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