Research
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IRG5, Strain-Enabled Multiferroics
Leader : Venkat GopalanIRG faculty and seed faculty: Long-Qing Chen, Venkat Gopalan, Xiaoqing Pan, Karin Rabe, Ramamoorthy Ramesh, Peter Schiffer, Darrell Schlom, Nicola Spaldin, and Xiaoxing Xi.
The theme of IRG5 is to create and investigate the properties of new multiferroics, whose very existence (as multiferroics) is made possible by strain. Traditionally the search for new multiferroics involves identifying unstrained phases that exist within composition space. Adding strain vastly increases the dimensional space available to adjust the properties of multiferroics.
Recent highlights:
New discoveries in this project include strain-enabled ferroelectricity in BaTiO3/SrTiO3 super-lattices, multiferroicity in strained-SrTiO3, the new multiferroic PbVO3, and electrical control of magnetism in multiferroic nanocomposites. Predictions (Rabe, Spaldin, Chen) of the effect of composition and biaxial strain on multiferroic properties are used to target specific materials and strain states. These predictions, including dimensional constraints, are then implemented in epitaxial films (Schlom). The performance is measured over a range of length and time scales (Gopalan, Pan, Ramesh, Schiffer, Xi, and collaborators at national laboratories) and compared to theory to provide understanding, improved abilities to customize multiferroics, and dramatically enhanced multiferroic properties.
Using oxide MBE growth methods, we have demonstrated that SrTiO3, which is neither ferroelectric nor multiferroic in bulk form, can be strained in thin film form to be a multiferroic, exhibiting independent order parameters and phase transitions to ferroelectric and ferroelastic phases. In this study, ultraviolet Raman spectroscopy was shown to be capable of detecting ferroelectricity in one-unit-cell-thick materials.