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

The paper deals with certain charge transfer molecular magnets built of cha ins with [MnTPP] cations bound to [TCNE] anions (TPP = tetraphenylporphyrin , TCNE = tetracyanoethylene). Magnetic moments, coming from Mn-III d orbita ls and from anion p orbitals, are strongly coupled in the chain. Three modi fications, [MnR4TPP] [TCNE] x solvent with R ( = OC12H25, F, CN) groups sub stituted 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 orde r 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 anisotrop y due to the solvent. Competition between FM and SG ordering results in "re entrance" to the SG state at the glass temperature T-g. At T = 4.2 K, compo unds with R = OC12H25 and R = F show substantial coercivity and remanant ma gnetization. For the first sample, the magnetization jump at the virgin cur ve, 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) 199 9 Elsevier Science B.V. All rights reserved.