| Summary: | The past few decades have witnessed a race towards developing smaller, faster,
cheaper and ultra high capacity data storage technologies. In particular, this race
has been accelerated due to the emergence of the internet, consumer electronics,
big data, cloud based storage and computing technologies. The enormous increase
in data is paving the path to a data capacity gap wherein more data than can be
stored is generated and existing storage technologies would be unable to bridge this
data gap. A novel approach could be to shift away from current two dimensional
architectures and onto three dimensional architectures wherein data can be stored
vertically aligned on a substrate, thereby decreasing the device footprint. This thesis
explores a data storage concept based on vertically aligned cylindrical magnetic
nanowires which are promising candidates due to their low fabrication cost, lack of
moving parts as well as predicted high operational speed. In the proposed concept,
data is stored in magnetic nanowires in the form of magnetic domains or bits which
can be moved along the nanowire to write/read heads situated at the bottom/top of
the nanowire using spin polarized current.
Cylindrical nanowires generally exhibit a single magnetic domain state i.e. a
single bit, thus for these cylindrical nanowire to exhibit high density data storage, it
is crucial to pack multiple domains within a nanowire. This dissertation
demonstrates that by introducing compositional variation i.e. multiple segments
along the nanowire, using materials with differing values of magnetization such as
cobalt and nickel, it is possible to incorporate multiple domains in a nanowire. Since
the fabrication of cylindrical nanowires is a batch process, examining the properties
of a single nanowire is a challenging task. This dissertation deals with the
fabrication, characterization and manipulation of magnetic domains in individual
nanowires. The various properties of are investigated using electrical
measurements, magnetic microscopy techniques and micromagnetic simulations.
In addition to packing multiple domains in a cylindrical nanowire,
this dissertation reports the current assisted motion of domain walls along
multisegmented Co/Ni nanowires, which is a fundamental step towards achieving a
high density cylindrical nanowire-based data storage device.
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