New torques acting on magnetization in metallic ferromagnets, accompanied by new terms to the Landau-Lifshitz-Gilbert (LLG) equation which governs GHz magnetization dynamics, are important for both the fundamental understanding of magnetism and applications in magnetoelectronic devices. In this thesis, we have carried out experimental investigations of several proposed novel torques acting on magnetization dynamics using broadband ferromagnetic resonance (FMR) between 2-26 GHz. The FMR technique is well-suited for materials studies, as it investigates unpatterned (sheet-level) films with relatively high throughput, enabling comparison of the response of several room-temperature, device-relevant ferromagnetic alloys (e.g. Ni₇₉Fe₂₁, or ‘Py’, Co, and CoFeB.) The common aspect of the torques which we have investigated by FMR is their origin in nonequilibrium spin populations, related to spin transfer torque. In Chapter 3 we have identified intrinsic “inertial” torques on magnetization, significant only at very high frequencies (up to 300 GHz), where the electron population cannot quite keep pace with the precession of magnetization. In Chapters 4 and 5 we have studied torques from “pumped” pure spin current due to the texture of precessing magnetization (intralayer spin pumping) and the precession of noncollinear magnetizations in trilayer structures (spin pumping). These three studies extend understanding of magnetism and magnetization dynamics at room temperature, and in limits of high speed and small dimension relevant for emerging applications.

Os fosfolipídios são moléculas anfifílicas que constituem o principal componente das membranas celulares. Na presença de água e para urna concentração suficientemente alta do fosfolipídio, as moléculas se auto organizam formando bicamadas separadas por água. Dentro das bicamadas, e dependendo da temperatura e a concentração, os fosfolipídios podem apresentar diferentes empacotamentos, dando origem a diferentes mesofases. Três mesofases são bem conhecidas: L IND. P IND. e L IND.. As mesofases L IND. e L IND. apresentam as bicamadas planas, porém, a diferença entre as duas está em que a fase L IND. apresenta as cadeias hidrocarbonadas ordenadas, com uma certa inclinação em relação à normal às bicamadas, e na fase L IND. as cadeias hidrocarbonadas estão completamente desordenadas. A fase P IND. conhecida como fase \"ripple\", apresenta uma ondulação periódica das bicamadas e as cadeias carbônicas com um certo grau de ordenamento. Existe na literatura urna grande discussão acerca da origem das mesofases lamelares, porém não existe um trabalho sistemático que permita caracterizar experimentalmente em forma completa as transições de fase entre as mesofases lamelares. Neste trabalho investigamos as transições de fases no sistema DMPC/água (dimiristoil-fosfatidil-colina/água), na região do diagrama de fases onde são observadas as fases L IND. P IND. e L IND.. Utilizamos as técnicas de calorimetria DSC e espalhamento de Raios X para levantar o diagrama de fases do sistema DMPC/água, e estudamos o comportamento da entalpia das diferentes transições de fase em função da concentração. Mediante microscopia de luz polarizada e espalhamento de Raios X caracterizamos o ordenamento induzido em amostras submetidas ao processo de \"shear\" . O procedimento permite observar por espalhamento de Raios X o comportamento da ordem no plano das bicamadas. Esse estudo permitiu também o acompanhamento do espaçamento entre as bicamadas nas transições de fase L IND. P IND. e P IND. L IND.. Tradicionalmente, em modelos teóricos, as transições L IND. P IND. e P IND. L IND. são tratadas corno de primeira ordem. Alguns modelos propõem que estas linhas de transição se encontram num ponto de Lifshitz. Mediante calorimetria de alta resolução estudamos o comportamento do calor específico em diferentes regiões do diagrama de fases. A transição P IND. L IND. para uma concentração de 28% em peso de água, não mostra a forma esperada para transições de primeira ordem, embora apresenta uma certa histerese. Encontramos que a primeira correção de \"scaling\" descreve bem o comportamento do calor específico a até uma temperatura onde este, claramente mostra-se arredondado. Essa região arredondada pode ser entendida no contexto das transições que envolvem ordem hexática, devido ao acoplamento entre o \"tilt\" e a ordem hexagonal. Essa observação é reforçada pela ordem bidimensional observada por espalhamento de raios-x. Finalmente investigamos a existência de fase \"ripple\" em outro fosfolipídio, DMPG (dimiristoil-fosfatidil-glicerol) que difere do DMPC apenas na cabeça polar. / Phospholipids are amphiphilic molecules that constitute the main component of the cellular membranes. In the presence of water and for concentrations sufficiently high of the lipid, the molecules self-assemble in bilayers separated by water. Inside the bilayers, and depending on the temperature and concentration, the phospholipids can present different packings, giving origin to different mesophases. Three mesophases are well-known: L´, P´ and La . The mesophases L´ and La present planar bilayers, even so, the difference between them is in the hydrocarbons chains. The L´ presents the chains orderly, with a certain tilt related to the normal of the bilayers, and in the La phase the chains are completely disordered. The P´ phase, known in the literature as ripple phase, presents periodic undulation of the bilayers and the carbonic chains with a certain degree of order. There is a great discussion in the literature concerning the origin of the lamellar phases, even though there is no systematic experimental work characterizing the phase transitions between lamellar phases. In this work we investigated the phase transitions in the DMPC/water system (dimiristoyl- phosphatidyl-choline), in the area of the phase diagram where the L´ P´, and La phases are observed. We used the calorimetric DSC technique and x-ray scattering to construct the phase diagram of DMPC/water, and we studied the behavior of the enthalpy associated to the different transitions as a function of the concentration. By means of polarized light microscopy and x-ray scattering we characterized the order induced in samples submitted to shear. The procedure allows us to observe the behavior of the in-plane order in the lamelas by means of x-ray scattering. This study also allowed to see the behavior of the lamellar spacing in the L´ -> P´, and P´, -> La phase transitions. Usually, the L´ -> P´, e P´ -> La are treated as first order transitions. Some models proposes that this transition lines encounters in a Lifshitz point. With high calorimetric resolution we study the behavior of the specific heat in different regions of the phase diagram. The P´ -> La transition for 28% of water, doesn\'t show the expected first order behavior. Instead of that we find that the first order correction to scaling succeeded to describe the specific heat near the transition, but clearly, de experimental data shows some rounding region. This rounded region can be understood in the context of the transitions involving hexatic order, where the tilt and the hexagonal ordering are coupled. This observation is reinforced by the 2D order observed by x ray scattering. We also investigated the existence of the \"ripple\" phase in another phospholipid, DMPG (dimiristoyl-phosphatidyl-glycerol) that just differs from DMPC in the polar head.

The Kibble-Zurek mechanism (KZM) was originally proposed to describe the evolution and "freezing" of defects in the early universe, but later it was generalized to study other quantum and classical systems driven by a varying parameter. The basic idea behind the KZM is that, as long as the changing rate (velocity) of the parameter is below a certain critical velocity, 𝑣_crit, the system will remain adiabatic (for isolated quantum systems) or quasi-static (for classical systems with a heat bath). The nonequilibrium finite-size scaling (FSS) method based on KZM has been exploited systematically. Through applying the scaling hypothesis, we can extract the critical exponents and study the dynamic properties of the system. In the first few chapters of this dissertation, we discuss the applications of KZM in several classical systems: first, we study the dynamics of 2D and 3D Ising model under a varying temperature as well as a varying magnetic field. Secondly, we examine the classical ℤ₂ gauge model, in which we show that KZM also works for topological phase transitions. Moreover, we also investigate the dynamics of other models with topological ordering only at T=0, where KZM cannot be applied. Lastly, we explore the 2D Ising spin glass with bimodal and gaussian couplings. With bimodal couplings, we find dual time scales associated with the order parameter and the energy correspondingly, while in the gaussian case one unique time scale is involved. The systems mentioned above are all classical and the dynamics are approached through simulated annealing (SA), in which thermal fluctuations drives systems to explore the energy landscape in finding the ground state. In the last chapter, we explore the efficiency of Quantum Annealing (QA) on a fully-connected spin glass (or Sherington-Kirkpatrick model) with a transverse field. QA is the counterpart of SA, where quantum fluctuations drive the system toward the ground state when the quantum terms are reduced. QA is currently widely explored as a paradigm for quantum computing to solve optimization problems. Here we compare the scaling of the dynamics (with system size) of the fully-connected spin glass through QA versus SA.

This dissertation presents an investigation on the effects of large scale roughness on the properties of giant magnetoresistive multilayers. The large scale roughness (sigmarms > 5 nm) is introduced into giant magnetoresistive thin films through the substrate. Current-in-plane (CIP) and current-perpendicular-to-the-plane (CPP) thin films were deposited by dc magnetron and triode sputtering. All films were characterized for roughness, magnetic and electronic behavior.;Our research on both pseudo spin valves and exchange-biased spin valves shows that long length scale roughness does not have a significant detrimental effect on GMR thin films. For the CIP films, we find that a decrease in GMR correlates to an increase in minimum film resistivity. as the minimum resistivity increased, the maximum resistivity increased linearly with a slope ∼1. This suggests that the decrease in GMR may primarily be an effect of increased spin-independent scattering resulting from the increased film roughness. The CPP films showed a similar relationship between minimum and maximum resistance. Studying the effect of such large scale substrate roughness is important for applications in which GMR multilayers are deposited on non-standard substrates and buffer layers including flexible media.

A positive muon can be considered an isotope of hydrogen due to similarities in spin and charge. For metal hydride systems, the muon enters the sample "as the last hydrogen added," and competes for the same sites as the hydrogen atoms. to observe the site competition and diffusion of both particles (muon and proton), several FCC metal hydrides, TiH{dollar}\sb{lcub}1.83{rcub}{dollar}, TiH{dollar}\sb{lcub}1.97{rcub}{dollar}, TiH{dollar}\sb{lcub}1.99{rcub}{dollar}, YH{dollar}\sb{lcub}1.77{rcub}{dollar}, YH{dollar}\sb2{dollar}, ZrH{dollar}\sb{lcub}1.94{rcub}{dollar}, and LaH{dollar}\sb{lcub}2.06{rcub}{dollar}, were studied using transverse-, zero-, and low longitudinal-field {dollar}\mu{dollar}SR. The low temperature region results indicate that the muon predominately occupies octahedral sites for the FCC metal hydrides in this study. The probability for a muon to occupy a tetrahedral site in titanium and zirconium hydrides at these temperatures is proportional to the vacancy concentration. Whereas the probability for T site occupation in yttrium hydride is proportional to the number of protons not occupying these sites which increases with hydrogen concentration. Muon T site occupancy below room temperature for LaH{dollar}\sb{lcub}2.06{rcub}{dollar} was not observed and was not expected since these sites are occupied by protons. Around 300 K, the muon diffuses over interstitial O sites to vacancies in the H sublattice of TiH{dollar}\sb{lcub}1.99{rcub}.{dollar} The vibration of the hydrogen lattice is found to be the mechanism responsible for the activation of the muon out of the O site. Above room temperature, the muon occupies tetrahedral sites in yttrium and titanium hydrides. at high temperatures, the field-correlation time for a muon in titanium and yttrium hydrides is approximately one to two orders of magnitude greater than for a proton as measured by NMR. The results of a Monte Carlo simulation indicate that the presence of the muon inhibits the motion of the nearest-neighbor protons at high temperatures. The dynamics of the proton spins are observed by zero- and low longitudinal-field {dollar}\mu{dollar}SR through the oscillation of the muon polarization at long times for a static muon in a T or O site. This observation is not predicted by the Kubo-Toyabe treatment for a stationary muon.

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An efficient method for calculating NMR lineshapes from anisotropic second rank tensor interactions is presented. The algorithm produces lineshapes from asymmetric tensors by summing those from symmetric tensors. This approach significantly reduces the calculation time, greatly facilitating iterative nonlinear least squares fitting of experimental spectra. This algorithm has been modified to produce partially relaxed lineshapes and spectra of partially ordered samples.;Calculations for rapidly spinning samples show that spin-lattice relaxation time ( T1Z ) anisotropy varies with the angle between the spinning axis and the external field. When the rate of molecular motion is in the extreme narrowing limit, measurement of T1Z anisotropies for two different values of the spinning angle allows the determination of two linear combinations of the three static spectral densities, J0(0), J1(0) and J2(0). Experimental results for ferrocene demonstrate the utility of these linear combinations in the investigation of molecular dynamics with natural abundance 13C NMR. For ferrocene-d 10, deuteron T1Z and quadrupolar order relaxation time ( T1Q ) anisotropies, along with the relaxation time of the 13C magic angle spinning (MAS) peak, provide sufficient information to determine the orientation dependence of all three individual spectral densities. The experimental results include the first determination of J 0(0) in a solid sample.;A variety of experimental techniques were used in an investigation of the polyimides LaRC-IA, LaRC-TPI and LaRC-SI and related model compounds. Magic angle spinning was used to acquire 13C isotropic chemical shift spectra of these materials. The spectra were assigned as completely as possible. In addition, the principal components of some shielding tensors were measured using variable angle correlation spectroscopy. of those studied, LaRC-SI is the only polymer that is soluble. However, after it is heated past its glass transition temperature, LaRC-SI becomes insoluble. Experiments were performed in an attempt to identify causes of this behavior. 1H and 13C NMR spectra of soluble and insoluble LaRC-SI are significantly different when magnetization from nuclei in rigid regions of the polymer is suppressed. Hydration studies of LaRC-SI and LaRC-IA show that absorbed water plasticizes these polymers.

In this thesis, we explore two stochastic techniques to study properties of materials in realistic systems. Specifically, the kinetic Monte Carlo (KMC) method is utilized to study the crystal growth process of ferroelectric materials and the quantum Monte Carlo (QMC) approach is used to investigate the ground state properties of atoms and molecules.;In the growth simulations, we study the growth rates and chemical ordering of ferroelectric alloys using an electrostatic model with long-range Coulomb interactions. Crystal growth is characterized by thermodynamic processes involving adsorption and evaporation, with solid-on-solid restrictions and excluding diffusion. A KMC algorithm is formulated to simulate this model efficiently in the presence of long-range interactions. The growth process is simulated as a function of temperature, chemical composition, and substrate orientation. We carried out the simulations on two heterovalent binaries, those of the NaCl and the Ba(Mg1/3Nb2/3))O3(BMN) structures. Compared to the simple rocksalt ordered structures, ordered BMN grows only at very low temperatures and only under finely tuned conditions. For materials with tetravalent compositions, such as (1-x)Ba(Mg 1/3Nb2/3))O3 + x BaZrO3 (BMN-BZ), the model does not incorporate tetravalent ions at low-temperature, exhibiting a phase-separated ground state instead. at higher temperatures, tetravalent ions can be incorporated, but the resulting crystals show no chemical ordering in the absence of diffusive mechanisms.;In the second part of the thesis, we present results from an auxiliary field quantum Monte Carlo (AFQMC) study of ground state properties, in particular dissociation and ionization energy, of second-row atoms and molecules. The method projects the many-body ground state from a trial wavefunction by random walks in the space of Slater determinants. The Hubbard-Stratonovich transformation is employed to decouple the Coulomb interaction between electrons. A trial wave function is used in the approximation to control the "phase problem". We also carry out Hartree-Fock (HF) and Density Functional Theory (DFT) calculations for comparison to AFQMC results and to serve as starting wavefunctions for our AFQMC calculations. Results of dissociation energy are in excellent agreement with experimental values. Ionization energy errors are somewhat larger than those of other methods. We conclude with a discussion of several possible sources of error as well as a direction for the improvement.

For the first time, external uniaxial stress has been used in a (mu)('+)SR experiment. The stress dependences of the following parameters were obtained for Fe crystals: the muon precessional frequency, (nu)(,(mu)), the transverse (longitudinal) depolarization rates, 1/T(,2) (1/T(,1)), and F(,T)/F(,L), the ratio of the probabilities for the muon to find domains with transverse/longitudinal fields. The shift in (nu)(,(mu)) was -0.34 (+OR-) 0.023 MHz per 100 micro-strain along the -axis. Changes in other parameters depend on the sample history but they, in general, increase with stress.;External stress changes the muon occupational probability at each site which significantly affects the dipolar field averaged over interstitial sites of the same initial symmetry. This change in the averaged dipolar field is shown to be the main cause of the shift in (nu)(,(mu)). to calculate the dipolar field at each site, the finite extension of the muon probability density and displacement of neighboring host atoms around the site are explicitly taken into account. From the experimental results and the dipolar field calculation, it is possible to estimate the anisotropy of the double-force tensor, (P(,1)-P(,2)), for the muon in Fe. This clearly shows that in Fe, for reasonable muon wave function shapes, the muon is more likely to occupy the 4T(0) site configuration.;For a random distribution of domains among the six easy axes of Fe, the dipolar field averaged over a region of the sample should be zero. However, the external stress breaks this randomness and with a certain magnitude of tensile stress in the z-axis, domains will align along the (+OR-) z-directions. A muon with its initial spin aligned perpendicular to the z-axis does not distinguish the stress induced domain alignment from the saturation along the + or - z direction. The experimental result shows the same stress dependence of (nu)(,(mu)) for both the stress induced and the externally saturated domain alignments. as expected the change in (nu)(,(mu)) with low stress is very small without the application of an external saturation field. Also, the change in F(,T)/F(,L) is consistent with that in (nu)(,(mu)) indicating that this parameter is a good measure of the domain alignment.;Similar results were obtained for polycrystalline samples. The interpretation made on the single crystal result is applicable to these results and it is possible to explain why local strains in Fe tend to reduce the magnitude of (nu)(,(mu)).