Strain Controlled Functionalities in Lightly Doped Manganite Perovskite Epitaxial Thin Films Grown by Pulsed Laser Deposition
Author: Richard Teboh Mbatang
Publisher:
Published: 2018
Total Pages: 188
ISBN-13:
DOWNLOAD EBOOKFunctional Oxides have been widely studied in the last decades because of their fascinating properties as ferromagnetism, ferroelectricity, superconductivity and multiferroicity. The widely studied complex oxides are the perovskite and the hexagonal oxides. Intriguing phenomena have been observed in epitaxial thin films of manganite perovskites, which greatly differed from those of bulk material. Some of the interesting properties of lightly doped manganite oxide thin films, especially La0.9Sr0.1MnO3 thin films, are an enhanced magnetoresistance (MR) and temperature coefficient of resistance (TCR). The physical properties of these films are related to the effects that occur at the interface. Some of these interfacial effects includes defect formation, charge transfer, exchange coupling, strain, interfacial reconstruction and cation intermixing. The fast development of new characterization techniques have made the study of interfacial effects easy. Fabrication techniques such as Pulsed Laser Deposition (PLD) have been employed to produce interfaces with great atomic precision. Selecting materials with the right lattice mismatch and optimization of the growth conditions as laser repetition rate, temperature, oxygen pressure, substrate-target distance and laser energy are crucial in growth of epitaxial thin films for functional device application. In addition to these, selecting the right proposition of the various phase is important in achieving the right microstructure for composite films. The main focus of this dissertation is to investigate the relationship between structure and magneto-transport properties in lightly doped manganite perovskite thin films with the concentration on 10% strontium doped lathanum manganese oxide, La0.9Sr0.1MnO3 (LSMO) grown by Pulsed Laser Deposition (PLD). We grew films of different thicknesses (15 nm, 30 nm, 75 nm) and on different substrates ((001) LaAlO3 (LAO, (001) SrLaGaO4 (LSGO), (110), GdScO3 (DSO) and (110) GaScO3). We found that thinner films show highly enhanced magnetic and transport properties while thicker films exhibit low transport and magnetic properties due to strain relaxation. We also observed that compressive strain enhanced magnetic (saturation magnetization, Curie temperature (Tc)) and transport properties (metal-insulating transition (MIT), magnetoresistance (MR), temperature coefficient of resistance (TCR)). The enhancement of magnetic and transport properties were attributed to the suppression of Jahn-Teller distortion, electron-phonon coupling and the enhancement of double exchange coupling. In summary, strain can be used to tune the physical properties of expitaxial thin films for technological applications.