In this thesis a consistent multipole theory is used to describe light propagation in nonabsorbing magnetic cubic and uniaxial crystals to the order of electric octopoles and magnetic quadrupoles. The first chapter extends Maxwell's equations for a vacuum to their macroscopic form in matter by including bound-source contributions as multipole expansions. From these the corresponding forms for D and H are obtained, which ensure origin-independence of Maxwell's equations. A multipole eigenyalue equation describing light propagation in a source-free homogeneous medium is then derived, which is the basic equation applied in this thesis. In the second chapter it is shown how, from the multipolar form of the propagation equation for transverse waves, expressions can be derived for the various birefringences that may be exhibited in macroscopic platelets of the medium, as introduced by Jones in the formulation of his M-matrix. The following chapter presents the derivation, by means of first-order perturbation theory, of the quantum mechanical expressions for the polarizability tensors which enter the eigenvalue wave equation. The origin independence of the expressions for the various observable quantities is then established. In the fourth chapter the independent components of the polarizability tensors are calculated for two selected crystal point groups, namely 622 and 432, by way of illustration. In chapter five the components calculated in the manner illustrated in the previous chapter are presented in tabular form. The Jones method outlined in chapter two is then applied to the crystal point group 6m2, again as an illustration of the method used to determine the optical effects displayed by this point group. Chapter five concludes with a table containing a listing of the predicted optical effects calculated in this way for all of the magnetic uniaxial and cubic point groups. The thesis concludes with chapter six, in which a summary of the results of the work undertaken is given, together with a discussion of factors influencing measurements of the predicted optical effects. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1997.

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ESR results for DEM(TCNQ)₂ and for MEM(TCNQ)₂ are presented as examples of TCNQ salts with and without level crossing effects. In the case of DEM(TCNQ)₂ we are performing ESR on a system with two types of spins. The latter are due to the two kinds of stacks of the acceptor TCNQ molecules in DEM(TCNQ)₂. The level crossing occurs when the g value of these two kinds of electrons are the same. This is compared to the case of MEM(TCNQ)₂ where there is only one kind of TCNQ stack and consequently no level crossing effect. It is found that g values and susceptibilities of the ESR spectra for DEM(TCNQ)₂ can be fitted very well to an interaction between the stacks of the form J ∑i,j,Si,Sj; with J > 0. This gives an antiferromagnetic coupling between every spin on one type of stack with every spin on the other type of stack. This type of interaction is also in qualitative agreement with the published results for HMM(TCNQ)₂. The experimental results in DEM(TCNQ)₂ and MEM(TCNQ)₂ also show that there are small but significant differences in the g tensors when the temperature or the crystalline environment are changed, and consequently the g tensor in these compounds does not depend only on the orientation of TCNQ molecule in the magnetic field as previously assumed. These differences in g are typically less than 2 x 10⁻⁴. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The archetypal high temperature superconductor Bi₂Sr₂CaCu₂O[subscript[8+δ]] has been extensively investigated. However, until now, little has been known about the behaviour of the magnetic vortices inside the Vortex Glass and liquid state. µSR measurements have shown a negative skewness for the field probability distributions in these regimes. Such a negative skewness has only recently been explained as being a direct consequence of three-body correlations between vortices in a similar layered superconductor. With a new understanding and knowledge of the physics of these systems, it is instructive to re-visit the superconductor Bi₂Sr₂CaCu₂O[subscript[8+δ]] to explain the evolution of these three-body correlations occurring here. Comparing this with the ion-irradiated superconductors (of the same Bi₂Sr₂CaCu₂O[subscript[8+δ]] material), allows one to observe how three-body correlations between vortices evolve differently to that in the pristine material. Moreover, in the region of the macroscopic irreversibility line, entropically driven disorder exists below the matching field B[subscript[ϕ]] , whilst there is the appearance of relatively straight vortex lines at fields above B[subscript[ϕ]] . Such phenomena suggest a significant di fference in the evolution of three-body correlations compared with the unirradiated material. There has been much work conducted on the interplay between superconductivity and magnetism in materials of reduced dimensions. Work presented here on the ferromagnet/superconductor trilayer system (Permalloy/Nb/Permalloy) has shown a novel magnetic profile at the interface between the ferromagnetic and superconducting boundary, where, contrary to what is expected, the magnetism appears to be significantly suppressed at the interface before increasing towards the centre of the Nb layer.

This thesis investigation concerns the optical and nonlinear electrical properties of n-InSb. Two specific areas have been studied. First is the magneto-optical study of magneto-donors, and second is the nonlinear dynamic study of nonlinear and chaotic oscillations in InSb. The magneto-optical study of InSb provides a physical picture of the magneto-donor levels, which has an important impact on the physical model of nonlinear and chaotic oscillations. Thus, the subjects discussed in this thesis connect the discipline of semiconductor physics with the field of nonlinear dynamics.

[by] J.M. Luttinger and L. Tisza. / "Reprinted from the Physical review, vol. 70, nos. 11 and 12, 954-964, Dec. 1 and 15, 1946." / Includes bibliographical references. / Contract OEMsr-262.

The previously unknown chemical and physical properties of the ternary rare-earth inter­metallic compounds, RETGe (RE=Sc, Y, La–Lu; T=Ag, Au), are investigated using a variety of experimental techniques. The RETGe are found to crystallise in three basic different crystal structure types (CaIn2-, Fe2P-, and CeCu2-type derivatives).

Orientador: Antonio Manoel Mansanares / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-07T05:32:29Z (GMT). No. of bitstreams: 1 Tedesco_JulioCesarGuimaraes_M.pdf: 2257382 bytes, checksum: 5ce80fd32f944476c7b03fe5dfa792e1 (MD5) Previous issue date: 2006 / Resumo: O crescente estudo em materiais com largas bandas e absorção óptica e luminescência é devido à possibilidade de usá-los como fonte e radiação sintonizável. Os monocristais Cs2NaAlF6:Cr 3+e Cs2NaGaF6:Fe 3+ apresentam tais propriedades e, naturalmente, algumas propriedades físicas, tais como a estrutura cristalina, são aspectos decisivos para a atividade óptica nestes sistemas e devem ser melhor conhecidas. Este trabalho apresenta a caracterização dos monocristais Cs2NaAlF6 (dopado com 1% e Cr 3+) e Cs2NaGaF6 ( dopado em 1% e 10% e Fe3+) por meio de ressonância paramagnética eletrônica (Electron Paramagnetic Resonace - EPR). Nestes compostos, o íon Cr 3+(Fe3+) substitui o íon Al3+(Ga 3+) em dois sítios não-equivalentes com simetria axial com respeito ao eixo cristalográfico c. Os resultados obtidos permitem o estudo dos principais aspectos dos sítios de ocupação dos dopantes, tais como geometria e intensidade do campo cristalino, suas transições magnéticas mais prováveis. Os dados experimentais foram obtidos com um espectrômetro comercial de EPR operando em banda X à temperatura ambiente. Os espectros foram obtidos em diferentes orientações (direções) da amostra com respeito ao campo magnético aplicado em uma larga faixa angular. Os parâmetros espectrais (campo e ressonância, amplitude e largura de linha e ressonância) foram determinados pelo método dos mínimos quadrados ajustados com derivadas e lorentzianas, onde o número e linhas foi escolhido por inspeção visual. Com os campos e ressonância extraídos os espectros e a hamiltoniana do sistema, foi possível encontrar os parâmetros e campo zero ( D , a e F ) e as componentes o tensor g que melhor reproduzem o comportamento experimental. Devido ao elevado desvio no ajuste de alguns parâmetros espectrais (amplitude e largura de linha de ressonância) e à elevada dependência da intensidade das transições com o alinhamento a amostra na cavidade, foi possível determinar somente o módulo dos valores dos parâmetros de campo zero D, a e F. Além isto, os dados experimentais permitiram calcular, em alguns casos, somente valores limites os parâmetros e campo zero a e F. Consideramos serem necessárias medidas sob baixas temperaturas e a utilização e outra técnica, como ENDOR, para uma determinação mais precisa (além dos sinais) dos parâmetros citados, assim como a quantidade de dopante em cada sítio de ocupação / Abstract: The interest in materials with large bands of absorption and luminescence is due to the possibility of their applications as tunable solid state lasers. The crystals Cs2NaAlF6:Cr3+ and Cs2NaGaF6:Fe3+ present these properties and , naturally, some of their physical characteristics, such as the crystal field , are decisive for their optical activity and should be better investigated. This work presents a characterization of Cs2NaAlF6:Cr 3+single crystal (doped with 1%) an Cs2NaGaF6:Fe 3+single crystals ( doped with 1% an 10%) using electron paramagnetic resonance (EPR). In these compounds, the Cr3+(Fe3+) ions substitute Al3+ (Ga 3+) ions in two non-equivalent sites with axial symmetry with respect to the c crystallographic axis. The obtained results allow the study of the main aspects of the sites occupied by Cr3+(Fe 3+) ions, such as their geometry and intensity of crystal fiel. A commercial EPR spectrometer operating at X-ban frequencies and room temperature has been employed. Spectra at different orientations of the sample with respect to the applied magnetic field have been obtained for a large range of angles. The spectral parameters (resonance field , amplitude an linewidth) were determined from least square fits of the derivative of the Lorentzian lines. The number of lines in each spectrum was chosen by visual inspection. Using the resonance fields an the Hamiltonian of system, it was possible to find the zero fiel parameters that better reproduce the experimental behavior. Due to the large inaccuracy in the fitting an the large epen ence of transitions intensity on the sample alignment, it was not possible to determine the sign of the zero field parameters, only their magnitude. The experimental data permitted to calculate, in some cases, only the upper limit of the magnitude of a an F . We consider that studies at low temperature an the use of others techniques, like ENDOR, are necessary to increase the accuracy in the determination of the parameters (include their signs), as well as the determination of the amount of oping in each site / Mestrado / Ressonancia Magnetica e Relaxamento na Materia Condensada ; Efeitos Mosbauer ; Corr. Ang. Pertubada / Mestre em Física

Semiconductor devices are the building blocks of electronics and communication technology in the modern world. The charge, mass and spin of charge carriers in the semiconductor devices lay the foundations of the technology developments in the modern age. But to date only the electronic charge of the semiconductors has been exploited for such applications. The significance of the spin of charge carriers is completely ignored because in a semiconductor the half of the carriers are in spin-up state and the remainder are in spin-down state. A new electronics termed as spintronics, spin-transport based electronics, is focused to utilise the spin degree of freedom of the charge carriers in addition to its electronic charge. The devices based on these have the potential for various technological advancements like non-volatility, increased data processing speed, decreased electronic power consumption and increased integration densities as compared to the conventional semiconductor devices. In this study, the author intended to study the growth and properties of magnetic impurity doped antimony based III-V compounds and compare these results with those of the films grown by MBE. This thesis is organised into seven chapters. The first introductory chapter gives a brief review of the work on spintronics, diluted magnetic semiconductors, Ferromagnetic / paramagnetic semiconductor hybrid structures with special emphasis on the properties of antimonides which have already been reported in the literature. This is followed by the scope of the thesis. The second chapter deals with technical details of various instruments used in the present research work. Third chapter describes the growth and structural properties of bulk crystals grown by Bridgman method and thin films grown by liquid phase epitaxy (LPE). Bulk crystals of InSb and GaSb doped with magnetic elements such as Mn and Fe are grown with different doping concentrations. Thin films of InSb and GaSb doped Mn with different doping concentrations are grown by LPE. The grown crystals are processed by slicing, lapping, polishing and chemical etching methods. X-ray diffraction studies are carried out to confirm alloy formation and to find the change in lattice parameter if any. From the powder diffraction patterns, the lattice parameter is refined with the help of Retvield refinement program. A systematic change of lattice parameter with the incorporation of magnetic impurities into InSb and GaSb is observed. Scanning electron microscopy and energy dispersive x-ray analysis are carried out to identify the secondary phases and their composition respectively. Chapter 4 gives the detailed magnetotransport studies carried out on InSb and GaSb crystals doped with Mn and Fe. Also, the magnetotransport studies carried out on thin films grown by liquid phase epitaxy are presented here. This chapter is divided into three sections of which the first section deals with Mn doped bulk crystals of InSb and GaSb, the second section deals with Fe doped bulk crystals of InSb and GaSb and the third section deals with Mn doped InSb and GaSb films grown on GaAs by Liquid Phase Epitaxy. Temperature dependence of zero field resistivity, magnetoresistance and Hall measurements are carried out from 1.4 to 300K. All the samples show p type conduction throughout the temperature range studied except for Fe doped InSb. Mn doped crystals show negative magnetoresistance and anomalous Hall effect below 10K. Anisotropy in magnetoresistance is also observed at low temperatures in InMnSb crystals. On the other hand, Fe doped samples exhibit positive magnetoresistance throughout the temperature range and no anomalous Hall effect is observed. Chapter 5 describes the magnetic properties of bulk InMnSb, GaMnSb, InFeSb and GaFeSb crystals so also the thin films of InMnSb/GaAs. DC magnetization measurements are carried out in the temperature range 2 - 300K. The Mn doped InSb and GaSb crystals as well as InMnSb/GaAs films, show a magnetic ordering below 10K which could arise from the InMnSb and GaMnSb alloy formation. Also, saturation in magnetization observed even at room temperature suggests the existence of ferromagnetic MnSb clusters in the crystals which has been verified by scanning electron microscopy studies. In Fe doped InSb crystals, the temperature dependent DC magnetization shows irreversibility under field cooled and zero field cooled conditions below 12K, suggesting a spin glass-like behaviour. Also, magnetization measurement shows the coexistence of ferromagnetic and paramagnetic phases throughout the temperature range studied. Existence of ferromagnetic phase could arise from secondary phases Fe1-xInx or FeSb2 present in the crystal as clusters and paramagnetic phase could arise from the randomly distributed Fe atoms in the InSb matrix. Fe doped GaSb crystals show interesting magnetic property that arises from the FeGa alloy (secondary phase) present in it. The EPR studies on Ga0.98Mn0.02Sb cluster-free (?) crystal suggest that the dominant Mn impurity in GaMnSb is Mn2+ (d5), described as ionized acceptor A−. This conclusion was derived from EPR experiments, which reveal a strong absorption line with an effective g factor very close to 2.00, the value typical for centre A−. The absence of EPR signal typical for neutral Mn acceptor A0 suggests that this center is absent in the crystal under investigation. The observed behavior is similar to that of Ga1-xMnxAs and In1-xMnxAs epilayers. EPR studies also reveal that the competition between antiferromagnetic and ferromagnetic phases exists in the studied crystal. Chapter 6 describes the optical measurements carried out on bulk Ga1-xMnxSb crystals and their films with different Mn doping concentrations. FTIR studies are carried out in the temperature range 4 - 300 K. From the FTIR studies, it is found that intra valance spin – orbit splitting band absorption is dominant compared to the fundamental absorption in doped crystals. In higher doped crystals (x > 0.01), fundamental band absorption merges with split-off band and could not be resolved. Free carrier absorption studies are also carried out in the energy range below the band gap. FTIR studies on GaMnSb/GaAs films suggest band gap narrowing effect due to Mn doping. Furthermore the Photoluminescence measurements are carried out in the temperature range 10 – 300 K for all the Mn doped GaSb crystals. PL studies also support the band gap narrowing and band filling effects. A comprehensive summary of this research investigation and scope for the further work are presented in the last chapter.