and efficiency of the antenna, as well as the effect of dispersion of AMM on the bandwidth of the antenna is investigated.

In this thesis, the commercial viability of the aminolytic synthesis method is explored through robustness, versatility, and waste reduction studies. We report the preparation of metal precursors and the development of a synthetic approach using an aminolytic reaction of metal carboxylates in oleylamine and non-coordinating solvent. Manganese doping in the cobalt ferrites allows for the investigation of the couplings. All the compositions in the series Co1-xMnxFe2O4, 0.0  x  1.0 were synthesized via the aminolytic reaction. The coercivity decreases with increasing Mn2+ concentration due to reducing of high magnetic anisotropy ion (Co2+) content. To our knowledge, this work is the first completed series of Co1-xMnxFe2O4. The method is used to synthesize manganese ferrites dope with chromium. This allows for the investigation of the effects of orbital momentum quantum coupling. All the compositions of MnFe2-xCrxO4, x= 0.0, 0.05, 0.13, 0.25, 0.43, 0.62, and 0.85, were synthesized via the In-situ aminolytic method. Chromium concentration weakens the couplings resulting in the decrease in overall magnetic moment. All by-products can be recycled for re-utilization. The "mother" solution can be used for multiple batches without treatment. Our trials have shown that the reaction could undergo ten reactions using the same solution without scarifying the quality or yield of the product. Finally, an environmental application is explored through the use of iron oxides. Samples of goethite, maghemite, magnetite, and hematite were synthesized and characterized. These nanoparticles were exposed to arsenic and chromium solutions to measure the percent uptake of contaminant by each phase. Adsorption isotherms were plotted to obtain Freundlich parameters. The adsorption constant (K) averages over a 400% increase on literature values. We synthesized hematite and maghemite core-shell particles and exposed them to arsenite and maghemite core-shell particles have the higher removal affinity due to their smaller size.

This thesis documents the work and research effort on the design, fabrication and testing of a magnetocaloric MEMS microcooler, focusing on the testing of the microcooler at low magnetic fields. The phenomenon of magnetocaloric effect (MCE), or adiabatic temperature change, which is obtained by heating or cooling magnetic materials due to a varying magnetic field, can be exploited in the area of magnetic refrigeration as a reliable, energy-efficient cooling system. In particular, its applications are being explored primarily in cryogenic technologies as a viable process for the liquefaction of hydrogen. The challenge for magnetic refrigeration is that the necessary MCE is most easily achieved with high magnetic fields (5-6 Tesla) provided by superconducting magnets. However, a significant magnetocaloric effect can be exhibited at lower magnetic fields (1-2 Tesla) by carefully controlling initial temperature conditions as well as by selecting, preparing and synthesizing the optimal fabrication process of Silicon (Si) wafers. A microcooler was integrated based on previous works of others and tested. Finally, testing of the magnetocaloric effect was conducted and results analyzed. Experimental results in these domains demonstrate that magnetic refrigeration can be part of the best current cooling technology, without having to use volatile, environmentally hazardous fluids. The MEMS magnetocaloric refrigerator demonstrated a ~ -12°C change in the temperature of cooling fluid at a magnetic field of 1.2 T.

The study of magnetic properties and structures of Zn and Cd substituted mixed ferrites has been carried out using Mossbauer spectroscopy and X-ray diffraction on powdered samples at about 300 K. Two series of mixed ferrites, (Cd, Zn)xCol-xFe2-xAlxO4 and (Cd, Zn)xCo0.9Fe1.7-xTi0.4O 4 (where 0≤ x≤1.0) were synthesized. In the former series the effect of simultaneous site dilution by Zn or Cd and Ai atoms on tetrahedral (A) and octahedral (B) sites is investigated and in the latter the effect of single site dilution by Zn or Cd is also studied. The Mossbauer spectra show that the compounds transform with increase in x from ordered to disordered magnetic states. Systematic decrease in the hyperfine fields indicating weakening of the magnetic coupling with an increase in x is observed. We report the presence of a cross over effect with respect to the hyperfine fields on A and B sites at low concentration of diamagnetic ions in the simultaneously diluted series. Both series of compounds show no significant changes in isomer shifts with x. Differences in the evolution of Fe atoms on A and B sites between Zn and Cd based compounds are observed. The results of our analysis show that Zn and Cd ions occupy both tetrahedral and octahedral sites. The spinel structure of the compounds studied in this work is confirmed by X-ray diffraction (XRD). The lattice parameters derived from XRD show systematic change with x consistent with Vergard's law. In Cd based samples an increase of the lattice parameter with x is explained on the basis of the size difference of the cations involved. However, an anomalous behavior of the lattice parameter is observed in Zn based samples. The average grain sizes of the samples were determined from the line width of the (311) XRD intensity lines using the Scherrer formula. These vary between 50 nm and 70 nm for all the samples except for Zn and Al substituted samples which show a systematic anomalous reduction for x ≥ 0.4 in grain size. The porosity, x-ray and bulk densities of the samples are also presented. / Thesis (M.Sc.)-University of Natal, Durban, 2002.

No description available.

Metal oxide nanoparticles, both magnetic and nonmagnetic, have a multitude of applications in gas sensors, catalysts and catalyst supports, airborne trapping agents, biomedicines and drug delivery systems, fuel cells, laser diodes, and magnetic microwaves. Over the past decade, an inexpensive, simple, recyclable, and environmentally friendly large, scale synthesis method for the synthesis of these metal oxide nanoparticles has been sought. Many of the current techniques in use today, while good on the small, laboratory bench scale, suffer from drawbacks that make them unsuitable for the industrial scale. The aminolytic method, developed by Dr. Man Han while working for Dr. Zhang, fits industrial scale-up requirements. The aminolytic method involves a reaction between metal carboxylate(s) and oleylamine in a non-coordinating solvent. This system was shown to produce a range of spinel ferrites. Dr. Lisa Vaughan showed that this method can be recycled multiple times without degrading the quality of the produced nanoparticles. The purpose of this thesis is to test the versatility of the aminolytic method in the production of a wide range of metal oxides as well as various core/shell systems. Chapter 2 explores the effect of precursor carboxylates chain length on the aminolytic synthesis of cobalt ferrite, and manganese ferrite nanoparticles. In Chapter 3, a series of CuxMn1-xFe₂O₄, (x ranges from 0.0 to 0.2), nanoparticles were synthesized via the aminolytic method. This series allows for the investigation of the effects of orbital Jahn-Teller distortion as well as orbital angular momentum on the magnetic properties of this ferrite. The quantum couplings of magnetic ions in spinel ferrites govern their magnetic properties and responses. An understanding of the couplings between these metal ions allows for tailoring magnetic properties to obtain the desired response needed for various applications. Chapter 4 investigates the synthesis of MnO and Mn₃O₄ nanoparticles in pure single phase with high monodispersity. To the best of our knowledge, the range of sizes produced for MnO and Mn₃O₄ is the most extensive, and therefore a magnetic study of these systems shows some intriguing size dependent properties. The final part of this chapter investigates the applicability of the aminolytic method for building a MnO shell on a CoFe₂O₄ core. Chapter 5 explores the synthesis of another metal oxide, ZrO₂ in both the cubic and monoclinic phases with no impurities. The use of the aminolytic method here removes the need for dangerous/expensive precursors or equipment and eliminates the need for extensive high temperature heat treatments that destroy monodispersity which is required for most techniques. The creation of a core/shell system between CoFe₂O₄ and ZrO₂ using the aminolytic method was also tested. This core/shell system adds magnetic manipulation which is especially useful for the recovery of zirconia based photocatalyst. Chapter 6 studies the application of the aminolytic method in the synthesis of yttrium iron garnet (YIG) and yttrium iron perovskite (YIP) nanoparticles. Current synthesis techniques used to produce YIG and YIP nanoparticles often requires high temperatures, sensitive to contamination, which could be eliminated through the use of our method

The syntheses, structures, and magnetic properties of a series of di/trivalent hydridotris(3,5-dimethylpyrazol-1-yl)borate (Tp*) cyanomanganates were investigated. Treatment of manganese(III)acetylacetonate with KTp* followed by tetra(ethyl)- ammonium cyanide affords [NEt4][(Tp*)MnII(acac)(CN)] (1). Attempts to oxidize 1 with iodine affords {(Tp*)MnII(κ2O-acac-CN)}n (7); a minor complex {[NEt4][(Tp*)MnII(κ2O-acac-3-CN)]2(µ-CN) (8) was also isolated. The manganese(II) complex [NEt4][(Tp*)MnII(κ2O-acac-3-CN)(κ1N -3-NC-acac)] (2) was obtained via treatment of Mn(3-acacCN)3 with KTp* and [NEt4]CN. [NEt4]2[MnII(CN)4] (3) was prepared via treatment of Mn(OTf)2 with excess [NEt4]CN. [NEt4][(Tp*)MnIII(CN)3] (4), is prepared via treatment of 4 with Mn(3-acacCN)3, KTp* and excess [NEt4]CN. [PPN][(Tp*)MnIII(CN)3] (5) is obtained via treatment of [PPN]3[MnII(CN)6] with (Tp*)SnBu2Cl. Combination of 4 with [MnII(bipy)2(OH2)2][OTf]2 afforded a tetranuclear rectangular cluster {MnIII 2MnII 2} (9). At low temperature, {MnIII2NiII2} (10) was prepared via treatment of 4 and [Ni(II)(bipy)2(H2O)2][OTf]2. Treatment of 4 with [CoII(bipy)2(OH2)2][OTf]2 at low temperature failed to give the desired {MnIII2CoII2} complex. Magnetic measurements indicate that 1, 2, and 7 contain high-spin isotropic MnII with no long-range magnetic order observed for 7 (T > 2 K); 4 contains low-spin MnIII that likely adopt an isotropic 3A2 spin ground state. Surprisingly 9 and 10 do not exhibit slow relaxation of the magnetization (for T > 1.8 K) despite the presence of significant molecular anisotropy.

This work includes formulation of mechanically flexible magnetic composites and application to a quarter-wavelength microstrip patch antenna benchmarking structure operating in the lower UHF spectrum (~300-500 MHz) to investigate capability for miniaturization. A key challenge is to introduce sufficiently low magnetic loss for successful application. Particles of NiZn ferrite and BaCo ferrite, also known as Co2Z, were characterized. Flexible magnetic composites comprised of 40 vol% NiZn ferrite or BaCo ferrite particles in a silicone matrix were formulated. Effects of treating the particles with silane in the formulation process were not detectable, but larger particle size showed to increase complex permittivity and complex permeability. By comparing complex permittivity and complex permeability of the composites, BaCo ferrite was selected for the antenna application. Antennas on the developed magnetic composite and pure silicone substrates were electromagnetically modeled in a full-wave FEM EM solver. A prototype of the antenna on the magnetic composite was fabricated. Good agreement between the simulated and measured results was found. Comparison of the antennas on the magnetic composite versus the pure silicone substrate showed miniaturization capability of 2.4X and performance differences of increased bandwidth, reduced Q, and reduced gain. A key finding of this study is that a small amount of permeability (relative permeability ~2.5) can provide relatively substantial capability for miniaturization, while sufficiently low magnetic loss can be introduced for successful application at the targeted operating frequency. The magnetic composite showed the capability to fulfill this balance and to be a feasible option for RFID applications in the lower UHF spectrum.

Thesis (Ph. D.)--McMaster University (Canada), 1990. / Source: Dissertation Abstracts International, Volume: 52-10, Section: B, page: 5290. Supervisor: M.F. Collins.