Rational design of 2D organic magnets with giant magnetic anisotropy based on two-coordinate 5d transition metals

Abstract

As a new class of single-molecule magnets, two-coordinate complexes of open-shell transition metals are comparatively rare and have attracted interest due to their high degree of coordinative unsaturation. However, the dynamic distortion associated with the low coordination number of the metal center hinders the applications of high-density information storage, quantum computing, and spintronics. Here, we propose a series of stable 2D metal-organic frameworks constructed by ideal (1, 3, 5)-benzenetricarbonitrile (TCB) molecules and 5d transition metals (Hf, Ta, W, Re, Os, and Ir) with a highly symmetrical ligand field and rigid π conjugated framework. Among them, TCB-Re exhibits intrinsic ferromagnetic ordering with a considerably large magnetic anisotropic energy (MAE) of 19 meV/atom and high Curie temperature (TC) of 613 K. Under biaxial strain, diverse magnetic states (such as ferromagnetic, paramagnetic, and antiferromagnetic states) can be achieved in TCB-Re by the complicated competition between the in-plane d-px/y-d and out-of-plane d-pz-d superexchange interactions. At a small compressive strain of 0.5%, the MAE for perpendicular magnetization increases substantially to 120 meV/atom; meanwhile, the magnetization and TC above room temperature are well retained. Our results not only extend two-coordinate transition metal complexes to continuous 2D organic magnets but also demonstrate an effective method of strain engineering for manipulating the spin state and MAE.