Origin of Magnetic Relaxation Barriers in a Family of Cobalt(II)-Radical Single-Chain Magnets: Density Functional Theory and Ab Initio Calculations.

Density functional theory (DFT) and ab initio calculations were performed to probe the origin of the magnetic relaxation barriers for two finite single-chain magnets (SCMs) featuring a one-dimension chain, Co(hfac)2(R-NapNIT) (R-NapNIT = 2-(2'-(R-)naphthyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, R = MeO (1) or EtO (2)). Our calculations show that the strong intrachain CoII-CoII exchange coupling interactions transmitted by radicals can contribute much more than ionic anisotropy to the height of the reversal barrier of magnetization for the single-chain magnets (SCMs) with |2E| < |4J/3|. In addition, the anisotropic energy barrier ΔA decreases with the decrease of |2E/J| ratio and finally vanishes in the limit of broad domain walls (|2E| < < |4 J/3|). Therefore, the total magnetic relaxation energy barriers of two SCMs mostly originate from the correlation energy barrier Δξ deriving from the indirect ferromagnetic interaction between CoII-CoII transmitted by the strong CoII-radical antiferromagnetic interactions.