5 research outputs found
High-Performance Energy-Efficient and Reliable Design of Spin-Transfer Torque Magnetic Memory
In this dissertation new computing paradigms, architectures and design philosophy are proposed and evaluated for adopting the STT-MRAM technology as highly reliable, energy efficient and fast memory. For this purpose, a novel cross-layer framework from the cell-level all the way up to the system- and application-level has been developed. In these framework, the reliability issues are modeled accurately with appropriate fault models at different abstraction levels in order to analyze the overall failure rates of the entire memory and its Mean Time To Failure (MTTF) along with considering the temperature and process variation effects. Design-time, compile-time and run-time solutions have been provided to address the challenges associated with STT-MRAM. The effectiveness of the proposed solutions is demonstrated in extensive experiments that show significant improvements in comparison to state-of-the-art solutions, i.e. lower-power, higher-performance and more reliable STT-MRAM design
Domain walls in spin-valve nanotracks: characterisation and applications
Magnetic systems based on the manipulation of domain walls (DWs) in nanometre-scaled tracks have been shown to store data at high density, perform complex logic operations, and even mechanically manipulate magnetic beads. The magnetic nano-track has also been an indispensable model system to study fundamental magnetic and
magneto-electronic phenomena, such as field induced DW propagation, spin-transfer
torque, and other micromagnetic properties. Its value to fundamental research and the
breath of potentially useful applications have made this class of systems the focus of
wide research in the area of nanomagnetism and spintronics.
This thesis focuses on DW manipulation and DW-based devices in spin-valve
nanotracks. The spin-valve is a metallic multi-layered spintronic structure, wherein the
electrical resistance varies greatly with the magnetisation of its layers. In comparison to
monolayer tracks, the spin-valve track enables more sensitive and versatile
measurements, as well as demonstrating electronic output of DW-based devices, an
achievement of crucial interest to technological applications. However, these multi-layered tracks introduce new, potentially disruptive magnetic interactions, as well as
fabrication challenges.
In this thesis, the DW propagation in spin-valve nanotracks of different compositions
was studied, and a system with DW propagation properties comparable to the state-of-the-art in monolayer tracks was demonstrated, down to an unprecedented lateral size
of 33nm.
Several DW logic devices of variable complexity were demonstrated and studied,
namely a turn-counting DW spiral, a DW gate, multiple DW logic NOT gates, and a DW-DW interactor. It was found that, where the comparison was possible, the overall
magnetic behaviour of these devices was analogous to that of monolayer structures,
and the device performance, as defined by the range of field wherein they function
desirably, was found to be comparable, albeit inferior, to that of their monolayer
counterparts. The interaction between DWs in adjacent tracks was studied and new
phenomena were observed and characterised, such as DW depinning induced by a
static or travelling adjacent DW.
The contribution of different physical mechanisms to electrical current induced
depinning were quantified, and it was found that the Oersted field, typically negligible
in monolayer tracks, was responsible for large variations in depinning field in SV tracks,
and that the strength of spin-transfer effect was similar in magnitude to that reported
in monolayer tracks. Finally, current induced ferromagnetic resonance was measured,
and the domain uniform resonant mode was observed, in very good agreement to
Kittel theory and simulations
Superconductors at the Nanoscale
By covering theory, design, and fabrication of nanostructured superconducting materials, this monograph is an invaluable resource for research and development. Examples are energy saving solutions, healthcare, and communication technologies. Key ingredients are nanopatterned materials which help to improve the superconducting critical parameters and performance of superconducting devices, and lead to novel functionalities. Contents Tutorial on nanostructured superconductors Imaging vortices in superconductors: from the atomic scale to macroscopic distances Probing vortex dynamics on a single vortex level by scanning ac-susceptibility microscopy STM studies of vortex cores in strongly confined nanoscale superconductors Type-1.5 superconductivity Direct visualization of vortex patterns in superconductors with competing vortex-vortex interactions Vortex dynamics in nanofabricated chemical solution deposition high-temperature superconducting films Artificial pinning sites and their applications Vortices at microwave frequencies Physics and operation of superconducting single-photon devices Josephson and charging effect in mesoscopic superconducting devices NanoSQUIDs: Basics & recent advances intrinsic Josephson junction stacks as emitters of terahertz radiation| Interference phenomena in superconductor-ferromagnet hybrids Spin-orbit interactions, spin currents, and magnetization dynamics in superconductor/ferromagnet hybrids Superconductor/ferromagnet hybrid