J. Phys. I France 3 (1993) 1153-1174
Electronic magnetic resonance in a series of antiferromagnetic molecular perovskitesC. Coulon1, C. Livage2, L. Gonzalvez1, K. Boubekeur2 and P. Batail2
1 CNRS, Centre de Recherche P. Pascal, Avenue du Dr Schweitzer, 33600 Pessac, France
2 Laboratoire de Physique des Solides Associé au CNRS, Université Paris-Sud, 91405 Orsay, France
(Received 11 December 1992, accepted 27 January 1993)
The magnetic properties of a series of ternary tetrathiafulvalenium (TTF +) salts incorporating, within a unique antiperovskite structure, a discrete halide (Y = Cl -, Br - or I -) in addition to an octahedral molybdenum halide cluster dianion Mo 6X 142- (with X = Cl or Br), are described. The preparation and structural chemistry of the materials of general formula (TTF +) 3 (Mo 6X 142-)(Y -) are briefly recalled. The single-crystal electronic magnetic resonance is explored in details using an X-band ESR spectrometer, both in the paramagnetic state where a narrow EPR signal is observed, as well as in the low temperature antiferromagnetic phase where antiferromagnetic resonance (AFMR) is detected. A quantitative discussion of the resonance field and linewidth is given in both regimes. The EPR line characteristics are shown to be strongly sensitive to the TTF + environment, namely, the nature of the halide on both anion sites and small variations in intermolecular interactions, which reveal the importance of the spin-orbit coupling. On the other hand, AFMR data are discussed in terms of a dominant dipole-dipole interaction as found previously for other TTF-based cation radical salts. Finally, similar albeit contrasted results are obtained with the isomorphous, chalcohalide rhenium cluster dianion-based ternary salt (TTF +) 3(Re 6S 6C 2-8)(Cl -), which allow for a discussion of the AFMR lineshape.
76.30 - 75.50
© Les Editions de Physique 1993