The Effect of Strain on the Phase Separation and Magnetoelectric Coupling in Manganites

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NON-TECHNICAL ABSTRACTMultiferroics are compounds which can be simultaneously magnetized (areferromagnetic) and electrically charged (are ferroelectric). Suchcompounds hold promise for applications in devices and lead tounprecedented data-storage capacity. However, the underlying mechanismwhich leads to such unique properties is poorly understood and needs to beresolved before practical devices can be fabricated. This individualinvestigator award supports the study of a family of multiferroicmanganese oxide compounds known as manganites. The properties ofmanganites are intimately linked to their crystal structure. The theme ofthis project is to quantify the role played by crystal structure inmultiferroic manganites and suggest methods to design materials bettersuited for device applications. High quality manganite thin films will begrown using laser ablation. These thin films' response to strain (changein the crystal structure) will be studied by measuring the change in theirelectrical resistance and magnetism. The microscopic effect of strain willbe studied using techniques such as a microscope capable of mapping thelocal magnetism of the material. Since the research and training programincludes both sample preparation and measurement, this award will helptrain undergraduate and graduate students in various aspects of condensedmatter physics research and give them a broad based experience, which willenhance their future career options in the industry or academe.TECHNICAL ABSTRACTPerovskite manganese oxides (manganites) display unique properties such asmicrometer scale phase separation and multiferroism, which are intimatelylinked to their crystal structure. Hence, the electrical and magneticproperties of manganites are sensitive to strain. This individualinvestigator award supports an experimental program to directly measurethe effect of strain on the properties of manganites and by comparing theresults to the predictions of theoretical models, determine the origin ofphase separation and multiferroism in manganites. The experimental resultsare also expected to reveal methods of enhancing the magnetoelectriccoupling in multiferroic manganites and controlling the nanoscaleproperties of phase separated manganites. High quality manganite thinfilms will be grown using pulsed laser deposition. The thin films willthen be subjected to direct external stress using a three pointbeam-bending apparatus to induce uniaxial strain in the material. Using acomplementary suite of local and bulk measurement techniques such asmagnetotransport, magnetization, scanning probe microscopy, and neutronreflectometry, the phase diagram of the thin films will be mapped as afunction of strain, magnetic field, electric field, and temperature. Sincethe research and training program includes both sample preparation andmeasurement, undergraduate and graduate students will be able to learnabout a wide variety of materials and experimental techniques, which willprepare them for academic and industrial careers.