Magnetism in organic materials

Abstract

Tailoring magnetic interactions of organic solids is currently an area of intense research activity. We show that the quasi-one dimensional anti-ferromagnetic exchange coupling of the well-known organic free radical triphenylverdazyl (TPV) can be increased by a factor of 3 by systematic molecular modifications (i.e. J1d/kB = −16K for 1,3,5,6-tetraphenyl-verdazyl). 1,3,5-tri-6'-(1,3,5-triphenylverdazyl)-benzene as a representative of covalently bound multiradical molecules was analyzed as solid and in solution. The energetic spin-doublet-quartet separation and intermolecular exchange interaction were estimated. Cooperative magnetic behaviour with ordering temperature of about 40K and well-defined hysteresis loops (Hc(5 K) ≈ 40 Oe) has been achieved by the chelation of transition metals (e.g. Mn) in appropriate organic materials. NMR, ESR, static magnetic susceptibility, in part also a.c. susceptibility, specific heat and x-ray structural analysis were used to characterize these new organic magnetic materials.