A Route to Two-Dimensional Room-Temperature Organometallic Multiferroics: The Marriage of d–p Spin Coupling and Structural Inversion Symmetry Breaking

Two-dimensional (2D) room-temperature multiferroic materials are highly desirable but still very limited. Herein, we propose a potential strategy to obtain such materials in 2D metal–organic frameworks (MOFs) by utilizing the d–p direct spin coupling in conjunction with center-symmetry-breaking six-membered heterocyclic rings. Based on this strategy, a screening of 128 2D MOFs results in the identification of three multiferroics, that is, Cr(1,2-oxazine) 2, Cr(1,2,4-triazine) 2, and Cr(1,2,3,4-trazine) 2, simultaneously exhibiting room-temperature ferrimagnetism and ferroelectricity/antiferroelectricity. The room-temperature ferrimagnetic order (306–495 K) in these MOFs originates from the strong d–p direct magnetic exchange interaction between Cr cations and ligand anions. Specifically, Cr(1,2-oxazine) 2 exhibits ferroelectric behavior with an out-of-plane polarization of 4.24 pC/m, whereas the other two manifest antiferroelectric characteristics. Notably, all three materials present suitable polarization switching barriers (0.18–0.31 eV). Furthermore, these MOFs are all bipolar magnetic semiconductors with moderate band gaps, in which the spin direction of carriers can be manipulated by electrical gating.