|Title: ||Magnetism and spin transport studies on indium tin oxide|
|Authors: ||Hakimi, Ali Moraad Heydar|
|Supervisors: ||Blamire, Mark Gifford|
|Issue Date: ||12-Jul-2011|
|Abstract: ||This dissertation reports on a detailed systematic study of the investigation into
using Indium Oxide based materials in next generation spin-transport electronic applications.
Initial studies focused on the optimisation of the electrical properties of Indium
Oxide (In2O3) and Tin(Sn)-doped Indium Oxide (ITO) thin films grown using DC
magnetron sputtering. The manipulation of various deposition parameters allowed the
electrical properties to be tuned effectively.
With the desire to create multi-functional spintronic devices, a dilute magnetic oxide
system is developed where the In2O3 and ITO matrices are doped with low levels
of transition metals, in particular, Co. Using a number of characterisation techniques,
the origins of the magnetic response in these thin films is explored in great detail. In
particular, powerful probes such as x-ray and optical magnetic circular dichroism are
utilised. The major finding from these investigations is that the magnetism does not
necessarily emanate from the Co dopants alone. In fact, Co dopants give a strictly
paramagnetic response, suggesting that the magnetism observed may be a result of
polarised electrons in localised donor states in the In2O3 and ITO hosts. Therefore, we
believe that the origins of magnetism in these films is related to a hybridisation and
charge transfer of electrons from a broad donor/defect-derived impurity band to a band
of unoccupied 3d states at the Fermi level. The emergence of a very weak magnetic
signal in pure ITO raises further questions as to the true origins of the ferromagnetic
behaviour and supports a defect-related mechanism.
To explore the suitability of ITO for a future in spintronics further, the performance
of some metal ferromagnet/oxide multilayered structures was investigated. The
investigations revealed a significant contribution to both the magnetic and magnetotransport
properties from a superparamagnetic component giving some insight into the
importance of the quality of interfaces between the metal ferromagnet/oxide layers and
Using a three-dimensional focused-ion beam etching technique to fabricate submicron
spin-valve devices with ITO spacer layers, current-perpendicular-to-plane magnetoresistance
measurements were carried out to estimate the spin diffusion length of
ITO at room temperature. In conjunction with a simplified Valet-Fert model, a spin
asymmetry ratio for Co of 0.55 and spin diffusion length of 6±1 nm in semiconducting
ITO at room temperature was estimated. These findings imply that spin information
can be conserved and transported through In2O3 and ITO even up to and beyond room
|Appears in Collections:||Theses - Materials Science and Metallurgy|
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