Two-Dimensional Multifunctional Metal–Organic Frameworks with Simultaneous Ferro-/Ferrimagnetism and Vertical Ferroelectricity

Exploring 2D multifunctional materials with intrinsic ferro-/ferrimagnetism and vertical ferroelectricity is a highly desirable but challenging task. Here, motivated by the recently synthesized organometallic frameworks K3Fe2[PcFeO8], we propose to realize such materials in a series of 2D K3M2[PcMO8] (M = Cr–Co) nanosheets. First-principles calculations suggest 2D K3Cr2[PcCrO8] as a ferromagnetic half metal with a Curie temperature of 140 K, whereas others (M = Mn, Fe, and Co) are all ferrimagnetic semiconductors with the Curie temperatures between 66 and 150 K. Moreover, the structural distortion due to the out-of-plane K+ counterions leads to a significant vertical electric polarization. The estimated intensity of polarization for K3Fe2[PcFeO8] is 143 pC/m, with the ferroelectric phase-transition barrier being 0.38 eV per formula. This work highlights the potential of 2D organometallic frameworks such as K3M2[PcMO8] as a versatile platform for designing multifunctional materials with simultaneous ferro-/ferrimagnetism and vertical ferroelectricity.