Giant Ferrimagnetism and Polarization in a Mixed Metal Perovskite Metal-Organic Framework

Perovskite metal-organic frameworks (MOFs) have recently emerged as potential candidates for multiferroicity. However, the compounds synthesized so far possess only weak ferromagnetism and low polarization. Additionally, the very low magnetic transition temperatures ($T_c$) also pose a challenge to the application of the materials. We have computationally designed a mixed metal perovskite MOF -[C(NH2)3][(Cu0.5Mn0.5)(HCOO)3]- that is predicted to have magnetization two orders of magnitude larger than its parent ([C(NH2)3][Cu(HCOO)3]), a significantly larger polarization (9.9 {\mu}C/cm2), and an enhanced $T_c$ of up to 56 K, unprecedented in perovskite MOFs. A detailed study of the magnetic interactions revealed a novel mechanism leading to the large moments as well as the increase in the $T_c$. Mixing a non-Jahn-Teller ion (Mn$^{2+}$) into a Jahn-Teller host (Cu$^{2+}$) leads to competing lattice distortions which are possibly responsible for the enhanced polarization. The MOF is thermodynamically stable as evidenced by the computed enthalpy of formation, and can likely be synthesized. Our work represents a first step towards rational design of multiferroic perovskite MOFs through the largely unexlpored mixed metal approach.