Invited Paper TF+EM+MI+MN+OX+PS-MoM1
A Room-Temperature Magnetoelectric Multiferroic made by Thin Film Alchemy

Monday, October 21, 2019, 8:20 am, Room A122-123

Materials that couple strong ferroelectric and ferromagnetic order hold tremendous promise for next-generation memory devices. Meticulous engineering has produced novel ferroelectric and multiferroic materials, although known single-phase multiferroics remain limited by antiferromagnetic or weak ferromagnetic alignments, by a lack of coupling between the order parameters, or by having properties that emerge only well below room temperature. Here we construct single-phase multiferroic materials in which ferroelectricity and strong magnetic ordering are coupled near room temperature. Starting with hexagonal LuFeO₃—a geometric ferroelectric with planar rumpling—we introduce individual monolayers of ferrimagnetic LuFe₂O₄ within the LuFeO₃ matrix, that is, (LuFeO₃)_m/(LuFe₂O₄)₁ superlattices. The rumpling of the LuFeO₃ drives the ferrimagnetic LuFe₂O₄ into a ferroelectric state, reducing the LuFe₂O₄ spin frustration. This increases the magnetic transition temperature to 281K for m=9. Moreover, the ferroelectric order couples to the ferrimagnetism, enabling direct electric-field control of magnetism at 200 kelvin. Further, charged ferroelectric domain walls align at LuFe₂O₄ layers, resulting in charge transfer which increases the magnetic moment. We are currently pursuing higher temperature multiferroics by incorporating cubic spinels with high magnetic ordering temperatures, such as CoFe₂O₄, into the LuFeO₃ matrix. Our results demonstrate a design methodology for creating higher-temperature magnetoelectric multiferroics through epitaxial engineering.