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The effect of strain on electronic transport properties in perovskite manganite and ferrite films
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The effect of strain on electronic transport properties in perovskite manganite and ferrite films

Andrew Gabriel Cieri
Master of Science (M.S.), Drexel University
07 Jun 2016
DOI:
https://doi.org/10.17918/etd-6916
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Abstract

Perovskite--Oxides Materials Science Thin Films
In the modern world, the ubiquitous nature of electronic devices and computer driven advancements cannot be overstated. In the last several decades, the increase in processing speed and power of these devices has been tied to the ability of the industry to miniaturize silicon transistors following Moore's Law. The current silicon based technology is approaching the fundamental limit and therefore further advancement might not be possible without development of another material. Transition metal perovskite oxides are a class of materials that could fulfill this need. However, before perovskite oxides can be deployed in commercial electronic devices, a deeper understanding of their electronic behavior is needed. In this thesis, electron transport properties, including carrier mobility, are investigated as a function of epitaxial strain in manganite and ferrite oxide thin films. La_[0.7]Sr_[0.3]MnO₃ (LSMO), La_[0.7]Sr_[0.3]FeO₃ (LSFO) and La_[0.7]Ca_[0.3]MnO₃ (LCMO) were grown on SrTiO₃ (STO), (LaAlO₃)_[0.3](Sr₂AlTaO₆)_[0.7] (LSAT), LaAlO₃ (LAO), SrLaAlO₄ (SLAO), and GdScO₃ (GSO) substrates. The different lattice parameters of the various substrates introduce strain into the films which alters their physical and electronic structure. The films are etched into a Hall bar pattern in order to conduct resistivity and Hall Effect measurements. The Hall Effect is used to calculate carrier concentration, which along with the resistivity produces mobility values for each film. The results show that the induced strain can drastically change the electronic properties by creating insulating or conductive behavior and even altering magnetic transition temperatures for films of the same stoichiometric ratio. LSMO films on STO and LSAT are conductive, while those on SLAO and LAO are insulating. In LCMO, the magnetic transition temperature occurs at 240 K on LSAT, but at 150 K in the STO film. Films with larger strain percentages, such as those on LAO, become insulating at all temperatures. The magnitude of the anomalous Hall Effect and magnetoresistance is larger in the LCMO films compared to the LSMO films. Mobility is also shown to change based on the varied strain state of the film. The mobility of the LSMO film on STO is larger than the LSMO film on LSAT, demonstrating that the carrier mobility in LSMO is dependent on strain type not just strain magnitude.

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