<p>Functional oxide-based thin films
have attracted much attention owing to their broad applications in modern
society. The multifunction tuning in oxide thin films is critical for obtaining
enhanced properties. In this dissertation, four new nanocomposite thin film
systems with highly textured growth have been fabricated by pulsed laser
deposition technique. The functionalities including ferromagnetism,
ferroelectricity, multiferroism, magnetoelectric coupling, low-field
magnetoresistance, transmittance, optical bandgap and dielectric constants have
been demonstrated. Besides, the tunability of the functionalities have been
studied via different approaches.</p>
<p>First, varies deposition
frequencies have been used in vertically aligned nanocomposite BaTiO<sub>3</sub>:YMnO<sub>3</sub>
(BTO:YMO) and BaTiO<sub>3</sub>:La<sub>0.7</sub>Sr<sub>0.3</sub>Mn<sub>3
</sub>(BTO:LSMO) thin films. In both systems, the strain coupling effect
between the phases are affected by the density of grain boundaries. Increasing
deposition frequency generates thinner columns in BTO:YMO thin films, which
enhances the anisotropic ferromagnetic response in the thin films. In contrast,
the columns in BTO:LSMO thin films become discontinuous as the deposition
frequency increases, leading to the diminished anisotropic ferromagnetic
response. Coupling with the ferroelectricity in BTO, the room temperature
multiferroic properties have been obtained in these two systems.</p>
<p> Second, the
impact of the film composition has been demonstrated in La<sub>0.7</sub>Ca<sub>0.3</sub>MnO<sub>3</sub>
(LCMO):CeO<sub>2 </sub>thin film system, which has an insulating CeO<sub>2 </sub>in
ferromagnetic conducting LCMO matrix structure. As the atomic percentage of the
CeO<sub>2 </sub>increases, enhanced low-field magnetoresistance and increased
metal-to-insulator transition temperature are observed. The thin films also
show enhanced anisotropic ferromagnetic response comparing with the pure LCMO
film.</p>
<p> Third, the
transition metal element in Bi<sub>3</sub>MoM<sub>T</sub>O<sub>9 </sub>(M<sub>T</sub>,
transition metals of Mn, Fe, Co and Ni) thin films have been varied. The thin
films have a multilayered structure with M<sub>T</sub>-rich pillar-like domains
embedded in Mo-rich matrix structure. The anisotropic magnetic easy axis and
optical properties have been demonstrated. By the element variation, the
optical bandgaps, dielectric constants as well as anisotropic ferromagnetic
properties have been achieved. </p>
<p> The studies
in this dissertation demonstrate several examples of tuning the
multifunctionalities in oxide-based nanocomposite thin films. These enhanced
properties can broaden the applications of functional oxides for advanced
nanoscale devices.</p><br>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/11328515 |
| Date | 06 December 2019 |
| Creators | Xingyao Gao (8088647) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/TUNABLE_MULTIFUNCTIONALITIES_ACHIEVED_IN_OXIDE-BASED_NANOCOMPOSITE_THIN_FILMS/11328515 |
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