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Title: Magnetic and electrical properties of transition-metal-doped oxide thin films
Authors: Lam, Ching-yee
Degree: Ph.D.
Issue Date: 2009
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-SrTiO2 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.
Subjects: Hong Kong Polytechnic University -- Dissertations.
Thin films -- Magnetic properties.
Metallic films -- Magnetic properties.
Thin films -- Electric properties.
Metallic films -- Electric properties.
Pages: iv, 276 leaves : ill. (some col.) ; 30 cm.
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