Please use this identifier to cite or link to this item: http://hdl.handle.net/10397/2978
Title: Magnetic and electrical properties of transition-metal-doped oxide thin films
Authors: Lam, Ching-yee
Subjects: Hong Kong Polytechnic University -- Dissertations
Thin films -- Magnetic properties.
Metallic films -- Magnetic properties
Thin films -- Electric properties
Metallic films -- Electric properties
Issue Date: 2009
Publisher: The Hong Kong Polytechnic University
Abstract: In this research programme, the electrical and magnetic properties of PLD and room temperature grown TM-doped TiO₂ and TM-doped CuxO thin films have been investigated. We used Co and Fe as the TM dopants for the TiO₂ based films. Mn was however used to dope the CuxO materials systems. Among the various electrical properties, resistive switching of transition-metal oxide thin films and electrical rectifying property of an all-oxide p-n diode have been studied. The resistive switching of anatase phase TM-doped TiO₂ has been determined using two top-down configurations of Ag/TM-doped TiO₂/Pt and In/TM-doped TiO₂/TiN. Despite the fact that same transition-metal oxide was used, the switching characteristics of these two configurations were significantly different. For example, both the unipolar and bipolar switching were observed in pure TiO₂ films. For the In/TiO₂/TiN arrangement, enhancement is observed in Fe-doping. Doping Co, however, appears to reduce the switching ratio. Heterostructures of Ag/TiO₂/Pt have also been deposited on flexible PET substrates at room temperature by PLD. These oxide films on flexible substrate not only show resistive switching, but produce an average switching ratio as high as over 6 orders of magnitude. The resistive switching in In/CuxO/Pt and In/Mn-doped CuxO/Pt films have also been demonstrated in the present study. Our results indicate clearly that the switching stability of the In/CuxO/Pt systems is improved by the Mn-doping. The magnetic properties of these two oxide material systems have also been evaluated. Our ultimate goal is to produce a ferromagnetic all-oxide p-n junction diode. We obtained room-temperature ferromagnetism in the epitaxially grown anatase n-type Co-doped TiO₂ and possible p-type Fe-doped TiO₂ thin films. At the same time, the 3.7 at.% Mn-doped Cu₂O epitaxial films have been prepared. They are p-type conducting and have been properly utilized to form good rectifying all-oxide heterojunction with the n-type Nb-SrTiO₃ substrates. The p-type Mn-doped Cu₂O films that we have made so far, although exhibit ferromagnetism at low temperatures <50K, do not reveal any room temperature ferromagnetic characteristics. Indeed, phase segregation of Mn₃O₄ is accountable for the low temperature ferromagnetism. It is believed that room temperature ferromagnetism in Mn-doped Cu₂O is still possible if the Mn-doping level is kept well below the solubility limit of Mn in Cu₂O. The experimental investigations carried out so far in the present research do provide strong indication and support for realization of spintronic heterojunctions based on n-type Co-TiO₂/p-type Mn-doped Cu₂O.
Description: iv, 276 leaves : ill. (some col.) ; 30 cm.
PolyU Library Call No.: [THS] LG51 .H577P AP 2009 Lam
Rights: All rights reserved.
Type: Thesis
URI: http://hdl.handle.net/10397/2978
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