Thesis (Ph. D.)--University of Wisconsin--Madison, 1938. / Typescript. Includes abstract and vita. Includes bibliographical references (leaves 85-86).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1971. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2006. / Includes bibliographical references (leaves 87-94). Also available in electronic version.

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Since its discovery in 1946 over 400 papers have been published on nuclear magnetic resonance of which more than 50% are related to problems in the structure of matter. This fact illustrates the scope of this comparatively new technique in the field of structural investigations. In addition nuclear magnetic resonance can give information concerning molecular motion in the solid state. The work reported in this thesis is concerned with this field of research. An account is given of the application of nuclear magnetic resonance to the study of single crystals of Urea and Rochelle Salt.

The phenomenon of nuclear magnetic resonance is closely related to the molecular beam experiments and to microwave spectroscopy. Its significant feature is that the magnetic resonance principle, first applied to the molecular beam technique, has been extended to solids, liquids and gases in their normal physical states. In addition to providing yet another important method of measuring nuclear magnetic properties, this newer technique gives a means of investigating the establishment of the thermal equilibrium which is essential to the methods of obtaining very low temperatures; further, the resonance absorption spectrum yields information of crystal structures, phase transitions in solids and information about hindered rotation of molecules in solids. Thus the phenomenon can be used to study certain problems of the solid state. This thesis gives an account of such an application.

It has been known since 1946 that energy can be absorbed from a radiofrequency field by the nuclear spins in bulk material placed in a uniform magnetic field. For this absorption of energy to be a continuous process it is necessary for the spins to have some thermal contact with the surrounding lattice, so that they can pass on the absorbed energy and then take part in further absorption. In general a nucleus can exchange energy with the lattice by means of interaction between its magnetic dipole moment and fluctuating magnetic fields supplied by the lattice, or by interaction between the electric quadrupole moment of the nucleus and fluctuating electric field supplied by the lattice. Either or both of these interactions can provide the relaxation mechanism which allows the nucleus to lose to the surrounding lattice the excess energy gained from the applied radiofrequency field in nuclear magnetic resonance absorption. This thesis describes a method of showing experimentally which of these interactions is dominant in providing the relaxation mechanism in cases where either mechanism can operate.

D.Phil. (Physics) / Most of previous magnetic investigations performed on uranium chalcogenides have been limited to polycrystalline specimens. To extend the knowledge on magnetization processes in uranium monosulphide, single crystals were grown. The magnetization of these single crystals was determined in the ferromagnetic and paramagnetic regions as a function of temperature (4-300 °K), field strength (0-20 k0e) and orientation ...

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In 1930, Bloch derived a formula for the temperature-dependence of the spontaneous magnetisation of a ferromagnetic substance (in the sense of the well-known Heisenberg model) valid asymptotically as the temperature T tends to zero. In 1936, Kramers rederived Bloch's formula using an entirely new approximate method. In 1937, Opechowski applied Kramers’ method to obtain, in addition to Bloch's T³′²-term in the expression for the magnetisation, two additional terms, in T² and T⁵′². In 1956, Dyson found a rigourous method for dealing with this problem. His result shows that there is no T²-term and the T⁵′²-term has a coefficient different from that found by Opechowski. In this thesis, some possibilities are investigated of modifying Kramers' method. In particular, the question is considered, which assumptions in Kramers' method are responsible for the above mentioned discrepancies. In Kramers' method, the partition function of the Heisenberg model is identified with the largest term in its power series expansion. The calculation of the largest term is in turn reduced to a certain random walk problem. This reduction of the problem to a random walk problem involves certain assumptions which we have not tried to modify in this thesis. What is new is a careful discussion of, and improvement on the solution of the random walk problem. The improved method of solving this problem leads to a cubic equation in P¹′², where P is a certain parameter with no single physical meaning. In chapters 6 and 7, a first approximation is obtained by omitting the term in P³′². The resulting quadratic equation in P¹′² leads to an expression for the spontaneous magnetisation containing no term in T² as in Dyson's formula. The solution of the complete cubic equation unfortunately leads to an expression for the spontaneous magnetisation, in which the term in T² reappears again. One obtains again Opechowski's result, except for a small modification of the coefficient of the T⁵′²-term; this is due to a better approximation for the factorials occuring in the calculations. This fact shows that Kramers’ random walk problem constitutes too crude an approximation of the actual problem. After the writing of this thesis was completed, Professor Opechowski found a way of modifying Kramers' method. The calculation of the partition function in the modified method is reduced to a slightly different random walk problem. The expression for the spontaneous magnetisation becomes then identical with Dyson's up to the T⁷′²-term inclusive. / Science, Faculty of / Physics and Astronomy, Department of / Graduate