Document Type

Dissertation

Date of Award

8-31-2009

Degree Name

Doctor of Philosophy in Applied Physics - (Ph.D.)

Department

Federated Physics Department

First Advisor

Trevor Tyson

Second Advisor

N. M. Ravindra

Third Advisor

Tao Zhou

Fourth Advisor

Zhenxian Liu

Fifth Advisor

Weida Wu

Sixth Advisor

Ken Keunhyuk Ahn

Abstract

Rare-earth Manganese Oxides (RMnO3) exhibit two distinct structural phases: the orthorhombic structure and the hexagonal structure. The doped orthorhombic phase exhibits a metal to insulator transition, charge ordering and a strong response of electron transport properties to magnetic fields (colossal magneto-resistance). At low temperatures, this system may also exhibit a finite polarization which couples to external magnetic fields. The hexagonal phase is known to have a large spontaneous polarization at high temperatures which couples to the low temperature magnetic order. These materials are important from the basic point of view of understanding strong electronic correlations and spin-lattice coupling. From, a practical perspective, they hold promise to produce sensors and storage devices with extremely high sensitivity and high density. However, a detailed understanding of their properties is needed.

In this work, optical, transport and structural measurements, as a function of pressure and temperature, are conducted to explore the physical properties of these materials. Synchrotron based x-ray diffraction and infrared measurements, Raman measurement, laboratory based transport measurements and neutron scattering measurements were conducted on bulk polycrystalline, thin film and single crystal samples. The electronic, structural and magnetic properties are studied in detail. The results will be used to refine theoretical models of these materials.

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