Open AccessHigh temperature ferromagnetism in π-conjugated two-dimensional metal–organic frameworks
Author(s) -
Wenbin Li,
Lei Sun,
Jingshan Qi,
Pablo JarilloHerrero,
Mircea Dincă,
Li Ju
Publication year - 2017
Publication title -
chemical science
Language(s) - Uncategorized
Resource type - Journals
SCImago Journal Rank - 3.687
H-Index - 172
eISSN - 2041-6539
pISSN - 2041-6520
DOI - 10.1039/c6sc05080h
Subject(s) - ferromagnetism , metal organic framework , conjugated system , materials science , anisotropy , metal , condensed matter physics , chemical physics , nanotechnology , chemistry , metallurgy , physics , polymer , optics , composite material , adsorption
We use first-principles calculations to show that the square symmetry of two-dimensional (2D) metal-organic frameworks (MOFs) made from octaamino-substituted phthalocyanines and square planar Ni 2+ ions, which enable strong conjugation of π electrons, has a critical impact on the magnetic properties of the lattice. In particular, we predict the unexpected emergence of a rare high-temperature ferromagnetic half-metallic ground state in one case. Among charge neutral MOFs made from (2,3,9,10,16,17,23,24)-octaiminophthalocyanine (OIPc) metallated with divalent first-row transition metal ions (M-OIPc; M = Cr 2+ , Mn 2+ , Fe 2+ , Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ ) and connected through square planar Ni-bisphenylenediimine moieties, NiMn-OIPc exhibits a half-metallic and ferromagnetic ground state with a large exchange energy resulting from the unique strong hybridization between the d/π orbitals of Mn, the Pc ring, and the Ni-bisphenylenediimine nodes. Notably, we show that for NiMn-OIPc there is a considerable difference between the ferromagnetic ordering temperature ( T c ) predicted by a 2D Ising model, which exceeds 600 K, and a T c of 170 K predicted by our more realistic Monte Carlo simulation that includes magnetic anisotropy. Critically, our simulations adopt two spin models that incorporate magnetic anisotropy in the form of exchange anisotropy and single-ion anisotropy. We further show that in the bulk, 2D layers of NiMn-OIPc adopt a slipped-parallel stacking configuration, and exhibit interlayer magnetic coupling that is sensitive to the relative in-plane displacement between adjacent layers. These results highlight the critical role of magnetic anisotropy in modeling the properties of 2D magnetic systems. More generally, it demonstrates that strong hybridization between open-shell ions and delocalized aromatic π systems with appropriate symmetry, combined with large magnetic anisotropy, will be an effective design strategy to realize ferromagnetic 2D MOFs with high T c .