II.A.1.b.iii.3: Coupling Magnetic and Ferroelectric Phenomena in Designed 2D Thio- and Selenophosphate Crystals

For almost a decade, the majority of research community’s attention has been focused on layered transition metal di-chalcogenide (TMDC) systems. While the typical and obvious variations to their crystal chemical architecture have been explored, these have all been largely constrained to a limited range of compositions and structures. Yet, a quick glance at the periodic table shows the prospects for more complex compositions coupled to cation motifs that can form more functional layered crystal systems with the high potential to exhibit novel properties and phenomena. This interdisciplinary project focuses on fundamental studies of the two-dimensional (2D) metal chalcophosphates of the type M2P2Q6 (M= divalent metal, Q=S, Se) and AMP2Q6 (A=monovalent metals, M=trivalent metal). These materials are semiconductors or Mott insulators, with the selenides having narrower bandgaps than the sulfides. Their great degree of functionality and tunability comes from distinct elements which lend themselves to straightforward chemical manipulation and control. The metal chalcophosphates (MCP) provide either magnetic or ferroelectric behavior, depending on their composition. In the form M2P2Q6, where M is a divalent transition metal ion (Mn, Fe, Co, Ni)), they represent a unique family of layered, anisotropic magnetic insulators or semiconductors. In the form AMP2Q6, where A is a metal (Li, Cu, Ag) and M a post-transition metal (Cr, In, Bi), the resulting class of materials are ferro or antiferroelectric instead of magnetic (e.g., AgBiP2Se6). We plan to grow single crystals of metal chalcophosphates and investigate their magnetic and ferroelectric properties in detail. As a new class of materials we will design them to exhibit both magnetic and ferroelectric order, with coupling of these two order parameters at the atomic level. We seek to identify and study unique combinations of non-linear ferromagnetic and ferroelectric phenomena in the few layer or single layer limits and how they are coupled to each other. We anticipate a new type of 2D magnetoferroelectric materials with unique sets of properties.