An Air-Stable and Exfoliable Ferromagnetic Two-Dimensional Perovskite, (Phenethylammonium)₂CrCl₄

Synthesis and structural characterization of the 2D hybrid-perovskite ferromagnet (PEA)2CrCl4 are reported (PEA = phenethylammonium). Single-crystal X-ray diffraction shows isolated inorganic sheets separated by bilayers of the bulky PEA cation. The inorganic sheets consist of networked [CrCl6]4– octahedra with ordered in-plane Jahn–Teller distortions. The PEA cations impart air stability to these otherwise highly hygroscopic and oxidatively unstable compounds. (PEA)2CrCl4 is ferromagnetically ordered with TC = 44 K and shows rich temperature-dependent absorption in the visible region that reflects coupling of Cr2+ optical spin-flip transitions to 2D magnons. The van der Waals lattice structure has allowed mechanical exfoliation of monolayers with micrometer lateral dimensions, and air stability is largely retained. These attributes make (PEA)2CrCl4 an attractive platform for development of 2D perovskite chemistry that links structure, magnetism, and magneto-optics, including at the monolayer limit.