  Magnetic systems based on the manipulation of domain walls (DWs) in
nano-tracks have been shown to store data at high density, perform complex
logic operations, and mechanically manipulate magnetic beads. The magnetic
track has been a model system to study magnetic and magneto-electronic
phenomena, such as field induced DW propagation and spin-transfer torque. This
thesis focuses on DW manipulation and DW-based devices in spin-valve (SV)
tracks. In comparison to monolayer tracks, the SV track enables more sensitive
and versatile measurements, as well as an electronic output of DW-based
devices, of crucial interest to applications. However, these multi-layered
tracks add new, potentially disruptive magnetic interactions, as well as
fabrication challenges. In this thesis, the DW propagation in SV tracks 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 logic devices were
demonstrated and studied, namely a turn-counting DW spiral, a DW gate, DW logic
NOT gates, and a DW-DW interactor. It was found that the 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 to that of monolayer systems. The interaction
between DWs in adjacent tracks was studied and new phenomena were
characterised, such as DW depinning induced by a static or travelling adjacent
DW. The contribution of different mechanisms to electrical current induced
depinning were quantified, and it was found that the Oersted field, 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 to that
reported in monolayer tracks.
