Thesis (Ph. D.)--University of Wisconsin--Madison, 1969. / Typescript. Vita. Description based on print version record. Includes bibliographical references.

Thesis--Wisconsin. / Vita. Includes bibliographical references (leaves 218-224).

Thesis--Wisconsin. / Vita. Includes bibliographical references (leaves 186-190).

Bielefeld, University, Diss., 2003.

Berlin, Humboldt-Universiẗat, Diss., 2001.

Th.--Sci. phys.--Grenoble 1, 1980. N°: 10. / Extr. en partie du Journal de physique. Colloque C6, 39, 1978, 907-911 et de Journal of magnetism and magnetic materials, 17-19, 1980.

The question of the self-consistency of spin wave theory as applied to different spin arrangements in magnetically ordered crystals has been reinvestigated. A set of equations, involving the probabilities of finding a given number of spin deviations at a given site first proposed by Van Kranendonk and Van Vleck (1958) in connection with a simple cubic antiferromagnet at a temperature of 0°K, is generalised and solved exactly for an arbitrary temperature. Two sets of equations are solved both for the case of a simple cubic antiferromagnet and for more general spin arrangements, collectively referred to as spiral spin arrangements. In solving for the probabilities a method is developed for easy calculation of the thermal average of certain functions of number operators. Finally, numerical results are given for some probabilities connected with: (i) the simple cubic antiferromagnet and (ii) a model of the rare earth metal, dysprosium. The latter is of some interest in view of the investigations of spiral spin arrangements in recent years. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The yields of the reactions 12C(α, α ')12C* to the T=0 state at 12.71 MeV (Jπ=1+ ) and the T=l state at 15.11 MeV (Jπ=1+ ) were measured by detecting the decay of these levels to the ground state by gamma emmission. A 90° (lab) yield curve from threshold to Eα= 27.0 MeV was obtained for each reaction. Both states have to be populated via an unnatural parity process and in addition the population of the 15.11 MeV level is isospin forbidden. Nevertheless, excitation of both levels is unambiguously detected. Although the ratio of the yields has a considerable energy dependence ( 1%<̲δ15.11/ δ 12.71<̲ 20%), conclusive evidence is shown for the breaking of isospin in l60*(Ex = 24.0 to 27.3 MeV). The 15.11 MeV yield curve had considerable structure, suggesting the formation of interimmediate states in 16₀* . While the yield of the 12.71 MeV gamma ray also showed evidence of structure, it was not as . dramatic as the 15.11 MeV gamma ray. The yield of the reaction 10B(a ,dy)12C* to the 12.71 and 15.11 levels was also measured. If the outgoing particle is a true deuteron and not an unbound n-p pair, the population of the i5.ll is isospin forbidden. Contrary to the 15.11 and 12.71 yields in 12C(a , a’)12C*f no resonant structure was found ln either the 12.71 or 15.11 yields; it is suggested that the reactions proceed through an isospin allowed sequence. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Employing the semiclassical form of the density operator theory of dynamic processes, the transient nuclear spin behavior is analyzed for a range of motional parameters of significance for biological interpretations of nuclear magnetic relaxation data. Only relaxation which results solely from the reorientational modulation of the various spin couplings is considered. The bath correlation functions which enter into the theory are assumed to be completely characterized by two unique motional constants (a dynamic symmetric top approximation). The effects of slow, anisotropic modulation of spin-spin and spin-molecule interactions on T₁, T₂, T₁ ratios, T₂ ratios, and Overhauser enhancements are discussed. It is rationalized that in general, any parameter dependent upon the spectral density at zero frequency is independent of the magnitude of the asymmetry in the motion. Likewise, parameters independent of the near-zero frequency spectral component often are sensitive solely to the magnitude of the motional asymmetry. These considerations are extended to multispin systems and spin systems where nuclear magnetic relaxation proceeds by competing interactions characterized by nonvanishing interference or cross-correlation functions. In general, one cannot define unambigiously a unique T₁ or T₂ in such a case as the predicted decay is multi-(non)exponential. The spin behavior in such a situation is thoroughly analyzed and many intriguing predictions are presented. It is seen that the failure of a white spectral density approximation or a single exponential decay of the molecular correlation function often leads to predictions of extreme nonexponentiality of the magnetization decay. While the results of these calculations are of general interest, they are especially pertinent for those concerned with biological applications of NMR. Finally, the initial concepts are extended to a discussion of the potentially powerful Perturbed Angular Correlation experiment where it is shown that the coincidence counting rate will in general be influenced by anisotropic modulation of the quadrupolar perturbation. It is emphasized that a conventional interpretation of relaxation data is impregnated with hidden, "extreme-narrowed", reasoning. Extensive figures are provided which not only facilitate experimental application of the calculations, but also provide striking evidence for the caution which must be exercised in any biodynamical interpretation of nuclear spin relaxation. / Science, Faculty of / Chemistry, Department of / Graduate

<p>The spin of an electron often misleadingly interpreted as the classical rotationof a particle. The quantum spin distinguishes itself from classicalrotation by possessing quantized states and can be detected by its magneticmoment. The properties of spin and its collective behavior with otherfundamental properties are fascinating in basic sciences. In many aspectsit offers scope for designing new materials by manipulating the ensemblesof spin. In recent years attention towards high density storage devices hasdriven the attention to the fundamental level were quantum physics rules.To understand better design of molecule based storage materials, studies onspin degrees of freedom and their coupling properties can not be neglected.</p><p>To account for many body effect of two or more electrons consistent withrelativity, an approximation like the Breit Hamiltonian(BH) is used in modernquantum chemical calculations, which is successful in explaining the splitin the spectra and corresponding properties associated with it. Often differenttactics are involved for a specific level of computations. For example themulti-configurational practice is different from the functional based calculations,and it depends on the size of the system to choose between resourcesand accuracy. As the coupling terms offers extra burden of calculating theintegrals it is literally challenging.</p><p>One can readily employ approximations as it suits best for the applicationoriented device computations. The possible methods available in the literatureare presented in chapter 2. The theoretical implementations of couplingfor the multi-reference and density functional method are discussed in detail.The multi-reference method precedes the density functional methodin terms of accuracy and generalizations, however it is inefficient in dealingvery large systems involving many transition elements, which is vital formolecule based magnets as they often possess open shell manifolds. On theother hand existing density functional method exercise perturbations techniqueswhich is extremely specialized for a specific system - highly coupledspins.</p><p>The importance of spin-spin coupling(SSC) in organic radical-Oxyallyl(OXA)was systematically studied with different basis sets and compared with asimilar isoelectronic radical(TMM). The method of spin-spin coupling implementationsare also emphasized. Similar coupling studies were carriedivout for the species HCP and NCN along with spin-orbit coupling(SOC).The splitting of the triplet states are in good agreement with experiments</p>