published_or_final_version / abstract / Physics / Master / Master of Philosophy

Detailed magnetometry and polarized neutron reflectometry studies were conducted on MnSi thin films grown epitaxially on Si(111) substrates. It is demonstrated that with an in-plane applied field H || [110], a broadly stable skyrmion phase exists at elevated temperatures and fields. Magnetometry and transport measurements with an out-of-plane applied field H || [111] prove that no skyrmion phase exists in this geometry. However, Hall effect measurements in this geometry show unexpected evidence of a topological Hall effect. This can be explained with a multi-dimensionally modulated cone phase, which proves that contrary to recent literature, a topological Hall effect is not sufficient proof of skyrmions. The results of this thesis represent a significant step towards a technologically relevant material in which skyrmions are broadly stable. A material of this type could be used in novel magnetic storage devices and signi ficantly impact our future computing capabilities.

This thesis presents the modeling and design of memory cells for Spin Torque Transfer Magnetoresistive Random Access Memory (STT-MRAM). The theory of operation of STT-MRAM cells is explored, and a model to predict the transient behaviour of STT-MRAM cells is presented. A novel three-terminal Magnetic Tunneling Junction (MTJ) and its associated cell structure is also presented. The proposed cell is shown to have guaranteed read-disturbance immunity, as during a read operation the net torque acting on the storage cell always acts to refresh the stored data in the cell. A simulation study is conducted to compare the merits of the proposed device against a conventional 1 Transistor, 1 MTJ (1T1MTJ) cell, as a well as a differential 2 Transistors, 2 MTJs (2T2MTJ) cell. Simulation results confirm that the proposed device offers disturbance-free read operation while still offering performance advantages over conventional cells.

This thesis presents the modeling and design of memory cells for Spin Torque Transfer Magnetoresistive Random Access Memory (STT-MRAM). The theory of operation of STT-MRAM cells is explored, and a model to predict the transient behaviour of STT-MRAM cells is presented. A novel three-terminal Magnetic Tunneling Junction (MTJ) and its associated cell structure is also presented. The proposed cell is shown to have guaranteed read-disturbance immunity, as during a read operation the net torque acting on the storage cell always acts to refresh the stored data in the cell. A simulation study is conducted to compare the merits of the proposed device against a conventional 1 Transistor, 1 MTJ (1T1MTJ) cell, as a well as a differential 2 Transistors, 2 MTJs (2T2MTJ) cell. Simulation results confirm that the proposed device offers disturbance-free read operation while still offering performance advantages over conventional cells.

Making spintronic devices is a hot topic for future technical development. In this work the non-equilibrium dynamics of a single spin in a tunnel junction is analyzed and numerically simulated. This is done in order to understand the dynamics of e.g. a magnetic molecule between two metal contacts for future spintronic devices. The work starts with looking at the system in a many-body theory picture in order to derive the interesting properties of the system. An initial solution for the system is analytically calculated as well as for the dynamic case. The dynamic has then been numerically simulated in order to get the time evolution of the system. The results showed that the dynamics of the molecular spin induced a spin dependent charge and spin currents in the system and that the currents could be used to control the molecular spin. It showed qualitatively how different parameters, for example coupling strength, effect the system and what to consider when designing a system similar to this.

Thesis (Ph. D.)--University of Hong Kong, 2007. / Also available in print.

Thesis (Ph.D.)--University of Wollongong, 2006. / Typescript. Includes bibliographical references: leaf 106-116.

Thesis (Ph.D.)--University of Western Australia, 2006.

Thesis (M.Sc.). / Written for the Dept. of Physics. Title from title page of PDF (viewed 2008/12/04). Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.