Synthesis and Spectroscopy of Ferromagnetic 2D Chromium-Halide Perovskites, A₂CrX₄

This talk will describe our group's recent progress in the development of new forms of chromium-based two-dimensional magnetic perovskites, A₂CrX₄ (A = monovalent cation, X = halide). Most prior work on A₂CrX₄ compounds was performed before the relatively recent renaissance of hybrid lead-based 2D perovskites, motivating further investigation into their chemistry and properties. We have synthesized large crystals of the new hybrid compound, (PEA)₂CrCl₄, via an antisolvent vapor-diffusion method. The structure of (PEA)₂CrCl₄ shows sheets of distorted [CrCl₆]^4- octahedra spaced by PEA bilayers with a van der Waals gap between them, and we demonstrate that these crystals can be mechanically exfoliated down to single monolayers with micron lateral dimensions. In stark contrast with other known A₂CrCl₄ compounds, which are extremely hygroscopic and unstable toward oxidation, (PEA)₂CrCl₄ is found to be stable in air for many days, even after exfoliation. Magnetic measurements show in-plane ferromagnetic ordering, and electronic absorption measurements allow 2D spin correlations at zero field to be monitored via the evolution of Cr²⁺ spin-flip excitations. These and related findings will be presented.