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Layered Ferromagnetic and Ferrielectric Materials

Michael A. McGuire, MSTD devision, Oak Ridge National Laboratory
Friday, September 30, 2016 - 3:00pm to 4:00pm
PAT C-520

The promise of new phenomena and functionalities is driving research efforts toward designer heterostructures built by stacking layers of multiple materials with complementary properties. The top-down approach to producing the ultra-thin building blocks, mechanical exfoliation of layers from bulk single crystals, provides an exciting opportunity for collaboration among nanoscience researchers who study heterostructured devices and crystal growers who produce and study bulk materials. I will provide an overview of two classes of materials that we have recently grown and studied, transition metal halides and transition metal thiophosphates, which are of interest for this type of research. Both are composed of easily cleavable, van der Waals bonded layers and display ferroic order. After introducing the two material families and describing their crystal chemistry and basic physical properties, I will discuss in some detail ferromagnetism in chromium trihalides and ferrielectricity in copper-based thiophosphates. Chromium trihalides (CrCl3, CrBr3, and CrI3) are Mott insulators that undergo crystallographic phase transitions and order magnetically at low temperature. Layered thiophosphates (e.g. CuInP2S6) include antiferroelectric and ferrielectric materials with transition temperatures that can exceed room temperature, and in which we have recently demonstrated in-plane heterostructure formation via chemical phase separation.​