Characterization of magnetic ordering in porphyrin-based molecular magnets [Mn(R)4TPP][TCNE] (R=OC12H25, F, CN)

The paper deals with certain charge transfer molecular magnets built of chains with [MnTPP] cations bound to [TCNE] anions (TPP = tetraphenylporphyrin, TCNE = tetracyanoethylene). Magnetic moments, coming from Mn-III d orbitals and from anion p orbitals, are strongly coupled in the chain. Three modifications, [MnR4TPP] [TCNE] x solvent with R ( = OC12H25, F, CN) groups substituted at the periphery of the porphyrin disc, are investigated by means of AC susceptibility and DC magnetization measurements. The temperature T-c, of the transition from the short-range one-dimensional ferrimagnetic order to the cooperative low-temperature state, is equal to 22, 27 and 20 K for R = OC12H25, F and CN, respectively. For the first compound the transition is especially sharp. Below T-c, the compounds show both ferromagnetic (FM) and spin-glass (SG) properties, the latter ones caused by random anisotropy due to the solvent. Competition between FM and SG ordering results in "reentrance" to the SG state at the glass temperature T-g. At T = 4.2 K, compounds with R = OC12H25 and R = F show substantial coercivity and remanant magnetization. For the first sample, the magnetization jump at the virgin curve, identified as the spin flop, is seen at H-j congruent to 4 kOe for 4.2 K. The magnetization process changes dramatically with temperature. (C) 1999 Elsevier Science B.V. All rights reserved.