chemical partitioning of Cobalt-containing soft magnetic amorphous and nanocomposite materials has been investigated with particular focus on its consequences on these materials’ nanostructure and electrical resistivity. Theory, models, experiment, and discussion in this regard are presented on this class of materials generally, and are detailed in particular on alloys of composition, (Fe65Co35)79.5+xB13Si2Nb4-xCu1.5, for X={0- 4at%}, and Co-based, Co76+YFe4Mn4-YB14Si2Nb4, for Y={0-4at%}. The context of this work is within the ongoing efforts to integrate soft magnetic metal amorphous and nanocomposite materials into electric motor applications by leveraging material properties with motor topology in order to increase the electrical efficiency and decrease the size, the usage of rare-earth permanent magnets, and the power losses of electric motors. A mass balance model derived from consideration of the partitioning of glass forming elements relates local composition to crystal state in these alloys. The ‘polymorphic burst’ onset mechanism and a Time-Temperature- Transformation diagram for secondary crystallization are also presented in relation to the partitioning of glass forming elements. Further, the intrinsic electrical resistivity of the material is related to the formation of virtual bound states due to dilute amounts of the glass forming elements. And lastly, a multiphase resistivity model for the effective composite resistivity that accounts for the amorphous, crystalline, and glass former-rich amorphous regions, each with distinct intrinsic resistivity, is also presented. The presented models are validated experimentally on the Co-containing alloys by Atom Probe Tomography performed through collaboration with Pacific Northwestern National Laboratory.

Targeted therapy is a significant area of research in pharmaceutical and biomedical science. Its overall aim is to achieve maximum impact on malignant cells with minimum side effects to healthy tissue. In this thesis the capabilities of magnetic microbubbles as targeted therapeutic delivery vehicles are explored. New characterisation techniques were developed in order to understand and improve the current magnetic microbubble formulation. Electron microscopy was used to analyse the nanoscale structure of microbubble shells and observe nanoparticles attached to the shell surface. A new flow phantom was developed and the targeting of magnetic microbubbles against flow conditions corresponding to those in the human body was found to be feasible in numerous vessel sizes and flow conditions. Magnetic targeting of microbubbles was also observed in a perfused porcine liver model. Magnetic targeting was then attempted against flowing blood and a decrease in targeting efficiency observed. This was also seen for biochemical targeting and collisions with red blood cells identified as the most likely cause. Importantly, the number of magnetically targeted microbubbles significantly exceeded those targeted via biochemical interactions in both blood and water. In the second part of the thesis new types of magnetic microbubble were developed. The first exploits the fusion of nano-scale magnetic droplets with phospholipid microbubbles. In the second magnetic nanoparticles were incorporated directly into the lipid shell. The new magnetic microbubble formulation could be magnetically targeted, observed via contrast ultrasound and was successfully used to deliver siRNA to neuroblastoma cells.

No description available.

Permanent magnets are used heavily for multiple applications in industry and current electronic technologies. However, the current permanent landscape is muddled by high cost of materials and insufficient magnetic or thermal properties. The primary focus of this dissertation work is the synthesis and optimization of a new permanent magnetic material, in the form of cobalt carbide nanomaterials. The optimization revolved around controlling the crystal phase and particle shape of synthesized cobalt carbide particles; these parameters have significant impact on the observed magnetic properties of magnetic nanoparticles. Co3C was identified to be the preferred crystal phase, leading to better magnetic properties. Cobalt Fumarate was found to be the ideal precursor to synthesize anisotropic Co3C particles and enhance magnetic properties of the synthesized cobalt carbide particles. Lastly, an ethanol based reduction system was employed to develop the greener synthesis of Co and Ni magnetic particles.

Magnetism lies at the core of modern technology and can be found in industries such as oil refining, automotive, telecommunications, personal electronics, and power generation that are integral to our day to day lives. This permeation into everyday life has been enhanced in the past several decades with improvements in material design based upon the principles of nanotechnology leading to smaller, faster, and more efficient devices. The presented research will discuss the synthesis and processing of multiple magnetic nanoparticle structures designed for the enhancement of various, application specific, properties. In the first experiments a tunable core/shell structure was developed with either enhanced optical properties or enhanced catalytic reactivity based solely upon small manipulations in the synthesis resulting in alternate morphologies. Essentially reaction times were controlled to direct core nucleation followed by shell growth and based upon addition times and concentration the final product could be manipulated as either a Fe/Ag or Ag/Fe core/shell. The modifications also resulted in Fe particles decorated with Ag islands that showed significant Plasmon shifts while still maintaining their high magnetization. These particles present applications in catalysts, sensors, and separations. Secondly FexCo100-x alloys were generated in order to determine the atomic compositions with the best magnetic properties. Several post-processing cleaning and annealing regimes were used to determine the most effective method of preparing the particles for utilization in devices. Annealing temperatures of 450°C were found most effective at enhancing magnetic properties while minimizing grain growth. Finally the synthesis of exchange-coupled hard magnetic core/shell nanoparticles was conducted. In this synthesis SmCo5 was synthesized via solvent assisted ball milling in oleic acid. Once completed these particles were processed in a multistep cleaning process which removed excess solvent and much of the surface oxidation. The particles were then suspended in a non-aqueous solvent and a magnetically coupled Co shell was carefully grown under sub-zero conditions. The resulting composite material demonstrated greatly enhanced magnetic properties and a unique laminated structure that had been elusive in nanoparticle research. Several magnetic nanoparticles and compositions were studied resulting in increased functionality based upon the bottom-up nanostructuring of materials. This work allows for the understanding of the effect of synthetic conditions on the control of nucleation and growth dynamics within nanoparticle synthesis and the generation of high quality functional magnetic materials.

We have studied magnetic properties of the intermetallic NdPd5Al2 com- pound by means of specific heat and magnetization measurements and neutron scattering. The compound crystallizes in the tetragonal I4/mmm space group with lattice parameters a =4.147 ˚A and c =14.865 ˚A, orders antiferromagnet- ically below TN =1.3 K and presents large magnetocrystalline anisotropy due to the crystal-field effects. The obtained magnetic phase diagram is charac- terized by two distinct magnetically ordered phases similarly to structurally re- lated tetragonal RTX5 and R2TX8 compounds. The zero-field antiferromagnetic phase is characterized by the propagation vector k = (1 2 00) and antiferromag- netic coupling of Nd moments along the teragonal c-axis with the amplitude of magnetic moments of 2.22 µB/Nd as was revealed by neutron diffraction. The transition from the paramagnetic to magnetically ordered in zero field is the first-order phase transition. The CF excitations in NdPd5Al2 were detected by means of INS at 3.0 meV, 7.4 meV, 8.6 meV and 17.1 meV. We further compare our findings about CF in NdPd5Al2 obtained from INS, susceptibility analysis and first-principles calculations and confront them with the experimental mag- netization and magnetic specific heat data. Our results will be also discussed with respect to related...

The purpose of this study is to inform instruction by increasing the body of knowledge regarding the relationship between college physics students' knowledge about models in science and their conceptual understanding with regard to electricity and magnetism. The data for this study was obtained through the administration of two instruments: Conceptual Survey of Electricity and Magnetism, a multiple choice assessment, and Student Understanding of Models in Science, a Likert-scale survey. Both traditional statistics and an innovative technique called Model Analysis were used to analyze the data. Analysis of the data revealed that there is a relationship between student understanding of models in science and conceptual understanding of electricity and magnetism topics. However, the results of this study also suggest that without specific instruction on models in science, overall understanding of models in science does not improve after a traditional electricity and magnetism course. Additionally, this study demonstrated that not only does student conceptual understanding of electricity and magnetism topics improve after a traditionally taught electricity and magnetism course, but also, students demonstrate more sophistication in their understanding of some electricity and magnetism topics. In the latter case, students showed improvement in their application of the expert rather than the naïve or null model of electricity and magnetism topics.

La découverte récente de supraconductivité à relativement haute température (Tc,max=56K) dans les pnictures de Fer soulève des questions fondamentales sur l’origine et la nature de la supraconductivité : en particulier, la présence d’une phase antiferromagnétique à proximité de celle-ci dans leur diagramme de phase, comme dans d’autres supraconducteurs non conventionnels pose la question du lien entre magnétisme et supraconductivité.Nous nous sommes intéressés à la nature de l’état normal ainsi que des phases antiferromagnétique et supraconductrice d’un point de vue local grâce à la Résonance Magnétique Nucléaire (RMN) dans les pnictures de Fer. Nous avons pour cela étudié des pnictures de Fer de même composé parent BaFe2As2 pour des substitutions Co en site Fer de nature hétérovalente et réalisant un dopage électron ou bien Ru en site Fer de nature isovalente. L’état normal de ces matériaux présente des différences notables avec l’état normal des cuprates supraconducteurs : le désordre introduit par les substitutions au niveau intraplan est faible et on constate l’absence d’une phase de PseudoGap pour la susceptibilité de spin. Les diagrammes de phase sont similaires pour le Co et le Ru mais nos mesures montrent que la nature des phases antiferromagnétique et supraconductrice est en réalité qualitativement différente à l’échelle locale pour les deux types de substitution. Pour la substitution au Co réalisant un dopage électron, les phases électroniques sont homogènes et nous démontrons en particulier qu’à certains dopages, un ordre antiferromagnétique incommensurable coexiste avec la supraconductivité jusqu’à une échelle atomique, suggérant une nature itinérante du magnétisme et un état supraconducteur possédant une symétrie non conventionnelle. Pour la substitution isovalente au Ru, les phases électroniques sont inhomogènes à une échelle étonnamment faible, de l’ordre du nanomètre, mettant en jeu une coexistence entre magnétisme et supraconductivité très distribuée spatialement. Ce travail illustre la possibilité d’engendrer une phase supraconductrice non conventionnelle en déstabilisant une phase antiferromagnétique au moyen de mécanismes agissant soit dans l’espace réciproque (dopage électron), soit dans l’espace réel (substitution isovalente) et donnant lieu par ailleurs à une coexistence de ces phases de nature très différente dans les deux cas. / The recent discovery of superconductivity at a rather high temperature in the iron pnictides (Tc,max=56K) has revived some fundamental questions about the existence and the nature of the superconducting phase : in particular, the existence of an antiferromagnetic phase that is in vicinity of the superconducting phase in their phase diagram, as in other unconventional superconductors, raises questions about the link between magnetism and superconductivity. In this thesis, we studied the normal state as well as the antiferromagnetic and superconducting phases of the iron pnictides on a local scale with Nuclear Magnetic Resonance (NMR). Starting from the same parent compound BaFe2As2, we studied heterovalent Co substitution in Fe site realizing an electron doping and isovalent Ru substitution in Fe site. The normal state is shown to display important qualitative differences with the normal state of cuprates superconductors: disorder induced substitutions in electronically active layers is weak and we show the absence of a PseudoGap phase from spin susceptibility measurements. Whereas the phase diagram is similar for Co and Ru substitutions, we show that the nature of the antiferromagnetic and the superconducting phases is qualitatively different on a local scale in the two cases. For Co substitution leading to electron doping, the electronic phases are homogeneous and we demonstrate in particular the homogeneous coexistence of antiferromagnetism and superconductivity down to an atomic scale for some compositions: this suggests a magnetism of itinerant nature and an unconventional superconducting order parameter for the superconducting phase. For the isovalent Ru substitution, the electronic phases are inhomogeneous at a scale surprisingly low of the order of the nanometer scale, leading to a coexistence that is very distributed spatially. This works shows the possibility to induce an unconventional superconducting phase by the weakening of an antiferromagnetic phase made possible with very different means : either in reciprocal space with electron doping or in real space with isovalent substitution. Moreover, this is shown to lead to different kinds of coexistence between these phases in the two cases.

With the increasing demand for high storage density, magnetic recording media will soon have as their basic components single-domain ferromagnetic grains. Recently experimentalists working with powerful new microscopic techniques have discovered that the process of magnetization reversal in these grains is much more complicated than had been previously realized. In this dissertation we investigate the applicability of the two-dimensional kinetic Ising model on a square lattice as a model for the switching dynamics. The process of metastable decay is studied by two means: Monte Carlo simulations and analytical arguments based on droplet theory. The simulations are shown to be consistent with the analytical arguments and qualitatively similar to the experimental measurements of single-domain ferromagnets. / For a periodic Ising system with an initial magnetization $m\sb0$ = +1 in a negative magnetic field, the field $H\sb{\rm sw}$ which causes the magnetization to decay to zero in a specified length of time is found as a function of the system size L. The probability that the magnetization remains greater than zero is also found as a function of time for fixed applied field and as a function of applied field for fixed decay time. / The magnetostatic dipole-dipole interaction in real magnetic materials is modeled to lowest order by adding to the Ising Hamiltonian a term proportional to the square of the magnetization. The analytical predictions show excellent agreement with Monte Carlo simulations with no fitted parameters that depend on the $m\sp2$ term. / Finally, $H\sb{\rm sw}$ is found from Monte Carlo simulations of octagonal systems with a variety of boundary conditions. The results are explained in terms of the scaling form of the free-energy barrier which must be overcome for the metastable state to decay, and they demonstrate the importance that surface effects such as adsorption and reconstruction might have on magnetization switching. / Source: Dissertation Abstracts International, Volume: 57-04, Section: B, page: 2634. / Major Professor: Per Arne Rikvold. / Thesis (Ph.D.)--The Florida State University, 1996.

Magnetismo ambiental é uma área nova e multidisciplinar que estuda propriedades magnéticas de solos, sedimentos, rochas e relaciona essas propriedades com parâmetros ambientais e poluição. Assim a caracterização dos minerais presentes em solos e sedimentos é ferramenta fundamental de estudo, principalmente devido à presença do Fe. Com este objetivo, amostras de sedimentos foram coletadas na forma de testemunhos no Largo de Santa Rita (LSR) e Rio Casqueiro (CS2), Santos, São Paulo (no presente trabalho acrescentamos aos cálculos também a contribuição dos óxidos de ferro) e Ferraz (FZ) e Botany Point (BP), da baia do Almirantado, Ilha Rei George, Antártica Os testemunhos da baia de Santos são semelhantes porque são provenientes de uma região extremamente poluída. De outra forma, os testemunhos da Antártica são semelhantes por serem de regiões sem ocupação humana. Assim um interesse específico em estudar amostras destas regiões é justificado. E amostras isoladas de superfície da plataforma continental do Rio de Janeiro e São Paulo, incluindo amostras da ilha do Cardozo e ilha Anchieta, por apresentarem particularidades interessantes. As amostras foram caracterizadas por Espectroscopia Mössbauer (EM), Susceptibilidade Magnética (SM) e PIXE (Particle Induced X-ray Emission). Esta última técnica permite detectar e quantificar elementos químicos de número atômico acima de 12. Os elementos quantificados nos resultados de PIXE são: em todas as amostras Al, Si, S, Cl, K, Ti, Mn e Fe; no testemunho LSR: P, V, Co ; no testemunho CS2: P, V, Cr, Co, Ni, Cu, Zn, As, Br e Zr; no testemunho BP: V, Cr, Co, Cu, Zn, I e W; no testemunho FZ: V, Cr, Co, Ni, Cu, Zn e I; na amostra PEN: P, Co; na amostra CARD: P e Mo; na amostra P6947: Cr, Co, Ni, Cu, Zn, Br e I; na amostra P6949: Cr, Co, Cu, Zn e La; na amostra P6561: Cr, Co, Ni, Br e I; na amostra P6626: Co, Ni, Cu, Zn, I, Sr e Zr e na amostra P6627: Cr, Co, Ni, Cu, Zn, Br, I e Sr. A partir das medidas de EM determinamos as proporções de Fe2+, Fe3+ paramagnético e de Fe3+ ligado aos óxidos de ferro e os identificamos. Determinamos que o óxido de ferro presente nos testemunhos LSR e CS2 é a goethita. O óxido de ferro identificado nas amostras dos testemunhos Ferraz e Botany Point foi a hematita. Esta também foi identificada na amostra da praia do engenho, ilha Anchieta. Em única amostra entre as amostras da plataforma continental foi detectado e quantificado um óxido de ferro. Nas amostras dos testemunhos do litoral de São Paulo, a fase do ferro predominante é a paramagnética, portanto, associamos a fase paramagnética do ferro ao predomínio do intemperismo químico. Por outro lado amostras dos testemunhos da Antártica, a fase do ferro predominante é dos óxidos de ferro, portanto, associamos a fase de óxidos de ferro ao predomínio de intemperismo físico. Assim a presença de ferro amorfo (ferridrita ou fugerita) poderia ser um índice de quantidade de metais de transição presentes na coluna sedimentar. Modelamos o valor da susceptibilidade magnética ponderando as contribuições individuais de cada elemento químico e do Fe3+, do Fe2+ e dos óxidos de ferro. O cálculo da susceptibilidade magnética modelada é a contribuição original deste trabalho, onde verificamos que os picos no valor de Susceptibilidade Magnética correspondem às situações de maior contaminação ambiental. Por fim, concluímos que nossos resultados de Espectroscopia Mössbauer, PIXE e Susceptibilidade Magnética estão de acordo e podem ser usados em modelos com o objetivo de observar impactos ambientais. / Environmental magnetism is a new area that studies magnetic properties of soils, sediments and rocks and relates these properties with environmental parameters and pollution. With this proposal sets of sediments were collected from the Largo Santa Rita(LSR), Santos, São Paulo; from Baia do Almirantado, Rei George, Antarctic, Ferraz (FZ) and Botany Point (BP); Rio Casqueiro, Cubatão, São Paulo (CS2, re-studied in the present work including oxides contribution) and isolated samples of Plataforma Continental. The CS2 and LSR samples are similar from a heavily polluted region. On the other hand, FZ and BP samples are similar from regions without human occupation. Thus a specific interest to study samples from these regions is justified. The samples were characterized by Mössbauer Spectroscopy (MS), Magnetic Susceptibility and PIXE (Particle Induced X-ray Emission). The latter allowed to detect and to quantify the content of chemical elements of atomic number above 12. The presence of trace metals as Al, Si, S, Cl, K, Ti, Mn and Fe was detected and quantified using the PIXE technique in all samples. P, V, Co were detected and quantified in LSR samples. P, V, Cr, Co, Ni, Cu, Zn, As, Br and Zr were detected and quantified in CS2 samples. V, Cr, Co, Cu, Zn, I and W were detected and quantified in BP samples. V, Cr, Co, Ni, Cu, Zn and I were detected and quantified in FZ sample. P and Co were detected and quantified in PEN sample. P and Mo were detected and quantified in CARD sample. Cr, Co, Ni, Cu, Zn, Br and I were detected and quantified in P6947 sample. Cr, Co, Cu, Zn and La were detected and quantified in P6949 sample. Cr, Co, Cu, Zn and La were detected and quantified in P6561 sample. Co, Ni, Cu, Zn, I, Sr, Zr and La were detected and quantified in P6626 sample. Cr, Co, Ni, Cu, Zn, Br, I e Sr were detected and quantified in P6627 sample. The Mössbauer measurements presents Fe2+ and Fe3+ sites and in some samples an additional sextet, due the presence of goethite for LSR and CS2 samples, hematite for FZ and BP samples. The relative area of paramagnetic iron was larger than the others MS components in samples of São Paulo, Litoral, so we associated chemistry weathering with paramagnetic phases. On the other hand, the iron oxides relative áreas of Antarctic samples were larger than the others MS components, so we associated physical weathering with magnetic iron oxides phases. Thus the paramagnetic iron detected could be a measure of transition metals presence or a pollution index. The peaks of experimental magnetic susceptibility curve were related to pollution. The combined results of MS and PIXE allowed us to perform the fitting of the magnetic susceptibility curve that yield a perfect fit with experimental data. In the particular case of Fe we used the related proportions of Fe2+ and Fe3+ obtained by MS measurements. The iron oxides contributions are also found in literature. The model of magnetic susceptibility is the original contributed of the present work. We can conclude that our results of MS, PIXE and magnetic susceptibility are in good agreement and can be used in models with the objective to study the environmental impacts effects.