MSE Colloquium - Prof. Chris Leighton
Date: October 25, 2013 from 11:00 am to 12:00 pm EDT
Location: Room 214, S.W. Mudd
Contact: For further information regarding this event, please contact Wesley Hattan by sending email to wjh2121@columbia.edu or by calling 2128547860.
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Chris Leighton
Dept. of Chemical Engineering and Materials Science,
University of Minnesota

Engineering Interface Transport and Magnetism via Defect Control in Complex Oxide Heterostructures

The remarkable functionality and compatibility of complex oxides provides many opportunities for new science and applications in oxide heterostructures. The manganite and cobaltite materials crystallizing in the perovskite structure provide excellent examples, being of interest in solid oxide fuel cells, catalysis, ferroelectric RAM, gas sensing, resistive switching memory, and oxide electronics/spintronics. However, the same delicate balance between phases that provides such diverse functionality also leads to a serious problem: the difficulty of maintaining desired properties close to the interface with other oxides, i.e. "dead layer" formation. Although this problem appears universal, and presents a significant roadblock to heterostructured devices for oxide electronics, there is no consensus as to its origin, or whether it is driven by electronic or chemical effects. In this work, using SrTiO3/La1-xSrxCoO3 as a model system (i.e. a non-magnetic semiconductor / ferromagnetic metal interface), we have determined the fundamental origin of the deterioration in interfacial transport and magnetic properties. The effect is found to be due to nanoscopic magnetic phase separation near the interface, driven by depletion in hole doping due to accumulation of oxygen vacancies. This occurs due to a novel mechanism for accommodation of lattice mismatch based on formation and long-range ordering of oxygen vacancies, thus providing a fundamental link between strain and oxygen vacancy density. With this understood we demonstrate how interfacial magnetic and electronic properties can be controllably fine-tuned by manipulating oxygen vacancy ordering using both heteroepitaxial strain and crystallographic orientation. The result is a massive suppression in dead layer thickness, an important advance for heterostructured oxide devices.

Work supported by DOE and NSF.