Call number: LD2668 .T4 1979 H66 / Master of Science

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published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

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The motion of domain walls due to the spin torque generated by coherent carrier transport is of considerable interest for the development of spintronic devices. We model the charge and spin transport through domain walls in ferromagnetic semiconductors for various systems. With an appropriate model Hamiltonian for the spin– dependent potential, we calculate wavefunctions inside the domain walls which are then used to calculate transmission and reflection coefficients, which are then in turn used to calculate current and spin torque. Starting with a simple approximation for the change in magnetization inside the domain wall, and ending with a sophisticated transfer matrix method, we model the common π wall, the less–studied 2π wall, and a system of two π walls separated by a variable distance. We uncover an interesting width dependence on the transport properties of the domain wall. 2π walls in particular, have definitive maximums in resistance and spin torque for certain domain wall widths that can be seen as a function of the spin mistracking in the system — when the spins are either passing straight through the domain wall (narrow walls) or adiabatically following the magnetization (wide walls), the resistance is low as transmission is high. In the intermediate region, there is room for the spins to rotate their magnetization, but not necessarily all the way through a 360 degree rotation, leading to reflection and resistance. We also calculate that there are widths for which the total velocity of a 2π wall is greater than that of a same–sized π wall. In the double–wall system, we model how the system reacts to changes in the separation of the domain walls. When the domain walls are far apart, they act as a spin–selective resonant double barrier, with sharp resonance peaks in the transmission profile. Brought closer and closer together, the number and sharpness of the peaks decrease, the spectrum smooths out, and the domain walls brought together have a transmission spectrum with many of the similar features from the 2π wall. Looking at the individual walls, we find an interesting interaction that has three distinct regimes: 1) repulsion, where the left wall moves to the left and the right wall to the right; 2) motion together, where the two walls both move to the right, even at the same velocity for one special value of separation; and 3) attraction, where the left wall moves to the right and the right wall moves to the left. This speaks to a kind of natural equilibrium distance between the domain walls. This is of major interest for device purposes as it means that stacks of domain walls could be self–correcting in their motions along a track. Much experimental work needs to be done to make this a reality, however.

No description available.

Mycobacterial cell wall components have been shown to elicit a range of immunological responses in mammalian hosts. A family of cell wall antigens, the phosphatidylinositol mannans (PIMs), have been shown to reduce allergic response in a murine model of allergic airway disease and have been suggested as potential therapeutic agents. Isolation and characterisation of these compounds is not facile. To confirm the structure of PIMs a number of phosphatidylinositols (PIs), 1a-c, PIM1s 2a, 2d and 2e, and AcPIM1s, 2g and 2f, were prepared to allow assignment of the acylation pattern of natural products and for evaluation in immunological assays. As the natural products include 19:0 acylation in the form of (R)-tuberculostearoyl residues, a source of (R)-tuberculostearic acid was needed. To this end, an efficient synthesis of (R)-tuberculostearic acid from (S)-citronellol, utilising a copper-catalysed cross-coupling reaction and a modified Julia olefination, was developed. This material was incorporated into diacylglycerols prepared from (R)-benzyl glycidol. A protected myo-inositol derivative, 188, and two protected pseudo-disaccharides, 10 and 241, were prepared from myo-inositol via desymmetrisation utilising a camphylidene acetal. These were coupled with diacylglycerols via a phosphate ester and deprotected to give PIs, PIM1s and AcPIM1s. Mass spectrometry studies were undertaken on the PIs, 1a-c, PIM1s 2a, 2d and 2e, and AcPIM1s, 2g and 2f which structures that have been established by chemical synthesis. Comparison of these data with those reported for natural PIs and PIMs containing 19:0 ((R)-tuberculostearoyl) and 16:0 (palmitoyl) acyl groups unequivocally established that the 19:0 residue was located at the sn-1 and the 16:0 at the sn-2 position of the glycerol moiety in nature.

Bibliography: leaves 129-151. / xiv, 151 [65] leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 1999