In this presentation it is demonstrated that the unique magnetic properties of superparamagnetic cobalt-spinel ferrite nanoparticles can be employed in several novel applications. A method to selectively capture and remove pathogens from infected organisms to improve longevity is presented. Evidence is provided to show that automated methods using modified forms of hemofiltration or peritoneal dialysis could be used to eliminate the particle/pathogen or particle/infected cell conjugates from the organism postoperatively. It is shown that disparately functionalized nanoparticles can be used in concert as drug carrier and release mechanisms. Lastly, we provide preliminary evidence to support the use of magnetic nanoparticles for controlling reaction kinetics.

No description available.

A matrix of variably processed Fe-30at%Ni was deposited with variations in laser travel speeds as well and laser powers. A complete shift in phase stability occurred as a function of varying laser travel speed. At slow travel speeds, the microstructure was dominated by a columnar fcc phase. Intermediate travel speeds yielded a mixed microstructure comprised of both the columnar fcc and a martensite-like bcc phase. At the fastest travel speed, the microstructure was dominated by the bcc phase. This shift in phase stability subsequently affected the magnetic properties, specifically saturation magnetization. Ni-Fe-Mo and Ni-Fe-V permalloys were deposited from an elemental blend of powders as well. Both systems exhibited featureless microstructures dominated by an fcc phase. Magnetic measurements yielded saturation magnetizations on par with conventionally processed permalloys, however coercivities were significantly larger; this difference is attributed to microstructural defects that occur during the additive manufacturing process.

No description available.

No description available.

No description available.

No description available.

No description available.

Electron-lattice interactions are often considered not to play a major role in material's properties as they are assumed to be small, the second-order effects. However, this study shows the importance of taking these effects into account in the simulations. My results demonstrate the impact of the electron-lattice interaction on the physics of the material and our understanding from it. One way to study these effects is to add them as perturbations to the unperturbed Hamiltonians in numerical simulations. The main objective of this thesis is to study electron-lattice interactions in molecular and magnetic crystals. It is devoted to developing numerical techniques considering model Hamiltonians and first-principles calculations to include the effect of lattice vibrations in the simulations of the above mentioned classes of materials. In particular, I study the effect of adding the non-local electron-phonon coupling on top of the Holstein Hamiltonian to study the polaron stability and polaron dynamics in molecular crystals. The numerical calculations are based on the semi-empirical Holstein-Peierls model in which both intra (Holstein) and inter (Peierls) molecular electron-phonon interactions are taken into account. I study the effect of different parameters including intra and intermolecular electron-phonon coupling strengths and their vibrational frequencies, the transfer integral and the electric field on polaron stability. I found that in an ordered two dimensional molecular lattice the polaron is stable for only a limited range of parameter sets with the polaron formation energies lying in the range between 50 to 100 meV. Using the stable polaron solutions, I applied an electric field to the system and I observed that the polaron is dynamically stable and mobile for only a limited set of parameters. Adding disorder to the system will result in even more restricted parameter set space for which the polaron is stable and moves adiabatically with a constant velocity. In order to study the effect of temperature on polaron dynamics, I include a random force in Newtonian equations of motion in a one dimensional molecular lattice. I found that there is a critical temperature above which the polaron destabilizes and becomes delocalized. Moreover, I study the role of lattice vibrations coupled to magnetic degrees of freedom in finite temperature paramagnetic state of magnetic materials. Calculating the properties of paramagnetic materials at elevated temperatures is a cumbersome task. In this thesis, I present a new method which allows us to couple lattice vibrations and magnetic disorder above the magnetic transition temperature and treat them on the same footing. The method is based on the combination of disordered local moments model and ab initio molecular dynamics (DLM-MD). I employ the method to study different physical properties of some model systems such as CrN and NiO in which the interaction between the magnetic and lattice degrees of freedom is very strong making them very good candidates for such a study. I calculate the formation energies and study the effect of nitrogen defects on the electronic structure of paramagnetic CrN at high temperatures. Using this method I also study the temperature dependent elastic properties of paramagnetic CrN. The results highlight the importance of taking into account the magnetic excitations and lattice vibrations in the studies of magnetic materials at finite temperatures. A combination of DLM-MD with another numerical technique namely temperature dependent effective potential (TDEP) method is used to study the vibrational free energy and phase stability of CrN. We found that the combination of magnetic and vibrational contributions to the free energy shifts down the phase boundary between the cubic paramagnetic and orthorhombic antiferromagnetic phases of CrN towards the experimental value. I used the stress-strain relation to study the temperature-dependent elastic properties of paramagnetic materials within DLM-MD with CrN as my model system. The results from a combinimation of DLM-MD with another newly developed method, symmetry imposed force constants (SIFC) in conjunction with TDEP is also presented as comparison to DLM-MD results.I also apply DLM-MD method to study the electronic structure of NiO in its paramagnetic state at finite temperatures. I found that lattice vibrations have a prominent impact on the electronic structure of paramagnetic NiO at high temperatures and should be included for the proper description of the density of states. In summary, I believe that the proposed techniques give reliable results and allow us to include the effects from electron-lattice interaction in simulations of materials.

As ligas de FeRh apresentam um comportamento não usual quando encontradas próximas da composição equiatômica, sendo observada uma transição de fase magnetoestrutural de primeira ordem, na qual o sistema passa de um estado antiferromagnético para um estado ferromagnético com a temperatura crítica próxima da temperatura ambiente. A temperatura crítica de transição é fortemente dependente da composição da liga, das técnicas de produção e dimensionalidade da amostra, além de fatores externos como pressão e campo magnético. No presente trabalho foram depositados, via magnetron sputtering, filmes de FeRh (monocamadas) e FeRh/Fe (bicamadas) sobre substratos monocristalinos de MgO (001), sendo utilizado duas temperaturas de deposição diferentes: 798 K e 913 K. A estrutura cristalina dos filmes foi analisada através de técnicas de medidas de difração de raios X (varredura &theta - 2 &theta, varredura em &phi e rocking curves) e as composições e espessuras dos filmes foram analisadas por medidas de RBS. A principal diferença morfológica encontrada entre as amostras foi uma melhor uniformidade na distribuição de orientações dos grãos cristalinos nos filmes depositados na temperatura mais elevada. As propriedades magnéticas, medidas por meio de um VSM equipado com um criostato e um forno, evidenciaram diferenças entre as amostras depositadas nas diferentes temperaturas mencionadas, observando-se variações significativas nas temperaturas de transição de fase e diferentes larguras dos ciclos térmicos. Também foi observado, em todas as amostras, coexistência de fases antiferromagnética e ferromagnética na camada de FeRh, principalmente na região de baixas temperaturas. As amostras depositadas em 798 K foram mais favoráveis à formação da fase FeRh antiferromagnética e, no caso das bicamadas, também apresentaram um melhor acoplamento entre as camadas de FeRh e Fe que as amostras depositadas em 913 K, favorecendo um incremento do campo coercivo e da magnetização remanente relativa do sistema. / FeRh alloys, near the equiatomic composition, present an unusual magneto structural first-order phase transition in which the system changes from antiferromagnetic to ferromagnetic state at a critical temperature close to ambient temperature. The critical transition temperature is strongly dependent on the alloy composition, production techniques and dimensionality of the sample, as well as external factors such as pressure and magnetic field. In the present work, FeRh (monolayers) and FeRh/Fe (bilayers) films were deposited on monocrystalline MgO (001) substrates, via magnetron sputtering, at two different deposition temperatures: 798 K and 913 K. The crystalline structures of the films were analyzed by using different techniques of X-ray diffraction (&theta - 2 &theta scan, &phi scan and rocking curves). The compositions and thicknesses of the films were analyzed by RBS measurements. The main morphological difference between the samples was a better uniformity in the distribution of crystalline grain orientations in the films deposited at higher temperature. The magnetic properties, which were measured by a VSM equipped with a cryostat and an oven, revealed differences between the samples obtained at different temperatures. Significant variations in the critical phase transition temperatures and different widths of thermal cycles were observed. It was also observed, in all samples, coexistence of antiferromagnetic and ferromagnetic phases in the FeRh layer, mainly at low temperatures. The samples deposited at 798 K were more favorable to the formation of the antiferromagnetic FeRh phase. In addition, for the bilayers deposited at 798 K, it was observed a better coupling between the FeRh and Fe layers in comparison to samples deposited at 913 K, favoring an increase in the coercive field and the remanence magnetization.