Interface engineered functional oxides for future device technology

It is today possible to tailor properties by atomic control of interfaces, central to develop tomorrows environmental friendly electronics. Research on interface properties has been in focus for 70 years, and such research is today central to device technology. Focus is now on perovskite oxides. There is especially focus on how electric conductivity and magnetic properties can be engineered at interfaces, properties highly interesting for electronic applications ? interfaces are now the land of possibilities. We have in this project investigated how structural symmetry at interfaces can be used to establish robust materials for energy efficient device technology. We have especially looked at how structural and physical miss-match across an interface affects the interface properties. Magnetic materials are promising for future device technology, and we have focused on how interface magnetism can be controlled. Important results include how the thickness of the different magnetic layers affects the magnetic domain structure. We have especially shown that for antiferromagnetic/ferromagnetic thin layers it is the antiferromagnetic layer that controls the domain structure of the ferromagnetic layer. This is important for future spintronic applications, and help to elude how such materials can be used in future device technology. The main finding in this project is that 111-oriented interfaces can have large structural reconstructions. We have theoretically shown how lattice vibrations can couple between the different layers, a tool to optimize new structural phases with given properties. We have developed rational design rules to how (111)-strain affects the phonon response, and demonstrated that structural factors, a steric effect, and nominal valence is important for the response. This opens to consider the effect of oxygen rotations at interfaces, and understand how ferroic properties is affected. This methodology, together with the most central result of the project that interfaces between 111-oriented LSMO and LFO exhibit a new magnetic phase, robust and stemming from a correlation between structural symmetry effects and a modulation of electronic correlation strength, opens new possibilities to develop rules for rational design of oxide interfaces.

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There is a continuous development and downscaling of device technology, and the possibility to include novel architectures can enable energy efficient device technology at the same time as the functionality can increase. Systems with multiple order parame ters offers an important avenue towards future digital/electronic devices. At the center for such systems is to develop a thorough understanding and control of the interface between materials with different order parameters. We will rely on recent advan ces in our lab to control the surfaces of thin films with different crystalline orientations, and control the degree of distortion in magnetic oxides. These advancements enable systematic studies of the effect of symmetry mismatch at interfaces; this sinc e it has been shown that such mismatch can induce novel phases at the interface. To this extent we will investigate two complementary model systems, ferroelectric/ferromagnetic and antiferromagnetic/ferromagnetic multiferroic thin films, to study the in terplay between ferroic order at epitaxial interfaces. We will focus on structural symmetry effects at the interface, important to understand and control since there is a strong structure-property relationship in these materials. We will also investigate if the domain structure of one of the layers influence/can be used to control the other layers domain structure. The thin film materials we will primarily use are: ferromagnetic (La,Sr)MnO3, antiferromagnetic LaFeO3, and ferroelectric BaTiO3. Pulsed laser deposition will be used to synthesize the epitaxial heterostructures. To reach our goals within the project we will combine the PI's expertise in epitaxial thin film synthesis, nanostructuring, piezoelectric microscopy and magnetic spectroscopy/imaging using synchrotron radiation sources.